Subject: [IPFIX] draft-ietf-ipfix-anon-02.txt: WG last call review

From: Benoit Claise <[email-masked]>
Date: Fri, 02 Apr 2010 14:42:31 +0300

Dear authors,

I review this draft.
You should consider the comments in sequence.

Regards, Benoit.
> IPFIX Working Group                                            E. Boschi
> Internet-Draft                                               B. Trammell
> Intended status: Experimental                             Hitachi Europe
> Expires: August 19, 2010                               February 15, 2010
>
>                       IP Flow Anonymisation Support
>                        draft-ietf-ipfix-anon-02.txt
>
> Abstract
>
>     This document describes anonymisation techniques for IP flow data and
>     the export of anonymised data using the IPFIX protocol.  It
>     categorizes common anonymisation schemes and defines the parameters
>     needed to describe them.  It provides guidelines for the
>     implementation of anonymised data export and storage over IPFIX, and
>     describes an information model and Options-based method for
>     anonymisation technique metadata export within the IPFIX protocol or
>     storage in IPFIX Files.
>
> Status of this Memo
>
>     This Internet-Draft is submitted to IETF in full conformance with the
>     provisions of BCP 78 and BCP 79.
>
>     Internet-Drafts are working documents of the Internet Engineering
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>
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>
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>
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>
>     This Internet-Draft will expire on August 19, 2010.
>
> Copyright Notice
>
>     Copyright (c) 2010 IETF Trust and the persons identified as the
>     document authors.  All rights reserved.
>
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>     This document is subject to BCP 78 and the IETF Trust's Legal
>     Provisions Relating to IETF Documents
>     (http://trustee.ietf.org/license-info) in effect on the date of
>     publication of this document.  Please review these documents
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>     include Simplified BSD License text as described in Section 4.e of
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>     described in the BSD License.
>
> Table of Contents
>
>     1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
>       1.1.  IPFIX Protocol Overview  . . . . . . . . . . . . . . . . .  4
>       1.2.  IPFIX Documents Overview . . . . . . . . . . . . . . . . .  5
>       1.3.  Anonymisation within the IPFIX Architecture  . . . . . . .  5
>     2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  7
>     3.  Categorisation of Anonymisation Techniques . . . . . . . . . .  7
>     4.  Anonymisation of IP Flow Data  . . . . . . . . . . . . . . . .  8
>       4.1.  IP Address Anonymisation . . . . . . . . . . . . . . . . . 10
>         4.1.1.  Truncation . . . . . . . . . . . . . . . . . . . . . . 10
>         4.1.2.  Reverse Truncation . . . . . . . . . . . . . . . . . . 11
>         4.1.3.  Permutation  . . . . . . . . . . . . . . . . . . . . . 11
>         4.1.4.  Prefix-preserving Pseudonymisation . . . . . . . . . . 11
>       4.2.  Hardware Address Anonymisation . . . . . . . . . . . . . . 12
>         4.2.1.  Reverse Truncation . . . . . . . . . . . . . . . . . . 12
>         4.2.2.  Permutation  . . . . . . . . . . . . . . . . . . . . . 13
>         4.2.3.  Structured Pseudonymisation  . . . . . . . . . . . . . 13
>       4.3.  Timestamp Anonymisation  . . . . . . . . . . . . . . . . . 13
>         4.3.1.  Precision Degradation  . . . . . . . . . . . . . . . . 13
>         4.3.2.  Enumeration  . . . . . . . . . . . . . . . . . . . . . 14
>         4.3.3.  Random Shifts  . . . . . . . . . . . . . . . . . . . . 14
>       4.4.  Counter Anonymisation  . . . . . . . . . . . . . . . . . . 14
>         4.4.1.  Precision Degradation  . . . . . . . . . . . . . . . . 15
>         4.4.2.  Binning  . . . . . . . . . . . . . . . . . . . . . . . 15
>         4.4.3.  Random Noise Addition  . . . . . . . . . . . . . . . . 15
>       4.5.  Anonymisation of Other Flow Fields . . . . . . . . . . . . 16
>         4.5.1.  Binning  . . . . . . . . . . . . . . . . . . . . . . . 16
>         4.5.2.  Permutation  . . . . . . . . . . . . . . . . . . . . . 16
>     5.  Parameters for the Description of Anonymisation Techniques . . 16
>       5.1.  Stability  . . . . . . . . . . . . . . . . . . . . . . . . 17
>       5.2.  Truncation Length  . . . . . . . . . . . . . . . . . . . . 17
>    
>       5.3.  Bin Map  . . . . . . . . . . . . . . . . . . . . . . . . . 17
>       5.4.  Permutation  . . . . . . . . . . . . . . . . . . . . . . . 18
>       5.5.  Shift Amount . . . . . . . . . . . . . . . . . . . . . . . 18
>     6.  Anonymisation Export Support in IPFIX  . . . . . . . . . . . . 18
>       6.1.  Anonymisation Options Template . . . . . . . . . . . . . . 18
>
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>       6.2.  Recommended Information Elements for Anonymisation
>             Metadata . . . . . . . . . . . . . . . . . . . . . . . . . 20
>         6.2.1.  informationElementIndex  . . . . . . . . . . . . . . . 20
>         6.2.2.  anonymisationFlags . . . . . . . . . . . . . . . . . . 20
>         6.2.3.  anonymisationTechnique . . . . . . . . . . . . . . . . 22
>     7.  Applying Anonymisation Techniques to IPFIX Export and
>         Storage  . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
>       7.1.  Arrangement of Processes in IPFIX Anonymisation  . . . . . 24
>       7.2.  IPFIX-Specific Anonymisation Guidelines  . . . . . . . . . 27
>         7.2.1.  Appropriate Use of Information Elements for
>                 Anonymised Data  . . . . . . . . . . . . . . . . . . . 27
>         7.2.2.  Export of Perimeter-Based Anonymisation Policies . . . 28
>         7.2.3.  Anonymisation of Header Data . . . . . . . . . . . . . 28
>         7.2.4.  Anonymisation of Options Data  . . . . . . . . . . . . 29
>         7.2.5.  Special-Use Address Space Considerations . . . . . . . 30
>     8.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
>     9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 33
>     10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 34
>     11. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 35
>     12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 35
>       12.1. Normative References . . . . . . . . . . . . . . . . . . . 35
>       12.2. Informative References . . . . . . . . . . . . . . . . . . 35
>     Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 36
>
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> 1.  Introduction
>
>     The standardisation of an IP flow information export protocol
>     [RFC5101] and associated representations removes a technical barrier
>     to the sharing of IP flow data across organizational boundaries and
>     with network operations, security, and research communities for a
>     wide variety of purposes.  However, with wider dissemination comes
>     greater risks to the privacy of the users of networks under
>     measurement, and to the security of those networks.  While it is not
>     a complete solution to the issues posed by distribution of IP flow
>     information, anonymisation (i.e., the deletion or transformation of
>     information that is considered sensitive and could be used to reveal
>     the identity of subjects involved in a communication) is an important
>     tool for the protection of privacy within network measurement
>     infrastructures.
>
>     This document presents a mechanism for representing anonymised data
>     within IPFIX and guidelines for using it.  It begins with a
>     categorization of anonymisation techniques.  It then describes
>     applicability of each technique to commonly anonymisable fields of IP
>     flow data, organized by information element data type and semantics
>     as in [RFC5102]; enumerates the parameters required by each of the
>     applicable anonymisation techniques; and provides guidelines for the
>     use of each of these techniques in accordance with best practices in
>     data protection.  Finally, it specifies a mechanism for exporting
>     anonymised data and binding anonymisation metadata to templates using
>     IPFIX Options.
>
> 1.1.  IPFIX Protocol Overview
>
>     In the IPFIX protocol, { type, length, value } tuples are expressed
>     in templates containing { type, length } pairs, specifying which {
>     value } fields are present in data records conforming to the
>     Template, giving great flexibility as to what data is transmitted.
>     Since Templates are sent very infrequently compared with Data
>     Records, this results in significant bandwidth savings.  Various
>     different data formats may be transmitted simply by sending new
>     Templates specifying the { type, length } pairs for the new data
>     format.  See [RFC5101] for more information.
>
>     The IPFIX information model [RFC5102] defines a large number of
>     standard Information Elements which provide the necessary { type }
>     information for Templates.  The use of standard elements enables
>     interoperability among different vendors' implementations.
>     Additionally, non-standard enterprise-specific elements may be
>     defined for private use.
>
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> 1.2.  IPFIX Documents Overview
>
>     "Specification of the IPFIX Protocol for the Exchange of IP Traffic
>     Flow Information" [RFC5101] and its associated documents define the
>     IPFIX Protocol, which provides network engineers and administrators
>     with access to IP traffic flow information.
>
>     "Architecture for IP Flow Information Export" [RFC5470] defines the
>     architecture for the export of measured IP flow information out of an
>     IPFIX Exporting Process to an IPFIX Collecting Process, and the basic
>     terminology used to describe the elements of this architecture, per
>     the requirements defined in "Requirements for IP Flow Information
>     Export" [RFC3917].  The IPFIX Protocol document [RFC5101] then covers
>     the details of the method for transporting IPFIX Data Records and
>     Templates via a congestion-aware transport protocol from an IPFIX
>     Exporting Process to an IPFIX Collecting Process.
>
>     "Information Model for IP Flow Information Export" [RFC5102]
>     describes the Information Elements used by IPFIX, including details
>     on Information Element naming, numbering, and data type encoding.
>     Finally, "IPFIX Applicability" [RFC5472] describes the various
>     applications of the IPFIX protocol and their use of information
>     exported via IPFIX, and relates the IPFIX architecture to other
>     measurement architectures and frameworks.
>
>     Additionally, "Specification of the IPFIX File Format" [RFC5655]
>     describes a file format based upon the IPFIX Protocol for the storage
>     of flow data.
>
>     This document references the Protocol and Architecture documents for
>     terminology, and extends the IPFIX Information Model to provide new
>     Information Elements for anonymisation metadata.  The anonymisation
>     techniques described herein are equally applicable to the IPFIX
>     Protocol and data stored in IPFIX Files.
>
> 1.3.  Anonymisation within the IPFIX Architecture
>
>     "Architecture for IP Flow Information Export" [RFC5470] defines the
>     functions performed in sequence by the various functional blocks in
>     an IPFIX Device as in the figure below.
>
>                      Packet(s) coming into Observation Point(s)
>                        |                                   |
>                        v                                   v
>       +----------------+-------------------------+   +-----+-------+
>       |          Metering Process on an          |   |             |
>       |             Observation Point            |   |             |
>
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>       |                                          |   |             |
>       |   packet header capturing                |   |             |
>       |        |                                 |...| Metering    |
>       |   timestamping                           |   | Process N   |
>       |        |                                 |   |             |
>       | +----->+                                 |   |             |
>       | |      |                                 |   |             |
>       | |   sampling Si (1:1 in case of no       |   |             |
>       | |      |          sampling)              |   |             |
>       | |   filtering Fi (select all when        |   |             |
>       | |      |          no criteria)           |   |             |
>       | +------+                                 |   |             |
>       |        |                                 |   |             |
>       |        |        Timing out Flows         |   |             |
>       |        |    Handle resource overloads    |   |             |
>       +--------|---------------------------------+   +-----|-------+
>                |                                           |
>        Flow Records (identified by Observation Domain)  Flow Records
>                |                                           |
>                +---------+---------------------------------+
>                          |
>     +--------------------|----------------------------------------------+
>     |                    |     Exporting Process                        |
>     |+-------------------|-------------------------------------------+  |
>     ||                   v       IPFIX Protocol                      |  |
>     ||+-----------------------------+  +----------------------------+|  |
>     |||Rules for                    |  |Functions                   ||  |
>     ||| Picking/sending Templates   |  |-Packetise selected Control ||  |
>     ||| Picking/sending Flow Records|->|&  data Information into   ||  |
>     ||| Encoding Template&  data    |  |  IPFIX export packets.     ||  |
>     ||| Selecting Flows to export(*)|  |-Handle export errors       ||  |
>     ||+-----------------------------+  +----------------------------+|  |
>     |+----------------------------+----------------------------------+  |
>     |                             |                                     |
>     |                    exported IPFIX Messages                        |
>     |                             |                                     |
>     |                +------------+-----------------+                   |
>     |                |  Anonymise export packet(*)  |                   |
>     |                +------------+-----------------+                   |
>     |                             |                                     |
>     |                +------------+-----------------+                   |
>     |                |       Transport  Protocol    |                   |
>     |                +------------+-----------------+                   |
>     |                             |                                     |
>     +-----------------------------+-------------------------------------+
>                                   |
>                                   v
>                      IPFIX export packet to Collector
>
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>     (*) indicates that the block is optional.
>    
In the general architecture, but not in this spec. right?
>                   Figure 1: IPFIX Device functional blocks
>    
I was hoping to get the reference model from the IPFIX Mediator framework.
If the reference model was from the IPFIX Mediator framework, then we 
would not have the issue with optional.
>     Note that, according to the original architecture specification,
>    
What is this? RFC5470?
>     IPFIX Message anonymisation is optionally performed as the final
>     operation before handing the Message to the transport protocol for
>     export.  While no provision is made in the architecture for
>     anonymisation metadata as in Section 6, this arrangement does allow
>     for the message rewriting necessary for comprehensive anonymisation
>     of IPFIX export as in Section 7.  The development of the IPFIX
>     Mediation [I-D.ietf-ipfix-mediators-framework] framework and the
>     IPFIX File Format [RFC5655] expand upon this initial architectural
>     allowance for anonymisation by adding to the list of places that
>     anonymisation may be applied.  The former specifies IPFIX Mediators,
>     which rewrite existing IPFIX messages, and the latter specifies a
>    
IPFIX Message?
It would be nice to say in the terminology section which terms you use 
from other RFCs.
For example, data set vs dataset versus Data Set
For example, flow records is lower case, but I see IPFIX File, Options 
Template
Please be consistent with capitalization

>     method for storage of IPFIX data in files.
>
>     More detail on the applicable architectural arrangements of
>     anonymisation can be found in Section 7.1
>
> 2.  Terminology
>
>     Terms used in this document that are defined in the Terminology
>     section of the IPFIX Protocol [RFC5101] document are to be
>     interpreted as defined there.
>
>     The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
>     "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
>     document are to be interpreted as described in RFC 2119 [RFC2119].
>
> 3.  Categorisation of Anonymisation Techniques
>
>     Anonymisation modifies a data set in order to protect the identity of
>     the people or entities described by the data set from disclosure.
>     With respect to network traffic data, anonymisation generally
>     attempts to preserve some set of properties of the network traffic
>     useful for a given application or applications, while ensuring the
>     data cannot be traced back to the specific networks, hosts, or users
>     generating the traffic.
>
>     Anonymisation may be broadly classified according to two properties:
>     recoverability and countability.  All anonymisation techniques map
>     the real space of identifiers or values into a separate, anonymised
>     space, according to some function.  A technique is said to be
>
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>     recoverable when the function used is invertible or can otherwise be
>     reversed and a real identifier can be recovered from a given
>     replacement identifier.
>
>     Countability compares the dimension of the anonymised space (N) to
>     the dimension of the real space (M), and denotes how the count of
>     unique values is preserved by the anonymisation function.  If the
>     anonymised space is smaller than the real space, then the function is
>     said to generalise the input, mapping more than one input point to
>     each anonymous value (e.g., as with aggregation).  By definition,
>     generalisation is not recoverable.
>
>     If the dimensions of the anonymised and real spaces are the same,
>     such that the count of unique values is preserved, then the function
>     is said to be a direct substitution function.  If the dimension of
>     the anonymised space is larger, such that each real value maps to a
>     set of anonymised values, then the function is said to be a set
>     substitution function.  Note that with set substitution functions,
>     the sets of anonymised values are not necessarily disjoint.  Either
>     direct or set substitution functions are said to be one-way if there
>     exists no practical method for recovering the real data point from an
>     anonymised one.
>
>     This classification is summarised in the table below.
>
>     +------------------------+-----------------+------------------------+
>     | Recoverability /       | Recoverable     | Non-recoverable        |
>     | Countability           |                 |                        |
>     +------------------------+-----------------+------------------------+
>     | N<  M                  | N.A.            | Generalisation         |
>     | N = M                  | Direct          | One-way Direct         |
>     |                        | Substitution    | Substitution           |
>     | N>  M                  | Set             | One-way Set            |
>     |                        | Substitution    | Substitution           |
>     +------------------------+-----------------+------------------------+
>
> 4.  Anonymisation of IP Flow Data
>
>     Due to the restricted semantics of IP flow data, there is a
>     relatively limited set of specific anonymisation techniques available
>     on flow data, though each falls into the broad categories above.
>     Each type of field that may commonly appear in a flow record may have
>     its own applicable specific techniques.
>
>     While anonymisation is generally applied at the resolution of single
>     fields within a flow record, attacks against anonymisation use entire
>     flows and relationships between hosts and flows within a given data
>
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>     set.  Therefore, fields which may not necessarily be identifying by
>     themselves may be anonymised in order to increase the anonymity of
>     the data set as a whole.
>
>     Of all the fields in an IP flow record, IP addresses are the most
>     likely to be used to directly identify entities in the real world.
>     Each IP address is associated with an interface on a network host,
>     and can potentially be identified with a single user.  Additionally,
>     IP addresses are structured identifiers; that is, partial IP address
>     prefixes may be used to identify networks just as full IP addresses
>     identify hosts.  This makes anonymisation of IP addresses
>     particularly important.
>
>     Hardware addresses uniquely identify devices on the network; while
>     they are not often available in traffic data collected at Layer 3,
>     and cannot be used to locate devices within the network, some traces
>     may contain sub-IP data including hardware address data.  Hardware
>     addresses may be mappable to device serial numbers, and to the
>     entities or individuals who purchased the devices, when combined with
>     external databases.  They may also leak via IPv6 addresses in certain
>     circumstances.  Therefore, hardware address anonymisation is also
>     important.
>    
I would clearly mention MAC address
>     Port numbers identify abstract entities (applications) as opposed to
>     real-world entities, but they can be used to classify hosts and user
>     behavior.  Passive port fingerprinting, both of well-known and
>     ephemeral ports, can be used to determine the operating system
>     running on a host.  Relative data volumes by port can also be used to
>     determine the host's function (workstation, web server, etc.); this
>     information can be used to identify hosts and users.
>
>     While not identifiers in and of themselves, timestamps and counters
>     can reveal the behavior of the hosts and users on a network.  Any
>     given network activity is recognizable by a pattern of relative time
>     differences and data volumes in the associated sequence of flows,
>     even without host address information.  They can therefore be used to
>     identify hosts and users.  Timestamps and counters are also
>     vulnerable to traffic injection attacks, where traffic with a known
>     pattern is injected into a network under measurement, and this
>     pattern is later identified in the anonymised data set.
>
>     The simplest and most extreme form of anonymisation, which can be
>     applied to any field of a flow record, is black-marker anonymisation,
>     or complete deletion of a given field.  Note that black-marker
>     anonymisation is equivalent to simply not exporting the field(s) in
>     question.
>
>     While black-marker anonymisation completely protects the data in the
>
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>     deleted fields from the risk of disclosure, it also reduces the
>     utility of the anonymised data set as a whole.  Techniques that
>     retain some information while reducing (though not eliminating) the
>     disclosure risk will be extensively discussed in the following
>     sections; note that the techniques specifically applicable to IP
>     addresses, timestamps, ports, and counters will be discussed in
>     separate sections.
>
> 4.1.  IP Address Anonymisation
>
>     Since IP addresses are the most common identifiers within flow data
>     that can be used to directly identify a person, organization, or
>     host, most of the work on flow and trace data anonymisation has gone
>     into IP address anonymisation techniques.  Indeed, the aim of most
>     attacks against anonymisation is to recover the map from anonymised
>     IP addresses to original IP addresses thereby identifying the
>     identified hosts.  There is therefore a wide range of IP address
>     anonymisation schemes that fit into the following categories.
>
>         +------------------------------------+---------------------+
>         | Scheme                             | Action              |
>         +------------------------------------+---------------------+
>         | Truncation                         | Generalisation      |
>         | Reverse Truncation                 | Generalisation      |
>         | Permutation                        | Direct Substitution |
>         | Prefix-preserving Pseudonymisation | Direct Substitution |
>         +------------------------------------+---------------------+
>
> 4.1.1.  Truncation
>
>     Truncation removes "n" of the least significant bits from an IP
>     address, replacing them with zeroes.  In effect, it replaces a host
>     address with a network address for some fixed netblock; for IPv4
>     addresses, 8-bit truncation corresponds to replacement with a /24
>     network address.  Truncation is a non-reversible generalisation
>     scheme.  Note that while truncation is effective for making hosts
>     non-identifiable, it preserves information which can be used to
>     identify an organization, a geographic region, a country, or a
>     continent (or RIR region of responsibility).
>    
what is RIR?
>     Truncation to an address length of 0 is equivalent to black-marker
>     anonymisation.  Complete removal of IP address information is only
>     recommended for analysis tasks which have no need to separate flow
>     data by host or network; e.g. as a first stage to per-application
>     (port) or time-series total volume analyses.
>
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> 4.1.2.  Reverse Truncation
>
>     Reverse truncation removes "n" of the most significant bits from an
>     IP address, replacing them with zeroes.  Reverse truncation is a non-
>     reversible generalisation scheme.  Reverse truncation is effective
>     for making networks unidentifiable, partially or completely removing
>     information which can be used to identify an organization, a
>     geographic region, a country, or a continent (or RIR region of
>     responsibility).  However, it may cause ambiguity when applied to
>     data collected from more than one network, since it treats all the
>     hosts with the same address on different networks as if they are the
>     same host.  It is not particularly useful when publishing data where
>     the network of origin is known or can be easily guessed by virtue of
>     the identity of the publisher.
>
>     Like truncation, reverse truncation to an address length of 0 is
>     equivalent to black-marker anonymisation.
>
> 4.1.3.  Permutation
>
>     Permutation is a direct substitution technique, replacing each IP
>     address with an address selected from the set of possible IP
>     addresses, guaranteeing that each anonymised address represents a
>     unique original address.  The selection function is often random,
>     though it is not necessarily so.  Permutation does not preserve any
>     structural information about a network, but it does preserve the
>     unique count of IP addresses.  Any application that requires more
>     structure than host-uniqueness will not be able to use permuted IP
>     addresses.
>
> 4.1.4.  Prefix-preserving Pseudonymisation
>
>     Prefix-preserving pseudonymisation is a direct substitution
>     technique, like permutation but further restricted such that the
>     structure of subnets is preserved at each level while anonymising IP
>     addresses.  If two real IP addresses match on a prefix of "n" bits,
>     the two anonymised IP addresses will match on a prefix of "n" bits as
>     well.  This is useful when relationships among networks must be
>     preserved for a given analysis task, but introduces structure into
>     the anonymised data which can be exploited in attacks against the
>     anonymisation technique.
>
>     Scanning in Internet background traffic can cause particular problems
>     with this technique: if a scanner uses a predictable and known
>     sequence of addresses, this information can be used to reverse the
>     substitution.  The low order portion of the address can be left
>     unanonymized as a partial defense against this attack.
>
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>
> 4.2.  Hardware Address Anonymisation
>
>     Flow data containing sub-IP information can also contain identifying
>     information in the form of the hardware (MAC) address.  While
>     hardware address information cannot be used to locate a node within a
>     network, it can be used to directly uniquely identify a specific
>     device.  Vendors or organizations within the supply chain may then
>     have the information necessary to identify the entity or individual
>     that purchased the device.
>
>     Hardware address information is not as structured as IP address
>     information.  EUI-48 and EUI-64 hardware addresses contain an
>     Organizational Unique Identifier in the three most significant bytes
>     of the address; this OUI additionally contains bits noting whether
>     the address is locally or globally administered.  Beyond this, the
>     address is unstructured, and there is no particular relationship
>     among the OUIs assigned to a given vendor.
>
>     Note that hardware address information also appear within IPv6
>     addresses, as the EAP-64 address, or EAP-48 address encoded as an
>     EAP-64 address, is used as the least significant 64 bits of the IPv6
>     address in the case of link local addressing or stateless
>     autoconfiguration; the considerations and techniques in this section
>     may then apply to such IPv6 addresses as well.
>
>             +-----------------------------+---------------------+
>             | Scheme                      | Action              |
>             +-----------------------------+---------------------+
>             | Reverse Truncation          | Generalisation      |
>             | Permutation                 | Direct Substitution |
>             | Structured Pseudonymisation | Direct Substitution |
>             +-----------------------------+---------------------+
>
> 4.2.1.  Reverse Truncation
>
>     Reverse truncation removes "n" of the most significant bits from an
>     MAC address, replacing them with zeroes.  Reverse truncation is a
>     non-reversible generalisation scheme.  This has the effect of
>     removing bits of the OUI, which identify manufacturers, before
>     removing the least significant bits.  Reverse truncation of 24 bits
>     zeroes out the OUI.
>
>     Reverse truncation is effective for making device manufacturers
>     partially or completely unidentifiable within a dataset.  However, it
>     may cause ambiguity by introducing the possibility of truncated MAC
>     address collision.  Also note that the utility or removing
>     manufacturer information is dubious, and not particularly well-
>     covered by the literature.
>
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>
>     Reverse truncation to an address length of 0 is equivalent to black-
>     marker anonymisation.
>
> 4.2.2.  Permutation
>
>     Permutation is a direct substitution technique, replacing each MAC
>     address with an address selected from the set of possible MAC
>     addresses, guaranteeing that each anonymised address represents a
>     unique original address.  The selection function is often random,
>     though it is not necessarily so.  Permutation does not preserve any
>     structural information about a network, but it does preserve the
>     unique count of devices on the network.  Any application that
>     requires more structure than host-uniqueness will not be able to use
>     permuted MAC addresses.
>
> 4.2.3.  Structured Pseudonymisation
>
>     Structured pseudonymisation for MAC addresses is a direct
>     substitution technique, like permutation, but restricted such that
>     the OUI (the most significant three bytes) is permuted separately
>     from the node identifier, the remainder.  This is useful when the
>     uniqueness of OUIs must be preserved for a given analysis task, but
>     introduces structure into the anonymised data which can be exploited
>     in attacks against the anonymisation technique.
>
> 4.3.  Timestamp Anonymisation
>
>     The particular time at which a flow began or ended is not
>     particularly identifiable information, but it can be used as part of
>     attacks against other anonymisation techniques or for user profiling.
>     Presice timestamps can be used in injected-traffic fingerprinting
>    
precise

Yo might want to describe what fingerprinting is
>     attacks as well as to identify certain activity by response delay and
>     size fingerprinting.  Therefore, timestamp information may be
>     anonymised in order to ensure the protection of the entire dataset.
>
>            +-----------------------+----------------------------+
>            | Scheme                | Action                     |
>            +-----------------------+----------------------------+
>            | Precision Degradation | Generalisation             |
>            | Enumeration           | Direct or Set Substitution |
>            | Random Shifts         | Direct Substitution        |
>            +-----------------------+----------------------------+
>
> 4.3.1.  Precision Degradation
>    
it's like truncation, but specific to time and counter, right?
>     Precision Degradation is a generalisation technique that removes the
>     most precise components of a timestamp, accounting all events
>     occurring in each given interval (e.g. one millisecond for
>
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>
>     millisecond level degradation) as simultaneous.  This has the effect
>     of potentially collapsing many timestamps into one.  With this
>     technique time precision is reduced, and sequencing may be lost, but
>     the information at which time the event occurred is preserved.  The
>     anonymised data may not be generally useful for applications which
>     require strict sequencing of flows.
>
>     Note that flow meters with low time precision (e.g. second precision,
>     or millisecond precision on high-capacity networks) perform the
>     equivalent of precision degradation anonymisation by their design.
>
>     Note also that degradation to a very low precision (e.g. on the order
>     of minutes, hours, or days) is commonly used in analyses operating on
>     time-series aggregated data, and may also be described as binning;
>     though the time scales are longer and applicability more restricted,
>     this is in principle the same operation.
>
>     Precision degradation to infinitely low precision is equivalent to
>     black-marker anonymisation.  Removal of timestamp information is only
>     recommended for analysis tasks which have no need to separate flows
>     in time, for example for counting total volumes or unique occurrences
>     of other flow keys in an entire dataset.
>
> 4.3.2.  Enumeration
>
>     Enumeration is a substitution function that retains the chronological
>     order in which events occurred while eliminating time information.
>     Timestamps are substituted by equidistant timestamps (or numbers)
>     starting from a randomly chosen start value.  The resulting data is
>     useful for applications requiring strict sequencing, but not for
>     those requiring good timing information (e.g. delay- or jitter-
>     measurement for QoS applications or SLA validation).
>
> 4.3.3.  Random Shifts
>
>     Random time shifts add a random offset to every timestamp within a
>     dataset.  This reversible substitution technique therefore retains
>     duration and inter-event interval information as well as
>     chronological order of flows.  It is primarily intended to defeat
>     traffic injection fingerprinting attacks.
>
> 4.4.  Counter Anonymisation
>
>     Counters (such as packet and octet volumes per flow) are subject to
>     fingerprinting and injection attacks against anonymisation, or for
>     user profiling as timestamps are.  Counter anonymisation can help
>     defeat these attacks, but are only usable for analysis tasks for
>     which relative or imprecise magnitudes of activity are useful.
>
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>
>     Counter information can also be completely removed, but this is only
>     recommended for analysis tasks which have no need to evaluate the
>     removed counter, for example for counting only unique occurrences of
>     other flow keys.
>
>            +-----------------------+----------------------------+
>            | Scheme                | Action                     |
>            +-----------------------+----------------------------+
>            | Precision Degradation | Generalisation             |
>            | Binning               | Generalisation             |
>            | Random noise addition | Direct or Set Substitution |
>            +-----------------------+----------------------------+
>
> 4.4.1.  Precision Degradation
>
>     As with precision degradation in timestamps, precision degradation of
>     counters removes lower-order bits of the counters, treating all the
>     counters in a given range as having the same value.  Depending on the
>     precision reduction, this loses information about the relationships
>     between sizes of similarly-sized flows, but keeps relative magnitude
>     information.  Precision degradation to an infinitely low precision is
>     equivalent to black-marker anonymisation.
>
> 4.4.2.  Binning
>
>     Binning can be seen as a special case of precision degradation; the
>     operation is identical, except for in precision degradation the
>     counter ranges are uniform, and in binning they need not be.  For
>     example, a common counter binning scheme for packet counters could be
>     to bin values 1-2 together, and 3-infinity together, thereby
>     separating potentially completely-opened TCP connections from
>     unopened ones.  Binning schemes are generally chosen to keep
>     precisely the amount of information required in a counter for a given
>     analysis task.  Note that, also unlike precision degradation, the bin
>     label need not be within the bin's range.  Binning counters to a
>     single bin is equivalent to black-marker anonymisation.
>
> 4.4.3.  Random Noise Addition
>
>     Random noise addition adds a random amount to a counter in each flow;
>     this is used to keep relative magnitude information and minimize the
>     disruption to size relationship information while avoiding
>     fingerprinting attacks against anonymisation.  Note that there is no
>     guarantee that random noise addition will maintain ranking order by a
>     counter among members of a set.  Random noise addition is
>     particularly useful when the derived analysis data will not be
>     presented in such a way as to require the lower-order bits of the
>     counters.
>
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>
> 4.5.  Anonymisation of Other Flow Fields
>
>     Other fields, particularly port numbers and protocol numbers, can be
>     used to partially identify the applications that generated the
>     traffic in a a given flow trace.  This information can be used in
>     fingerprinting attacks, and may be of interest on its own (e.g., to
>     reveal that a certain application with suspected vulnerabilities is
>     running on a given network).  These fields are generally anonymised
>     using one of two techniques.
>
>                     +-------------+---------------------+
>                     | Scheme      | Action              |
>                     +-------------+---------------------+
>                     | Binning     | Generalisation      |
>                     | Permutation | Direct Substitution |
>                     +-------------+---------------------+
>
> 4.5.1.  Binning
>
>     Binning is a generalisation technique mapping a set of potentially
>     non-uniform ranges into a set of arbitrarily labeled bins.  Common
>     bin arrangements depend on the field type and the analysis
>     application.  For example, an IP protocol bin arrangement may
>     preserve 1, 6, and 17 for ICMP, UDP, and TCP traffic, and bin all
>     other protocols into a single bin, to mitigate the use of uncommon
>     protocols in fingerprinting attacks.  Another example arrangement may
>     bin source and destination ports into low (0-1023) and high (1024-
>     65535) bins in order to tell service from ephemeral ports without
>     identifying individual applications.
>
>     Binning other flow key fields to a single bin is equivalent to black-
>     marker anonymisation.  Removal of other flow key information is only
>     recommended for analysis tasks which have no need to differentiate
>     flows on the removed keys, for example for total traffic counts or
>     unique counts of other flow keys.
>
> 4.5.2.  Permutation
>
>     Permutation is a direct substitution technique, replacing each value
>     with an value selected from the set of possible range, guaranteeing
>     that each anonymised value represents a unique original value.  This
>     is used to preserve the count of unique values without preserving
>     information about, or the ordering of, the values themselves.
>
> 5.  Parameters for the Description of Anonymisation Techniques
>
>     This section details the abstract parameters used to describe the
>
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>
>     anonymisation techniques examined in the previous section, on a per-
>     parameter basis.  These parameters and their export safety inform the
>     design of the IPFIX anonymisation metadata export specified in the
>     following section.
>    
you use different terms for metadata

    IPFIX anonymisation metadata export
    anonymisation technique metadata export
    anonymisation metadata
    metadata about exported flows and the flow collection infrastructure
    ...

You might want to be consistent

> 5.1.  Stability
>
>     Any given anonymisation technique may be applied with a varying range
>     of stability.  Stability is important for assessing the comparability
>     of anonymised information in different data sets, or in the same data
>     set over different time periods.  In general, stability ranges from
>     completely stable to completely unstable; however, note that the
>     completely unstable case is indistinguishable from black-marker
>     anonymisation.  A completely stable anonymisation will always map a
>     given value in the real space to the same value in the anonymised
>     space.  In practice, an anonymisation may also be stable for every
>     data set published by an a particular producer to a particular
>     consumer, stable for a stated time period within a dataset or across
>     datasets, or stable only for a single data set.
>
>     If no information about stability is available, users of anonymised
>     data may assume that the techniques used are stable across the entire
>     dataset, but unstable across datasets.  Note that stability presents
>     a risk-utility tradeoff, as completely stable anonymisation can be
>     used for longer-term trend analysis tasks but also presents more risk
>     of attack given the stable mapping.
>    
In this section, you don't say if you must export the content of this 
section, while you do for all the other 5.x sections
> 5.2.  Truncation Length
>
>     Truncation and precision degradation are described by the truncation
>     length, or the amount of data still remaining in the anonymised field
>     after anonymisation.
>
>     Truncation length can be inferred from a given data set, and need not
>     be specially exported or protected.
>
> 5.3.  Bin Map
>
>     Binning is described by the specification of a bin mapping function.
>     This function can be generally expressed in terms of an associative
>     array that maps each point in the original space to a bin, although
>     from an implementation standpoint most bin functions are much simpler
>     and more efficient.
>
>     Since knowledge of the bin mapping function can be used to partially
>     deanonymise binned data, depending on the degree of generalisation,
>     no information about the bin mapping function should be exported.
>
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>
> 5.4.  Permutation
>
>     Like binning, permutation is described by the specification of a
>     permutation function.  In the general case, this can be expressed in
>     terms of an associative array that maps each point in the original
>     space to a point in the anonymised space.  Unlike binning, each point
>     in the anonymised space must correspond to a single, unique point in
>     the original space.
>
>     Since knowledge of the permutation function can be used to completely
>     deanonymise permuted data, no information about the permutation
>     function or its parameters should be exported.
>
> 5.5.  Shift Amount
>
>     Shifting requires an amount to shift each value by.  Since the shift
>     amount can be used to deanonymise data protected by shifting, no
>     information about the shift amount should be exported.
>
> 6.  Anonymisation Export Support in IPFIX
>
>     Anonymised data exported via IPFIX SHOULD be annotated with
>     anonymisation metadata, which details which fields described by which
>     Templates are anonymised, and provides appropriate information on the
>     anonymisation techniques used.  This metadata SHOULD be exported in
>     Data Records described by the recommended Options Templates described
>     in this section; these Options Templates use the additional
>     Information Elements described in the following subsection.
>
>     Note that fields anonymised using the black-marker (removal)
>     technique do not require any special metadata support.  Black-marker
>     anonymised fields SHOULD NOT be exported at all; the absence of the
>    
MUST NOT?
>     field in a given Data Set is implicitly declared by not including the
>     corresponding Information Element in the Template describing that
>     Data Set.
>
> 6.1.  Anonymisation Options Template
>
>     The Anonymisation Options Template describes anonymisation records,
>     which allow anonymisation metadata to be exported inline over IPFIX
>     or stored in an IPFIX File, by binding information about
>     anonymisation techniques to Information Elements within defined
>     Templates.  IPFIX Exporting Processes SHOULD export anonymisation
>     records for any Template describing exported anonymised Data Records;
>    
an anonymization record is actually a data record of the Anonymization 
Options Template Record, as opposed to an anonymized record.
It would be better to define those terms, no

>     IPFIX Collecting Processes and processes downstream from them MAY use
>     anonymisation records to treat anonymised data differently depending
>     on the applied technique.
>
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>
>     An Exporting Process SHOULD export anonymisation records after the
>     Templates they describe have been exported,
And MUST send the anonymization record before the anomized records?

Do you want to benefit from the per-stream SCTP draft.
That would solve most of your problems: order, reliable
Otherwise, if the collector doesn't have received the anonimization 
records, then it might be treating the flow records wrongly.
>   and SHOULD export
>     anonymisation records reliably.
>
>     Anonymisation records, like Templates, MUST be handled by Collecting
>     Processes as scoped to the Transport Session in which they are sent.
>     While the Stability Class within the anonymisationFlags IE can be
>     used to declare that a given anonymisation technique's mapping will
>     remain stable across multiple sessions, each session MUST re-export
>     the anonymisation Records along with the templates.
>
>     +-------------------------+-----------------------------------------+
>     | IE                      | Description                             |
>     +-------------------------+-----------------------------------------+
>     | templateId [scope]      | The Template ID of the Template         |
>     |                         | containing the Information Element      |
>     |                         | described by this anonymisation record. |
>     |                         | This Information Element MUST be        |
>     |                         | defined as a Scope Field.               |
>     | informationElementId    | The Information Element identifier of   |
>     | [scope]                 | the Information Element described by    |
>     |                         | this anonymisation record.  This        |
>     |                         | Information Element MUST be defined as  |
>     |                         | a Scope Field.                          |
>     | informationElementId    | The Private Enterprise Number of the    |
>     | [scope] [optional]      | enterprise-specific Information Element |
>     |                         | described by this anonymisation record. |
>     |                         | This Information Element MUST be        |
>     |                         | defined as a Scope Field if present.    |
>    
Isn't it privateEnterpriseNumber instead of informationElementId?
Actually, the example and the description mention privateEnterpriseNumber
However, I'm wondering why you need this privateEnterpriseNumber at 
all,  because the "E" bit is already part of informationElementId

  0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |E|  Information Element ident. |        Field Length           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                      Enterprise Number                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

I'm confused.

>     | informationElementIndex | The Information Element index of the    |
>     | [scope] [optional]      | instance of the Information Element     |
>     |                         | described by this anonymisation record  |
>     |                         | identified by the informationElementId  |
>     |                         | within the Template.  Optional; need    |
>     |                         | only be present when describing         |
>     |                         | Templates that have multiple instances  |
>     |                         | of the same Information Element.  This  |
>     |                         | Information Element MUST be defined as  |
>     |                         | a Scope Field if present.  This         |
>     |                         | Information Element is defined in       |
>     |                         | Section 6.2, below.                     |
>     | anonymisationFlags      | Flags describing the mapping stability  |
>     |                         | and specialized modifications to the    |
>     |                         | Anonymisation Technique in use.  SHOULD |
>     |                         | be present.  This Information Element   |
>     |                         | is defined in Section 6.2, below.       |
>
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>
>     | anonymisationTechnique  | The technique used to anonymise the     |
>     |                         | data.  MUST be present.  This           |
>     |                         | Information Element is defined in       |
>     |                         | Section 6.2, below.                     |
>     +-------------------------+-----------------------------------------+
>
> 6.2.  Recommended Information Elements for Anonymisation Metadata
>
> 6.2.1.  informationElementIndex
>
>     Description:   A zero-based index of an Information Element
>        referenced by informationElementId within a Template referenced by
>        templateId; used to disambiguate scope for templates containing
>        multiple identical Information Elements.
>
>     Abstract Data Type:   unsigned16
>
>     ElementId:   TBD3
>
>     Status:   Proposed
>
> 6.2.2.  anonymisationFlags
>
>     Description:   A flag word describing specialized modifications to
>        the anonymisation policy in effect for the anonymisation technique
>        applied to a referenced Information Element within a referenced
>        Template.  When flags are clear (0), the normal policy (as
>        described by anonymisationTechnique) applies without modification.
>
>        MSB   14  13  12  11  10   9   8   7   6   5   4   3   2   1  LSB
>        +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
>        |                Reserved                       |LOR|PmA|   SC  |
>        +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
>
>                              anonymisationFlags IE
>
>     +--------+----------+-----------------------------------------------+
>     | bit(s) | name     | description                                   |
>     | (LSB = |          |                                               |
>     | 0)     |          |                                               |
>     +--------+----------+-----------------------------------------------+
>     | 0-1    | SC       | Stability Class: see the Stability Class      |
>     |        |          | table below, and section Section 5.1.         |
>
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>
>     | 2      | PmA      | Perimeter Anonymisation: when set (1), source |
>    
source based on what? I remember the lengthy discussion in biflow.
>     |        |          | address Information Elements are interpreted  |
>     |        |          | as external addresses, and destination        |
>     |        |          | address Information Elements are interpreted  |
>     |        |          | as internal addresses, for the purposes of    |
>     |        |          | associating anonymisationTechnique to         |
>     |        |          | Information Elements.  MUST NOT be set when   |
>     |        |          | associated with a non-endpoint (i.e., source- |
>     |        |          | or destination-) Information Element.  SHOULD |
>     |        |          | be consistent within a record (i.e., if a     |
>     |        |          | source- Information Element has this flag     |
>     |        |          | set, the corresponding destination- element   |
>     |        |          | SHOULD have this flag set, and vice-versa.)   |
>     | 3      | LOR      | Low-Order Unchanged: when set (1), the        |
>     |        |          | low-order bits of the anonymised Information  |
>     |        |          | Element contain real data.  This modification |
>     |        |          | is intended for the anonymisation of          |
>     |        |          | network-level addresses while leaving         |
>     |        |          | host-level addresses intact in order to       |
>     |        |          | preserve host level-structure, which could    |
>     |        |          | otherwise be used to reverse anonymisation.   |
>     |        |          | MUST NOT be set when associated with a        |
>     |        |          | truncation-based anonymisationTechnique.      |
>     | 4-15   | Reserved | Reserved for future use: SHOULD be cleared    |
>     |        |          | (0) by the Exporting Process and MUST be      |
>     |        |          | ignored by the Collecting Process.            |
>     +--------+----------+-----------------------------------------------+
>
>        The Stability Class portion of this flags word describes the
>        stability class of the anonymisation technique applied to a
>        referenced Information Element within a referenced Template.
>        Stability classes refer to the stability of the parameters of the
>        anonymisation technique, and therefore the comparability of the
>        mapping between the real and anonymised values over time.  This
>        determines which anonymised datasets may be compared with each
>        other.  Values are as follows:
>
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>     +-----+-----+-------------------------------------------------------+
>     | Bit | Bit | Description                                           |
>     | 1   | 0   |                                                       |
>     +-----+-----+-------------------------------------------------------+
>     | 0   | 0   | Undefined: the Exporting Process makes no             |
>     |     |     | representation as to how stable the mapping is, or    |
>     |     |     | over what time period values of this field will       |
>     |     |     | remain comparable; while the Collecting Process MAY   |
>     |     |     | assume Session level stability, Session level         |
>     |     |     | stability is not guaranteed.  Processes SHOULD assume |
>     |     |     | this is the case in the absence of stability class    |
>     |     |     | information; this is the default stability class.     |
>     | 0   | 1   | Session: the Exporting Process will ensure that the   |
>     |     |     | parameters of the anonymisation technique are stable  |
>     |     |     | during the Transport Session.  All the values of the  |
>     |     |     | described Information Element for each Record         |
>     |     |     | described by the referenced Template within the       |
>     |     |     | Transport Session are comparable.  The Exporting      |
>     |     |     | Process SHOULD endeavour to ensure at least this      |
>     |     |     | stability class.                                      |
>     | 1   | 0   | Exporter-Collector Pair: the Exporting Process will   |
>     |     |     | ensure that the parameters of the anonymisation       |
>     |     |     | technique are stable across Transport Sessions over   |
>     |     |     | time with the given Collecting Process, but may use   |
>     |     |     | different parameters for different Collecting         |
>     |     |     | Processes.  Data exported to different Collecting     |
>     |     |     | Processes is not comparable.                          |
>     | 1   | 1   | Stable: the Exporting Process will ensure that the    |
>     |     |     | parameters of the anonymisation technique are stable  |
>     |     |     | across Transport Sessions over time, regardless of    |
>     |     |     | the Collecting Process to which it is sent.           |
>     +-----+-----+-------------------------------------------------------+
>
>     Abstract Data Type:   unsigned16
>
>     ElementId:   TBD1
>
>     Status:   Proposed
>
> 6.2.3.  anonymisationTechnique
>    
While reading, it looks more logical to have the anonymisationTechnique 
before the anonymizationFlags IE
>     Description:   A description of the anonymisation technique applied
>        to a referenced Information Element within a referenced Template.
>    
And options template as well? For example, in my company, we export a 
options template record with the sampling rates.
This is something I missed completely, and is valid for all IEs
>        Each technique may be applicable only to certain Information
>        Elements and recommended only for certain Infomation Elements;
>        these restrictions are noted in the table below.
>
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>     +-------+---------------------------+-----------------+-------------+
>     | Value | Description               | Applicable to   | Recommended |
>     |       |                           |                 | for         |
>     +-------+---------------------------+-----------------+-------------+
>     | 0     | Undefined: the Exporting  | all             | all         |
>     |       | Process makes no          |                 |             |
>     |       | representation as to      |                 |             |
>     |       | whether the defined field |                 |             |
>     |       | is anonymised or not.     |                 |             |
>     |       | While the Collecting      |                 |             |
>     |       | Process MAY assume that   |                 |             |
>     |       | the field is not          |                 |             |
>     |       | anonymised, it is not     |                 |             |
>     |       | guaranteed not to be.     |                 |             |
>     |       | This is the default       |                 |             |
>     |       | anonymisation technique.  |                 |             |
>     | 1     | None: the values exported | all             | all         |
>     |       | are real.                 |                 |             |
>     | 2     | Precision                 | all             | all         |
>     |       | Degradation/Truncation:   |                 |             |
>     |       | the values exported are   |                 |             |
>     |       | anonymised using simple   |                 |             |
>     |       | precision degradation or  |                 |             |
>     |       | truncation.  The new      |                 |             |
>     |       | precision or number of    |                 |             |
>     |       | truncated bits is         |                 |             |
>     |       | implicit in the exported  |                 |             |
>     |       | data, and can be deduced  |                 |             |
>     |       | by the Collecting         |                 |             |
>     |       | Process.                  |                 |             |
>     | 3     | Binning: the values       | all             | all         |
>     |       | exported are anonymised   |                 |             |
>     |       | into bins.                |                 |             |
>     | 4     | Enumeration: the values   | all             | timestamps  |
>     |       | exported are anonymised   |                 |             |
>     |       | by enumeration.           |                 |             |
>     | 5     | Permutation: the values   | all             | identifiers |
>     |       | exported are anonymised   |                 |             |
>     |       | by random permutation.    |                 |             |
>
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>     | 6     | Structured Permutation:   | addresses       |             |
>     |       | the values exported are   |                 |             |
>     |       | anonymised by random      |                 |             |
>     |       | permutation, preserving   |                 |             |
>     |       | bit-level structure as    |                 |             |
>     |       | appropriate; this         |                 |             |
>     |       | represents                |                 |             |
>     |       | prefix-preserving IP      |                 |             |
>     |       | address anonymisation or  |                 |             |
>     |       | structured MAC address    |                 |             |
>     |       | anonymisation.            |                 |             |
>     | 7     | Reverse Truncation: the   | addresses       |             |
>     |       | values exported are       |                 |             |
>     |       | anonymised using reverse  |                 |             |
>     |       | truncation.  The number   |                 |             |
>     |       | of truncated bits is      |                 |             |
>     |       | implicit in the exported  |                 |             |
>     |       | data, and can be deduced  |                 |             |
>     |       | by the Collecting         |                 |             |
>     |       | Process.                  |                 |             |
>     | 8     | Noise: the values         | non-identifiers | counters    |
>     |       | exported are anonymised   |                 |             |
>     |       | by adding random noise to |                 |             |
>     |       | each value.               |                 |             |
>     | 9     | Offset: the values        | all             | timestamps  |
>     |       | exported are anonymised   |                 |             |
>     |       | by adding a single offset |                 |             |
>     |       | to all values.            |                 |             |
>     +-------+---------------------------+-----------------+-------------+
>
>     Abstract Data Type:   unsigned16
>
>     ElementId:   TBD2
>
>     Status:   Proposed
>
> 7.  Applying Anonymisation Techniques to IPFIX Export and Storage
>
>     When exporting or storing anonymised flow data using IPFIX, certain
>     interactions between the IPFIX Protocol and the anonymisation
>     techniques in use must be considered; these are treated in the
>     subsections below.
>
> 7.1.  Arrangement of Processes in IPFIX Anonymisation
>
>     Anonymisation may be applied to IPFIX data at three stages within the
>     collection infrastructure: on initial export, at a mediator, or after
>    

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>
>     collection, as shown in Figure 2.  Each of these locations has
>     specific considerations and applicability.
>
>                 +==========================================+
>                 | Exporting Process                        |
>                 +==========================================+
>                   |                                      |
>                   |    (Anonymised at Original Exporter) |
>                   V                                      |
>                 +=============================+          |
>                 | Mediator                    |          |
>                 +=============================+          |
>                   |                                      |
>                   | (Anonymising Mediator)               |
>                   V                                      V
>                 +==========================================+
>                 | Collecting Process                       |
>                 +==========================================+
>                         |
>                         | (Anonymising CP/File Writer)
>                         V
>                 +--------------------+
>                 | IPFIX File Storage |
>                 +--------------------+
>
>                  Figure 2: Potential Anonymisation Locations
>
>     Anonymisation is generally performed before the wider dissemination
>     or repurposing of a flow data set, e.g., adapting operational
>     measurement data for research.  Therefore, direct anonymisation of
>     flow data on initial export is only applicable in certain restricted
>     circumstances: when the Exporting Process is "publishing" data to a
>     Collecting Process directly, and the Exporting Process and Collecting
>     Process are operated by different entities.  Note that certain
>     guidelines in Section 7.2.3 with respect to timestamp anonymisation
>     may not apply in this case, as the Collecting Process may be able to
>     deduce certain timing information from the time at which each Message
>    
IPFIX Message
>     is received.
>
>     A much more flexible arrangement is to anonymise data within a
>     Mediator [I-D.ietf-ipfix-mediators-framework].  Here, original data
>     is sent to a Mediator, which performs the anonymisation function and
>     re-exports the anonymised data.  Such a Mediator could be located at
>     the administrative domain boundary of the initial Exporting Process
>     operator, exporting anonymised data to other consumers outside the
>     organisation.  In this case, the original Exporter SHOULD use TLS as
>     specified in [RFC5101] to secure the channel to the Mediator, and the
>     Mediator should follow the guidelines in Section 7.2, to mitigate the
>
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>
>     risk of original data disclosure.
>
>     When data is to be published as an anonymised data set in an IPFIX
>     File [RFC5655], the anonymisation may be done at the final Collecting
>     Process before storage and dissemination, as well.
For me, it's a different problem. IPFIX File could be done on routers.
Basically, this paragraph is about the relationship with IPFIX File.
Btw, we're alos missing the relationship with reducing redundancy, with 
IPFIX structured data
For the later, does it apply to all instances of a template? So, some 
kind of recursivity is implied
>   In this case, the
>     Collector should follow the guidelines in Section 7.2, especially as
>     regards File-specific Options in Section 7.2.4
>
>     In each of these data flows, the anonymisation of records is
>     undertaken by an Intermediate Anonymisation Process (IAP); the data
>     flows into and out of this IAP are shown in Figure 3 below.
>
>     packets --+                     +- IPFIX Messages -+
>               |                     |                  |
>               V                     V                  V
>     +==================+ +====================+ +=============+
>     | Metering Process | | Collecting Process | | File Reader |
>     +==================+ +====================+ +=============+
>               |      Non-anonymised | Records          |
>               V                     V                  V
>     +=========================================================+
>     |          Intermediate Anonymisation Process (IAP)       |
>     +=========================================================+
>               | Anonymised     ^            Anonymised |
>               | Records        |               Records |
>               V                |                       V
>     +===================+    Anonymisation      +=============+
>     | Exporting Process |<--- Parameters ------>| File Writer |
>     +===================+                       +=============+
>               |                                        |
>               +------------>  IPFIX Messages<----------+
>
>            Figure 3: Data flows through the anonymisation process
>    
This is exactly what I was hoping to see in figure1, i.e. this draft 
applying to the Intermediate Process in [IFPIX-MD-FMWK]
... where the IP can be an independent boxe, or inside the router.
I completely missed that second part in the draft.
>     Anonymisation parameters must also be available to the Exporting
>     Process and/or File Writer in order to ensure header data is also
>     appropriately anonymised as in Section 7.2.3.
>
>     Following each of the data flows through the IAP, we describe five
>     basic types of anonymisation arrangements within this framework in
>     Figure 4.  In addition to the three arrangements described in detail
>     above, anonymisation can also be done at a collocated Metering
>     Process and File Writer (see section 7.3.2 of [RFC5655]), or at a
>     file manipulator (see section 7.3.7 of [RFC5655]).
>
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>
>           +----+  +-----+  +----+
>   pkts ->  | MP |->| IAP |->| EP |->  anonymisation on Original Exporter
>           +----+  +-----+  +----+
>           +----+  +-----+  +----+
>   pkts ->  | MP |->| IAP |->| FW |->  Anonymising collocated MP/File Writer
>           +----+  +-----+  +----+
>           +----+  +-----+  +----+
> IPFIX ->  | CP |->| IAP |->| EP |->  Anonymising Mediator (Masquerading Proxy)
>           +----+  +-----+  +----+
>           +----+  +-----+  +----+
> IPFIX ->  | CP |->| IAP |->| FW |->  Anonymising collocated CP/File Writer
>           +----+  +-----+  +----+
>           +----+  +-----+  +----+
> IPFIX ->  | FR |->| IAP |->| FW |->  Anonymising file manipulator
>   File    +----+  +-----+  +----+
>
>          Figure 4: Possible anonymisation arrangements in the IPFIX
>                                 architecture
>
>     Note that anonymisation may occur at more than one location within a
>     given collection infrastructure, to provide varying levels of
>     anonymisation, disclosure risk, or data utility for specific
>     purposes.
>
> 7.2.  IPFIX-Specific Anonymisation Guidelines
>
>     In implementing and deploying the anonymisation techniques described
>     in this document, implementors should note that IPFIX already
>     provides features that support anonymised data export, and use these
>     where appropriate.  Care must also be taken that data structures
>     supporting the operation of the protocol itself do not leak data that
>     could be used to reverse the anonymisation applied to the flow data.
>     Such data structures may appear in the header, or within the data
>     stream itself, especially as options data.  Each of these and their
>     impact on specific anonymisation techniques is noted in a separate
>     subsection below.
>
> 7.2.1.  Appropriate Use of Information Elements for Anonymised Data
>
>     Note, as in Section 6 above, that black-marker anonymised fields
>     SHOULD NOT be exported at all; the absence of the field in a given
>     Data Set is implicitly declared by not including the corresponding
>     Information Element in the Template describing that Data Set.
>
>     When using precision degradation of timestamps, Exporting Processes
>     SHOULD export timing information using Information Elements of an
>     appropriate precision, as explained in Section 4.5 of [RFC5153].  For
>     example, timestamps measured in millisecond-level precision and
>
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>
>     degraded to second-level precision should use flowStartSeconds and
>     flowEndSeconds, not flowStartMilliseconds and flowEndMilliseconds.
>
>     When exporting anonymised data and anonymisation metadata, Exporting
>     Processes SHOULD ensure that the combination of Information Element
>     and declared anonymisation technique are compatible.  Specifically,
>     the applicable and recommended Information Element types and
>     semantics for each technique are noted in the description of the
>     anonymisationTechnique Information Element in Section 6.2.3.  In this
>     description, a timestamp is an Information Element with the data type
>     dateTimeSeconds, dataTimeMilliseconds, dateTimeMicroseconds, or
>     dateTimeNanoseconds; an address is an Information Element with the
>     data type ipv4Address, ipv6Address, or macAddress; and an identifier
>     is an Information Element with identifier data type semantics.
>     Exporting Process MUST NOT export Anonymisation Options records
>     binding techniques to Information Elements to which they are not
>     applicable, and SHOULD NOT export Anonymisation Options records
>     binding techniques to Information Elements for which they are not
>     recommended.
>
> 7.2.2.  Export of Perimeter-Based Anonymisation Policies
>
>     Data collected from a single network may require different
>     anonymisation policies for addresses internal and external to the
>     network.  For example, internal addresses could be subject to simple
>     permutation, while external addresses could be aggregated into
>     networks by truncation.  When exporting anonymised perimeter
>     bidirectional flow (biflow) data as in section 5.2 of [RFC5103], this
>     arrangement may be easily represented by specifying one technique for
>     source endpoint information (which represents the external endpoint
>     in a perimeter biflow) and one technique for destination endpoint
>     information (which represents the internal address in a perimeter
>     biflow).
>
>     However, it can also be useful to represent perimeter-based
>     anonymisation policies with unidirectional flow (uniflow), or non-
>     perimeter biflow data.  In this case, the Perimeter Anonymisation bit
>     (bit 2) in the anonymisationFlags Information Element describing the
>     anonymised address Information Elements can be set to change the
>     meaning of "source" and "destination" of Information Elements to mean
>     "external" and "internal" as with perimeter biflows, but only with
>     respect to anonymisation policies.
>
> 7.2.3.  Anonymisation of Header Data
>
>     Each IPFIX Message contains a Message Header; within this Message
>     Header are contained two fields which may be used to break certain
>     anonymisation techniques: the Export Time, and the Observation Domain
>
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>
>     ID
>
>     Export of IPFIX Messages containing anonymised timestamp data where
>     the original Export Time Message header has some relationship to the
>     anonymised timestamps SHOULD anonymise the Export Time header field
>     using an equivalent technique, if possible.  Otherwise, relationships
>     between export and flow time could be used to partially or totally
>     reverse timestamp anonymisation.
>    
What if the time is in the future, the collector would probably discard 
the information.
You might want to say which methods of 4.3.* applies.

>     The similarity in size between an Observation Domain ID and an IPv4
>     address (32 bits) may lead to a temptation to use an IPv4 interface
>     address on the Metering or Exporting Process as the Observation
>     Domain ID.  If this address bears some relation to the IP addresses
>     in the flow data (e.g., shares a network prefix with internal
>     addresses) and the IP addresses in the flow data are anonymised in a
>     structure-preserving way, then the Observation Domain ID may be used
>     to break the IP address anonymisation.  Use of an IPv4 interface
>     address on the Metering or Exporting Process as the Observation
>     Domain ID is NOT RECOMMENDED in this case.
>
> 7.2.4.  Anonymisation of Options Data
>
>     IPFIX uses the Options mechanism to export, among other things,
>     metadata about exported flows and the flow collection infrastructure.
>     As with the IPFIX Message Header, certain Options recommended in
>     [RFC5101] and [RFC5655] containing flow timestamps and network
>     addresses of Exporting and Collecting Processes may be used to break
>     certain anonymisation techniques; care should be taken while using
>     them with anonymised data export and storage.
>
>     The Exporting Process Reliability Statistics Options Template,
>     recommended in [RFC5101], contains an Exporting Process ID field,
>     which may be an exportingProcessIPv4Address Information Element or an
>     exportingProcessIPv6Address Information Element.  If the Exporting
>     Process address bears some relation to the IP addresses in the flow
>     data (e.g., shares a network prefix with internal addresses) and the
>     IP addresses in the flow data are anonymised in a structure-
>     preserving way, then the Exporting Process address may be used to
>     break the IP address anonymisation.  Exporting Processes exporting
>     anonymised data in this situation SHOULD mitigate the risk of attack
>     either by omitting Options described by the Exporting Process
>     Reliability Statistics Options Template, or by anonymising the
>     Exporting Process address using a similar technique to that used to
>     anonymise the IP addresses in the exported data.
>
>     Similarly, the Export Session Details Options Template and Message
>     Details Options Template specified for the IPFIX File Format
>     [RFC5655] may contain the exportingProcessIPv4Address Information
>
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>
>     Element or the exportingProcessIPv6Address Information Element to
>     identify an Exporting Process from which a flow record was received,
>     and the collectingProcessIPv4Address Information Element or the
>     collectingProcessIPv6Address Information Element to identify the
>     Collecting Process which received it.  If the Exporting Process or
>     Collecting Process address bears some relation to the IP addresses in
>     the flow data (e.g., shares a network prefix with internal addresses)
>     and the IP addresses in the flow data are anonymised in a structure-
>     preserving way, then the Exporting Process or Collecting Process
>     address may be used to break the IP address anonymisation.  Since
>     these Options Templates are primarily intended for storing IPFIX
>     Transport Session data for auditing, replay, and testing purposes, it
>     is NOT RECOMMENDED that storage of anonymised data include these
>     Options Templates in order to mitigate the risk of attack.
>
>     The Message Details Options Template specified for the IPFIX File
>     Format [RFC5655] also contains the collectionTimeMilliseconds
>     Information Element.  As with the Export Time Message Header field,
>     if the exported flow data contains anonymised timestamp information,
>     and the collectionTimeMilliseconds Information Element in a given
>     Message has some relationship to the anonymised timestamp
>     information, then this relationship can be exploited to reverse the
>     timestamp anonymisation.  Since this Options Template is primarily
>     intended for storing IPFIX Transport Session data for auditing,
>     replay, and testing purposes, it is NOT RECOMMENDED that storage of
>     anonymised data include this Options Template in order to mitigate
>     the risk of attack.
>
>     Since the Time Window Options Template specified for the IPFIX File
>     Format [RFC5655] refers to the timestamps within the flow data to
>     provide partial table of contents information for an IPFIX File, care
>     must be taken to ensure that Options described by this template are
>     written using the anonymised timestamps instead of the original ones.
>    
Is there something in the IPFIX-MIB or IPFIX-CONF that can be used to 
deduce something about the anonymization technique?
> 7.2.5.  Special-Use Address Space Considerations
>
>     When anonymising data for transport or storage using IPFIX containing
>     anonymised IP addresses, and the analysis purpose permits doing so,
>     it is recommended to filter out or leave unanonymised data containing
>     the special-use IPv4 addresses enumerated in [RFC3330] or the
>     special-use IPv6 addresses enumerated in [RFC5153].  Data containing
>     these addresses (e.g. 0.0.0.0 and 169.254.0.0/16 for link-local
>     autoconfiguration in IPv4 space) are often associated with specific,
>     well-known behavioral patterns.  Detection of these patterns in
>     anonymised data can lead to deanonymisation of these special-use
>     addresses, which increases the chance of a complete reversal of
>     anonymisation by an attacker, especially of prefix-preserving
>     techniques.
>
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>
> 8.  Examples
>    
A nice to have would be the flow records before and after the anonymization.
>     In this example, consider the export or storage of an anonymised IPv4
>     dataset from a single network described by a simple template
>     containing a timestamp in seconds, a five-tuple, and packet and octet
>     counters.  The template describing each record in this dataset is
>     shown in figure Figure 5.
>
>                              1                   2                   3
>          0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         |          Set ID = 2           |          Length =  40         |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         |      Template ID = 256        |        Field Count = 8        |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         |0| flowStartSeconds        150 |       Field Length =  4       |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         |0| sourceIPv4Address         8 |       Field Length =  4       |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         |0| destinationIPv4Address   12 |       Field Length =  4       |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         |0| sourceTransportPort       7 |       Field Length =  2       |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         |0| destinationTransportPort 11 |       Field Length =  2       |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         |0| packetDeltaCount          2 |       Field Length =  4       |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         |0| octetDeltaCount           1 |       Field Length =  4       |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         |0| protocolIdentifier        4 |       Field Length =  1       |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
>                        Figure 5: Example Flow Template
>
>     Suppose that this dataset is anonymised according to the following
>     policy:
>
>     o  IP addresses within the network are protected by reverse
>        truncation.
>
>     o  IP addresses outside the network are protected by prefix-
>        preserving anonymisation.
>
>     o  Octet counts are exported using degraded precision in order to
>        provide minimal protection against fingerprinting attacks.
>
>     o  All other fields are exported unanonymised.
>
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>
>     In order to export anonymisation records for this template and
>     policy, first, the Anonymisation Options Template shown in figure
>     Figure 6 is exported.  For this example, the optional
>     privateEnterpriseNumber and informationElementIndex Information
>     Elements are omitted, because they are not used.
>
>                                1                   2                   3
>            0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>           |          Set ID = 3           |          Length =  26         |
>           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>           |      Template ID = 257        |        Field Count = 4        |
>           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>           |    Scope Field Count = 2      |0| templateID              346 |
>           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>           |       Field Length = 2        |0| informationElementId    303 |
>           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>           |       Field Length = 2        |0| anonymisationFlags      339 |
>           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>           |       Field Length = 2        |0| anonymisationTechnique  344 |
>           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>           |       Field Length = 2        |
>           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
>               Figure 6: Example Anonymisation Options Template
>
>     Following the Anonymisation Options Template comes a Data Set
>     containing Anonymisation Records.  This data set has an entry for
>     each Information Element Specifier in Template 256 describing the
>     flow records.  This Data Set is shown in figure Figure 7.  Note that
>     sourceIPv4Address and destinationIPv4Address have the Perimeter
>     Anonymisation (0x0004) flag set in anonymisationFlags, meaning that
>     source address should be treated as network-external, and the
>     destination address as network-internal.
>
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>
>                              1                   2                   3
>          0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         |          Set ID = 257         |          Length =  68         |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         |          Template 256         | flowStartSeconds       IE 150 |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         | no flags               0x0000 | Not Anonymised              1 |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>    
Maybe I missed it, but is there a specification in this document that 
expresses: MUST have a record for each IE of a template, even if no 
anonymization is applied.
Is there a specification that expresses: MUST have a record for each IE 
of each template, even if no IE of a particular template is anonymized.

>         |          Template 256         | sourceIPv4Address        IE 8 |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         | Perimeter, Session SC 0x0005  | Structured Permutation      6 |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         |          Template 256         | destinationIPv4Address  IE 12 |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         | Perimeter, Stable     0x0005  | Reverse Truncation          7 |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         |          Template 256         | sourceTransportPort      IE 7 |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         | no flags               0x0000 | Not Anonymised              1 |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         |          Template 256         | dest.TransportPort      IE 11 |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         | no flags               0x0000 | Not Anonymised              1 |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         |          Template 256         | packetDeltaCount         IE 2 |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         | no flags               0x0000 | Not Anonymised              1 |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         |          Template 256         | octetDeltaCount          IE 1 |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         | Stable                 0x0003 | Precision Degradation       2 |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         |          Template 256         | protocolIdentifier      IE 4  |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>         | no flags               0x0000 | Not Anonymised              1 |
>         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
>                    Figure 7: Example Anonymisation Records
>
>     Following the Anonymisation Records come the data sets containing the
>     anonymised data, exported according to the template in figure
>     Figure 5
>
> 9.  Security Considerations
>
>     This document provides guidelines for exporting metadata about
>
> Boschi&  Trammell        Expires August 19, 2010               [Page 33]
> Internet-Draft        IP Flow Anonymisation Support        February 2010
>
>     anonymised data in IPFIX, or storing metadata about anonymised data
>     in IPFIX Files.  It is not intended as a general statement on the
>     applicability of specific flow data anonymisation techniques.
>     Exporters or publishers of anonymised data must take care that the
>     applied anonymisation technique is appropriate for the data source,
>     the purpose, and the risk of deanonymisation of a given application.
>
>     We note specifically that anonymisation is not a replacement for
>     encryption for confidentiality.  It is only appropriate for
>     protecting identifying information in data to be used for purposes in
>     which the protected data is irrelevant.  Confidentiality in export is
>     best served by using TLS or DTLS as in the Security Considerations
>     section of [RFC5101], and in long-term storage by implementation-
>     specific protection applied as in the Security Considerations section
>     of [RFC5655].  Indeed, confidentiality and anonymisation are not
>     mutually exclusive, as encryption for confidentiality may be applied
>     to anonymised data export or storage, as well, when the anonymised
>     data is not intended for public release.
>
>     When using pseudonymisation techniques that have a mutable mapping,
>     there is an inherent tradeoff in the stability of the map between
>     long-term comparability and security of the dataset against
>     deanonymisation.  In general, deanonymisation attacks are more
>     effective given more information, so the longer a given mapping is
>     valid, the more information can be applied to deanonymisation.  The
>     specific details of this are technique-dependent and therefore out of
>     the scope of this document.
>
>     When releasing anonymised data, publishers need to ensure that data
>     that could be used in deanonymisation is not leaked through the
>     export protocol; guidelines for addressing this risk are provided in
>     Section 7.2.
>
>     Note as well that the Security Considerations section of [RFC5101]
>     applies as well to the export of anonymised data, and the Security
>     Considerations section of [RFC5655] to the storage of anonymised
>     data, or the publication of anonymised traces.
>
> 10.  IANA Considerations
>
>     This document specifies the creation of several new IPFIX Information
>     Elements in the IPFIX Information Element registry located at
>     http://www.iana.org/assignments/ipfix, as defined in Section 6.2
>     above.  IANA has assigned the following Information Element numbers
>     for their respective Information Elements as specified below:
>
> Boschi&  Trammell        Expires August 19, 2010               [Page 34]
> Internet-Draft        IP Flow Anonymisation Support        February 2010
>
>     o  Information Element number TBD1 for the anonymisationFlags
>        Information Element.
>
>     o  Information Element number TBD2 for the anonymisationTechnique
>        Information Element.
>
>     o  Information Element number TBD3 for the informationElementIndex
>        Information Element.
>
>     [NOTE for IANA: The text TBDn should be replaced with the respective
>     assigned Information Element numbers where they appear in this
>     document.]
>
> 11.  Acknowledgments
>
>     We thank Paul Aitken and John McHugh for their comments and insight,
>     and Carsten Schmoll for his review.  Special thanks to the ICT-PRISM
>     project for its material support of this work.
>
> 12.  References
>
> 12.1.  Normative References
>
>     [RFC5101]  Claise, B., "Specification of the IP Flow Information
>                Export (IPFIX) Protocol for the Exchange of IP Traffic
>                Flow Information", RFC 5101, January 2008.
>
>     [RFC5102]  Quittek, J., Bryant, S., Claise, B., Aitken, P., and J.
>                Meyer, "Information Model for IP Flow Information Export",
>                RFC 5102, January 2008.
>
>     [RFC5610]  Boschi, E., Trammell, B., Mark, L., and T. Zseby,
>                "Exporting Type Information for IP Flow Information Export
>                (IPFIX) Information Elements", RFC 5610, July 2009.
>
>     [RFC5655]  Trammell, B., Boschi, E., Mark, L., Zseby, T., and A.
>                Wagner, "Specification of the IP Flow Information Export
>                (IPFIX) File Format", RFC 5655, October 2009.
>
>     [RFC3330]  IANA, "Special-Use IPv4 Addresses", RFC 3330,
>                September 2002.
>
> 12.2.  Informative References
>
>     [RFC5103]  Trammell, B. and E. Boschi, "Bidirectional Flow Export
>                Using IP Flow Information Export (IPFIX)", RFC 5103,
>
> Boschi&  Trammell        Expires August 19, 2010               [Page 35]
> Internet-Draft        IP Flow Anonymisation Support        February 2010
>
>                January 2008.
>
>     [RFC5472]  Zseby, T., Boschi, E., Brownlee, N., and B. Claise, "IP
>                Flow Information Export (IPFIX) Applicability", RFC 5472,
>                March 2009.
>
>     [RFC5470]  Sadasivan, G., Brownlee, N., Claise, B., and J. Quittek,
>                "Architecture for IP Flow Information Export", RFC 5470,
>                March 2009.
>
>     [I-D.ietf-ipfix-mediators-framework]
>                Kobayashi, A., Claise, B., and K. Ishibashi, "IPFIX
>                Mediation: Framework",
>                draft-ietf-ipfix-mediators-framework-04 (work in
>                progress), October 2009.
>
>     [I-D.ietf-ipfix-mediators-problem-statement]
>                Kobayashi, A., Claise, B., Nishida, H., Sommer, C.,
>                Dressler, F., and E. Stephan, "IPFIX Mediation: Problem
>                Statement",
>                draft-ietf-ipfix-mediators-problem-statement-07 (work in
>                progress), December 2009.
>
>     [RFC5153]  Boschi, E., Mark, L., Quittek, J., Stiemerling, M., and P.
>                Aitken, "IP Flow Information Export (IPFIX) Implementation
>                Guidelines", RFC 5153, April 2008.
>
>     [RFC3917]  Quittek, J., Zseby, T., Claise, B., and S. Zander,
>                "Requirements for IP Flow Information Export (IPFIX)",
>                RFC 3917, October 2004.
>
>     [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
>                Requirement Levels", BCP 14, RFC 2119, March 1997.
>
> Authors' Addresses
>
>     Elisa Boschi
>     Hitachi Europe
>     c/o ETH Zurich
>     Gloriastrasse 35
>     8092 Zurich
>     Switzerland
>
>     Phone: +41 44 632 70 57
>     Email:[email-masked]
>
> Boschi&  Trammell        Expires August 19, 2010               [Page 36]
> Internet-Draft        IP Flow Anonymisation Support        February 2010
>
>     Brian Trammell
>     Hitachi Europe
>     c/o ETH Zurich
>     Gloriastrasse 35
>     8092 Zurich
>     Switzerland
>
>     Phone: +41 44 632 70 13
>     Email:[email-masked]
>
> Boschi&  Trammell        Expires August 19, 2010

---

From: Brian Trammell <[email-masked]>
Date: Thu, 8 Apr 2010 11:46:51 +0200

hi, Benoit,

thank you very much for the review! Comments inline, irrelevant parts snipped. These changes will be applied to future anon-03, which will appear after we get Lothar's WGLC comments.

Cheers,

Brian

>>                       draft-ietf-ipfix-anon-02.txt

<snip>

>> Boschi & Trammell        Expires August 19, 2010                [Page 5]
>>    ||| Picking/sending Flow Records|->|  & data Information into   ||  |
>>    ||| Encoding Template & data    |  |  IPFIX export packets.     ||  |
>> Boschi & Trammell        Expires August 19, 2010                [Page 6]

Indeed. This is a restatement of a part of 5470, intended mainly to provide background for why anonymisation support is crucial for IPFIX. However, the diagram is as you point out kind of confusing here. Its primary function is to frame the work within the larger, longer work of the WG.. which we do in the paragraph below anyway. So we're inclined to cut it.

> If the reference model was from the IPFIX Mediator framework, then we would not have the issue with optional.

Yes. This reference should be here (instead of "original architecture specification").

> It would be nice to say in the terminology section which terms you use from other RFCs.

This is an unfortunate consequence of IPFIX having something called a "Data Set". We need a term within this WG that means "some data" but that does not conflict with the defined terminology. Suggestions?

> For example, flow records is lower case, but I see IPFIX File, Options Template

Will review. Indeed, here "messages" should be "Messages", however, this sentence may need to be rewritten anyway, because IPFIX Mediators don't rewrite Messages (in the general case) as defined.

>>    Anonymisation modifies a data set in order to protect the identity of

Here is a perfect example of the point above. This is "some data", not an IPFIX Data Set. Can we agree that "data set" is not "Data Set", or should we invent some more terminology here?

>>    data cannot be traced back to the specific networks, hosts, or users

<snip>

>> 4.  Anonymisation of IP Flow Data

<snip>

> I would clearly mention MAC address

Okay... will s/hardware address/MAC address/gi then.

>>    continent (or RIR region of responsibility).

Regional Internet Registry [RFC1466], [RFC2050]. Shall we add these as informatives, or drop the reference to RIRs?

<snip>

>>    Presice timestamps can be used in injected-traffic fingerprinting

Oops. An embarrassing word to typo. :)

> Yo might want to describe what fingerprinting is

Will do.

> it's like truncation, but specific to time and counter, right?

Truncation is for identifiers, precision degradation is for numbers, but yes. This is why they have the same anon technique number in metadata export.

<snip>

>> Boschi & Trammell        Expires August 19, 2010               [Page 16]

will normalize these

> metadata about exported flows and the flow collection infrastructure

but this one means something different (anon metadata = "what are the properties of the anonymisation applied to this data?", while this is "anything in an options record (that might be useful to deanonymisation)").

> You might want to be consistent

Perhaps, yes. ;) Will fix these, definitely.

> In this section, you don't say if you must export the content of this section, while you do for all the other 5.x sections

Good point. Will mention this (i.e., that we SHOULD).

<snip>

>>    anonymised fields SHOULD NOT be exported at all; the absence of the

A MUST NOT here would conflict with the parallel guidance in RFC 5103 (section 4, para 6, page 7) regarding empty reverse IEs (SHOULD not), and in the configuration draft, which allows fields which can be unambiguously null in context to be exported as null (MAY). What about anonymisation in an environment with hardcoded templates? No reason to take freedom away from implementors in this situation. 

> an anonymization record is actually a data record of the Anonymization Options Template Record, as opposed to an anonymized record.

Yep. So "Anonymisation Record" and "Anonymised Data Record" will go into terminology then.

>> Boschi & Trammell        Expires August 19, 2010               [Page 18]
> Otherwise, if the collector doesn't have received the anonimization records, then it might be treating the flow records wrongly.

Yeah, but only if per-stream is anyway compatible with the underlying application. Worth a mention and an informative reference, probably.

> Isn't it privateEnterpriseNumber instead of informationElementId?

Yep, typo. Will fix.

> However, I'm wondering why you need this privateEnterpriseNumber at all,  because the "E" bit is already part of informationElementId 
>  0                   1                   2                   3

The enterprise bit only says that it's got a PEN, not what the PEN is, so we still need it.

>> Boschi & Trammell        Expires August 19, 2010               [Page 19]

<snip>

>> Boschi & Trammell        Expires August 19, 2010               [Page 20]

See section 7.2.2. If we still need to clarify here, we can.

>>    |        |          | ignored by the Collecting Process.            |

<snip>

> While reading, it looks more logical to have the anonymisationTechnique before the anonymizationFlags IE

For IEs, the sections in the document (as in 5610, 5655) are alphabetized by IE name. However, you're right, it makes more sense to do them in "logical" order when there aren't so many of them.

> And options template as well? For example, in my company, we export a options template record with the sampling rates.

Absolutely. Will add.

>>       these restrictions are noted in the table below.

<snip>

>> 7.1.  Arrangement of Processes in IPFIX Anonymisation

<snip>

> Basically, this paragraph is about the relationship with IPFIX File.

Mainly because this section is about the arrangement of processes, and a File Writer is something 

> Btw, we're alos missing the relationship with reducing redundancy

I'm not sure I get what's special about reducing redundancy with respect to anon.

> with IPFIX structured data
> For the later, does it apply to all instances of a template? So, some kind of recursivity is implied

This is probably something that should be addressed in Structured Data (the only hard question here is how meta-template information is handled with basicList) as opposed to the other way around, because of the chronology, and because anon is not the only meta-template we may have to address. In general we should avoid normative references that go forward in time...

Since this is metatemplate information, it should be stored by the CP as if it belongs to the template. So, yes, it applies to any instance of an template active at the time. This implies that we should point out somewhere that this information expires when the template is withdrawn or expires (ouch!).

>>              +------------> IPFIX Messages <----------+
>> 
> This is exactly what I was hoping to see in figure1, i.e. this draft applying to the Intermediate Process in [IFPIX-MD-FMWK]

Another reason simply to drop figure 1.

>>    file manipulator (see section 7.3.7 of [RFC5655]).

<snip>

>> Boschi & Trammell        Expires August 19, 2010               [Page 28]
> What if the time is in the future, the collector would probably discard the information.

Why? This seems highly implementation dependent.

> You might want to say which methods of 4.3.* applies. 

Good point.

<snip>
>> 7.2.4.  Anonymisation of Options Data

<snip>

> Is there something in the IPFIX-MIB or IPFIX-CONF that can be used to deduce something about the anonymization technique?

Not that would be exported, no. If the device supports configuration extensions for anonymisation, clearly you shouldn't export that, but it's also out of band, so not really applicable here.

<snip>

> A nice to have would be the flow records before and after the anonymization.

Yep. A fair amount of extra work, but, yep, completely agree. 

<snip>

> Maybe I missed it, but is there a specification in this document that expresses: MUST have a record for each IE of a template, even if no anonymization is applied.
> Is there a specification that expresses: MUST have a record for each IE of each template, even if no IE of a particular template is anonymized.

Nope. If an IE in a template isn't specified, it's "default" which is "maybe not anonymized, but we don't really know." We'll clarify this above.

---

From: Benoit Claise <[email-masked]>
Date: Mon, 12 Apr 2010 17:12:59 +0200

Hi Brian,
> This is an unfortunate consequence of IPFIX having something called a "Data Set". We need a term within this WG that means "some data" but that does not conflict with the defined terminology. Sugge…
If you have a terminology section, including Data Set, that would solve 
it. It would be clear what data set would (not) be.
> Here is a perfect example of the point above. This is "some data", not an IPFIX Data Set. Can we agree that "data set" is not "Data Set", or should we invent some more terminology here?
See my point above.
> A MUST NOT here would conflict with the parallel guidance in RFC 5103 (section 4, para 6, page 7) regarding empty reverse IEs (SHOULD not), and in the configuration draft, which allows fields which…

I'm unclear how black-marker fields should be exported: with zero-length 
(bad idea, because 0 might mean something else) or with zero (in that 
case, we lose some bandwidth for all Flow Records)?
Also I was wondering if we could have an Anonymization Options Template 
for a field that does not appear in the Template Record?
Maybe clarify the points first
Whatever you specify, this must be inline with RFC5101:

    If a specific Information Element is required by a Template, but is
    not available in observed packets, the Exporting Process MAY choose
    to export Flow Records without this Information Element in a Data
    Record defined by a new Template.

> The enterprise bit only says that it's got a PEN, not what the PEN is, so we still need it.

I was thinking that informationElementId would contain the E bit. 
Checking with RFC5610 and IPFIX IANA, this is not the case.
This should be clarified.
Also expresses the two cases where this is needed.
1. two different PENs with the same informationElementId
2. One PEN and one non PEN with the same informationElementId

> This is probably something that should be addressed in Structured Data (the only hard question here is how meta-template information is handled with basicList) as opposed to the other way around, b…
Agreed on the last point.
> Since this is metatemplate information, it should be stored by the CP as if it belongs to the template. So, yes, it applies to any instance of an template active at the time. This implies that we s…
Yes!
Next to the expiration and scope conditions, you might have one sentence 
such as: once the Anonymization Options Template Record is specified, 
it's valid for all instances of Flow Records conforming to this definition.
This would take care of IPFIX-RED-RED and IPFIX-STRUCT
I'm sure you will find some better wording, but you get my point.
> Why? This seems highly implementation dependent.
Sure, but it was never specified in RFC5101.
Maybe add two sentences such as:
     exporter: SHOULD NOT send in future times, due to anyonymation 
techniques
     collector, MAY accept future times in connection with Anonymization 
Options Templates , but MUST log a warning.
> Not that would be exported, no. If the device supports configuration extensions for anonymisation, clearly you shouldn't export that, but it's also out of band, so not really applicable here.

If I'm an attacker, wanting to decipher your anonymization technique, 
everything will help.
If you do support the IPFIX-MIB, PSAMP-MIB, and you use SNMPv1 or v2c, I 
can sniff the community string, and get all information in the MIBs. 
Will it help me? Maybe I'm not sure!
If I can do the same with the configuration, I might help in some cases. 
For example, in case of a permanent cache exported every hour UTC, a 
simple correlation of the time in the anoymized flow records with the 
config time will get me what I need.
So maybe a few sentences would clarify what to pay attention to.

Regards, Benoit.

---

From: Brian Trammell <[email-masked]>
Date: Wed, 14 Apr 2010 09:47:07 +0200

Hi, Benoit,

Per our telephone conversation, we've addressed these comments in the working copy of -03, which I'll submit once I've received and integrated Lothar's comments. Many thanks for your review!

Cheers,

Brian

On Apr 12, 2010, at 5:12 PM, Benoit Claise wrote:

> If you have a terminology section, including Data Set, that would solve it. It would be clear what data set would (not) be.
>>   
> I'm unclear how black-marker fields should be exported: with zero-length (bad idea, because 0 might mean something else) or with zero (in that case, we lose some bandwidth for all Flow Records)?
> Also I was wondering if we could have an Anonymization Options Template for a field that does not appear in the Template Record?
> I was thinking that informationElementId would contain the E bit. Checking with RFC5610 and IPFIX IANA, this is not the case.
> Next to the expiration and scope conditions, you might have one sentence such as: once the Anonymization Options Template Record is specified, it's valid for all instances of Flow Records conforming to this definition.
>    exporter: SHOULD NOT send in future times, due to anyonymation techniques
>    collector, MAY accept future times in connection with Anonymization Options Templates , but MUST log a warning.
>> 
>>   
> If I'm an attacker, wanting to decipher your anonymization technique, everything will help.
> If you do support the IPFIX-MIB, PSAMP-MIB, and you use SNMPv1 or v2c, I can sniff the community string, and get all information in the MIBs. Will it help me? Maybe I'm not sure!
> If I can do the same with the configuration, I might help in some cases. For example, in case of a permanent cache exported every hour UTC, a simple correlation of the time in the anoymized flow records with the config time will get me what I need.