





Internet Engineering Task Force (IETF)                       I. McDonald
Request for Comments: 7472                              High North, Inc.
Updates: 2910, 2911                                             M. Sweet
Category: Standards Track                                    Apple, Inc.
ISSN: 2070-1721                                               March 2015


     Internet Printing Protocol (IPP) over HTTPS Transport Binding
                       and the 'ipps' URI Scheme

Abstract

   This document defines the Internet Printing Protocol (IPP) over HTTPS
   transport binding and the corresponding 'ipps' URI scheme, which is
   used to designate the access to the network location of a secure IPP
   print service or a network resource managed by such a service.

   This document defines an alternate IPP transport binding to that
   defined in the original IPP URL Scheme (RFC 3510), but this document
   does not update or obsolete RFC 3510.

   This document updates RFCs 2910 and 2911.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7472.















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Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   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
   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

























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Table of Contents

   1. Introduction ....................................................3
      1.1. Structure of This Document .................................4
      1.2. Rationale for This Document ................................5
   2. Conventions Used in This Document ...............................5
      2.1. Requirements Language ......................................5
      2.2. Printing Terminology .......................................5
      2.3. Abbreviations ..............................................6
   3. IPP over HTTPS Transport Binding ................................7
   4. Definition of 'ipps' URI Scheme .................................8
      4.1. Applicability of 'ipps' URI Scheme .........................8
      4.2. Syntax of 'ipps' URI Scheme ................................8
      4.3. Associated Port for 'ipps' URI Scheme .....................10
      4.4. Character Encoding of 'ipps' URI Scheme ...................10
      4.5. Examples of 'ipps' URIs ...................................11
      4.6. Comparisons of 'ipps' URIs ................................12
   5. IANA Considerations ............................................12
   6. Security Considerations ........................................13
      6.1. Problem Statement .........................................13
           6.1.1. Targets of Attacks .................................14
           6.1.2. Layers of Attacks ..................................14
      6.2. Attacks and Defenses ......................................14
           6.2.1. Faked 'ipps' URI ...................................15
           6.2.2. Unauthorized Access by IPP Client ..................15
           6.2.3. Compromise at Application Layer Gateway ............15
           6.2.4. No Client Authentication for 'ipps' URI ............15
      6.3. TLS Version Requirements ..................................16
   7. References .....................................................16
      7.1. Normative References ......................................16
      7.2. Informative References ....................................17
   Acknowledgments ...................................................19
   Authors' Addresses ................................................19

1.  Introduction

   This document defines the Internet Printing Protocol (IPP) over HTTPS
   transport binding and the corresponding 'ipps' URI scheme, which is
   used to designate the access to the network location of a secure IPP
   print service or a network resource managed by such a service.

   This document has been submitted to the IETF by the Internet Printing
   Protocol Working Group (WG) of the IEEE-ISTO Printer Working Group,
   as part of their PWG "IPP Everywhere" (PWG 5100.14) project for
   secure mobile printing with vendor-neutral Client software.






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   This document defines an alternate IPP transport binding to that
   defined in the original IPP URL Scheme [RFC3510], but this document
   does not update or obsolete [RFC3510].

   This document updates:

   a) "Internet Printing Protocol/1.1: Encoding and Transport"
      [RFC2910], by extending Section 4 ("Encoding of Transport Layer"),
      Section 5 ("IPP URL Scheme"); and Section 8.2 ("Using IPP with
      TLS") to add the new standard URI scheme of 'ipps' for IPP
      Printers; and

   b) "Internet Printing Protocol/1.1: Model and Semantics" [RFC2911],
      by extending Section 4.1.6 ("uriScheme") and Section 4.4.1
      ("printer-uri-supported") to add the new standard URI scheme of
      'ipps' for IPP Printers.

   The following versions of IPP are currently defined:

      a) 1.0 in [RFC2566] (obsolete);
      b) 1.1 in [RFC2911];
      c) 2.0 in [PWG5100.12];
      d) 2.1 in [PWG5100.12]; and
      e) 2.2 in [PWG5100.12].

   Overview information about IPP is available in Section 1 of
   [RFC2911], Section 1 of [RFC3196], and Section 1 of PWG "IPP Version
   2.0 Second Edition (IPP/2.0 SE)" [PWG5100.12].

1.1.  Structure of This Document

   This document contains the following sections:

   Section 2 defines the conventions and terms used throughout the
   document.

   Section 3 defines the IPP over HTTPS transport binding.

   Section 4 defines the 'ipps' URI scheme.

   Sections 5 and 6 contain IANA and security considerations,
   respectively.

   Section 7 contains references.







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1.2.  Rationale for This Document

   The 'ipps' URI scheme was defined for the following reasons:

   1) Some existing IPP Client and IPP Printer implementations of
      "Upgrading to TLS Within HTTP/1.1" [RFC2817] are flawed and
      unreliable, although this is not due to specification defects in
      [RFC2817] itself.

   2) Some existing IPP Client and IPP Printer implementations of HTTP
      upgrade [RFC2817] do not perform an upgrade at the beginning of
      every HTTP [RFC7230] connection; instead, they only shift to
      secure IPP for selected IPP operations (inherently dangerous
      behavior on the same underlying TCP [RFC793] connection).

   3) IPP Printer server-mandated HTTP upgrade [RFC2817] can still lead
      to exposure of IPP Client data if the Expect request header is not
      used -- basically, the IPP Client can send its whole Print-Job
      request before the IPP Printer has a chance to respond and say,
      "Wait!  You need to encrypt first!".

2.  Conventions Used in This Document

2.1.  Requirements Language

   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 [RFC2119].

2.2.  Printing Terminology

   The reader of this document needs to be familiar with the printing
   terms defined in "Internet Printing Protocol/1.1: Model and
   Semantics" [RFC2911] as well as the following:

   IPP Client: The software (on some hardware platform) that submits IPP
      Job creation and IPP Printer and IPP Job management operations via
      the IPP over HTTP transport binding defined in the IPP/1.1
      Encoding and Transport document [RFC2910] and/or the IPP over
      HTTPS transport binding defined in Section 3 of this specification
      to an IPP Printer (print spooler, print gateway, or physical
      printing device).

   IPP Job:  The set of attributes and documents for one print job
      instantiated in an IPP Printer.

   IPP Job object:  Synonym for IPP Job.




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   IPP Printer: The software (on some hardware platform) that receives
      IPP Job creation and IPP Printer and IPP Job management operations
      via the IPP over HTTP transport binding defined in the IPP/1.1
      Encoding and Transport document [RFC2910] and/or the IPP over
      HTTPS transport binding defined in Section 3 of this specification
      from an IPP Client.

   IPP Printer object:  Synonym for IPP Printer.

   'ipps' URI:  A URI using the 'ipps' URI scheme defined in Section 4
      of this specification.

2.3.  Abbreviations


   This document makes use of the following abbreviations (given with
   their expanded forms and references for further reading):

   ABNF   - Augmented Backus-Naur Form [STD68]

   ASCII  - American Standard Code for Information Interchange [ASCII]

   HTTP   - HyperText Transfer Protocol [RFC7230]

   HTTPS  - HTTP over TLS [RFC7230]

   IANA   - Internet Assigned Numbers Authority
            <http://www.iana.org>

   IEEE   - Institute of Electrical and Electronics Engineers
            <http://www.ieee.org>

   IESG   - Internet Engineering Steering Group
            <http://www.ietf.org/iesg/>

   IPP    - Internet Printing Protocol [RFC2911] and [PWG5100.12]
            <http://www.pwg.org/ipp/>

   ISTO   - IEEE Industry Standards and Technology Organization
            <http://www.ieee-isto.org/>

   LPD    - Line Printer Daemon Protocol [RFC1179]

   PWG    - IEEE-ISTO Printer Working Group
            <http://www.pwg.org>

   RFC    - Request for Comments
            <http://www.rfc-editor.org>



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   TCP    - Transmission Control Protocol [RFC793]

   TLS    - Transport Layer Security [RFC5246]

   URI    - Uniform Resource Identifier [STD66]

   URL    - Uniform Resource Locator [STD66]

   UTF-8  - Unicode Transformation Format - 8-bit [STD63]

3.  IPP over HTTPS Transport Binding

   This document defines the following alternate IPP over HTTPS
   transport binding for the abstract protocol defined in "Internet
   Printing Protocol/1.1: Model and Semantics" [RFC2911] and IEEE-ISTO
   PWG "IPP Version 2.0 Second Edition (IPP/2.0 SE)" [PWG5100.12].

   When using an 'ipps' URI, an IPP Client MUST establish an IPP
   application-layer connection according to the following sequence:

   1) The IPP Client selects an 'ipps' URI value from a "printer-uri-
      supported" Printer attribute [RFC2911], a directory entry,
      discovery info, a web page, etc.;

   2) The IPP Client converts the 'ipps' URI to an 'https' URI [RFC7230]
      (replacing 'ipps' with 'https' and inserting the port number from
      the URI or port 631 if the URI doesn't include an explicit port
      number);

   3) The IPP Client establishes an HTTPS [RFC7230] secure session layer
      connection to the target endpoint; and

   4) The IPP Client sends requests to and receives responses from the
      target IPP application-layer resource over the HTTPS [RFC7230]
      secure session layer connection using the POST method defined in
      [RFC7231].















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4.  Definition of 'ipps' URI Scheme

4.1.  Applicability of 'ipps' URI Scheme

   Per PWG "IPP Everywhere" [PWG5100.14], in IPP exchanges, the 'ipps'
   URI scheme MUST only be used:

   a) To specify an absolute URI for IPP secure print services and their
      associated network resources;

   b) To specify the use of the abstract protocol defined in "Internet
      Printing Protocol/1.1: Model and Semantics" [RFC2911] and IEEE-
      ISTO PWG "IPP Version 2.0 Second Edition (IPP/2.0 SE)"
      [PWG5100.12]; and

   c) To specify the use of the transport binding defined in this
      document.

   The 'ipps' URI scheme allows an IPP Client to choose an appropriate
   IPP secure print service (for example, from a directory).  The IPP
   Client can establish an HTTPS connection to the specified IPP secure
   print service.  The IPP Client can send IPP requests (for example,
   Print-Job requests) and receive IPP responses over that HTTPS
   connection.

   See:  Section 4.2 ("Syntax of 'ipps' URI Scheme") of this document.

   See:  Section 4.4.1 ("printer-uri-supported") in [RFC2911].

   See:  Section 5 ("IPP URL Scheme") in [RFC2910].

   See:  Section 4 ("IPP Standards") of IEEE-ISTO PWG "IPP Version 2.0
         Second Edition (IPP/2.0 SE)" [PWG5100.12].

4.2.  Syntax of 'ipps' URI Scheme

   The abstract protocol defined in [RFC2911] places a limit of 1023
   octets (NOT characters) on the length of a URI.

   See:  "Uniform Resource Identifier (URI): Generic Syntax" [STD66].

   Per PWG "IPP Everywhere" [PWG5100.14], for compatibility with
   existing IPP implementations, IPP Printers SHOULD NOT generate 'ipp'
   [RFC3510] or 'ipps' URI (or allow administrators to configure)
   lengths above 255 octets, because many older IPP Client
   implementations do not properly support these lengths.





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   Per PWG "IPP Everywhere" [PWG5100.14], in IPP exchanges, 'ipps' URIs
   MUST be represented in absolute form.  Absolute URIs always begin
   with a scheme name followed by a colon.  For definitive information
   on URI syntax and semantics, see "Uniform Resource Identifier (URI):
   Generic Syntax and Semantics" [STD66].  This specification adopts the
   definitions of "host", "port", and "query" from [STD66].  This
   specification adopts the definition of "absolute-path" from
   [RFC7230].

   The 'ipps' URI scheme syntax in ABNF [STD68] is defined as follows:

   ipps-uri =
       "ipps:" "//" host [ ":" port ] [ absolute-path [ "?" query ]]

   Per [RFC2910], if the port is empty or not given, then port 631 MUST
   be used.

   See:  Section 4.3 ("Associated Port for 'ipps' URI Scheme") in this
   document.

   The semantics are that the identified resource (see [RFC7230]) is
   located at the IPP secure print service listening for HTTPS
   connections on that port of that host; and the Request-URI for the
   identified resource is 'absolute-path'.

   Note:  The higher-level "authority" production is not imported from
   [STD66], because it includes an optional "userinfo" component that
   cannot be used in 'ipps' URIs.

   Note:  The "query" production does not have defined semantics in IPP
   and was never used in examples in the IPP/1.1 Encoding and Transport
   document [RFC2910] or the original IPP URL Scheme [RFC3510].  The
   "query" is retained here for consistency, but IPP Clients SHOULD
   avoid its use (because the semantics would be implementation
   defined).

   Note:  Per PWG "IPP Everywhere" [PWG5100.14], literal IPv4 or IPv6
   addresses SHOULD NOT be used in 'ipps' URIs, because:

   a) IP addresses are often changed after network device installation
      (for example, based on DHCP reassignment after a power cycle);

   b) IP addresses often don't map simply to security domains;

   c) IP addresses are difficult to validate with X.509 server
      certificates (because they do not map to common name or alternate
      name attributes); and




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   d) IP link local addresses are not "portable" due to link identity.

   Per [RFC2910], if the 'absolute-path' is not present in an IPP URI,
   it MUST be given as "/" when used as a Request-URI for a resource
   (see [RFC7230]).  An 'ipps' URI is transformed into an 'https' URI by
   replacing "ipps:" with "https:" and inserting port 631 (if an
   explicit 'port' is not present in the original 'ipps' URI).

   See:  Section 4.3 ("Associated Port for 'ipps' URI Scheme") in this
   document.

4.3.  Associated Port for 'ipps' URI Scheme

   Per [RFC2910], all 'ipps' URIs that do NOT explicitly specify a port
   MUST be resolved to IANA-assigned well-known port 631, already
   registered in [PORTREG] by [RFC2910].

   Note:  Per direction of the IESG, as described in [RFC2910], port 631
   is used for all IPP connections (with or without TLS [RFC5246]).
   Therefore, port 631 is used for both 'ipp' [RFC3510] and 'ipps' URIs,
   which both refer to an IPP Printer or a network resource managed by
   an IPP Printer.  IPP Printer implementors can refer to the CUPS
   [CUPS] source code for an example of incoming connection handling for
   the dual use of port 631.

   See:  IANA Port Numbers Registry [PORTREG].

   See:  [RFC2910].

4.4.  Character Encoding of 'ipps' URI Scheme

   Per PWG "IPP Everywhere" [PWG5100.14], 'ipps' URIs MUST:

   a) Use the UTF-8 [STD63] charset for all components; and

   b) Use [STD66] rules for percent encoding data octets outside the US-
      ASCII-coded character set [ASCII].














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4.5.  Examples of 'ipps' URIs

   The following are examples of well-formed 'ipps' URIs for IPP
   Printers (for example, to be used as protocol elements in 'printer-
   uri' operation attributes of Print-Job request messages):

       ipps://example.com/
       ipps://example.com/ipp
       ipps://example.com/ipp/faxout
       ipps://example.com/ipp/print
       ipps://example.com/ipp/scan
       ipps://example.com/ipp/print/bob
       ipps://example.com/ipp/print/ira

   Note:  The use of an explicit 'ipp' path component followed by
   explicit 'print', 'faxout', 'scan', or other standard or vendor
   service component is best practice per [PWG5100.14], [PWG5100.15],
   and [PWG5100.17].

   Each of the above URIs is a well-formed URI for an IPP Printer and
   each would reference a logically different IPP Printer, even though
   some of those IPP Printers might share the same host system.  Note
   that 'print' might represent some grouping of IPP Printers (for
   example, a load-balancing spooler), while the 'bob' or 'ira' last
   path components might represent two different physical printer
   devices, or 'bob' and 'ira' might represent separate human recipients
   on the same physical printer device (for example, a physical printer
   supporting two job queues).  Regardless, both 'bob' and 'ira' would
   behave as different and independent IPP Printers.

   The following are examples of well-formed 'ipps' URIs for IPP
   Printers with (optional) ports and paths:

       ipps://example.com/
       ipps://example.com/ipp/print
       ipps://example.com:631/ipp/print

   The first and second 'ipps' URIs above will be resolved to port 631
   (IANA-assigned well-known port for IPP).  The second and third 'ipps'
   URIs above are equivalent (see Section 4.6).

   See:  Sections 4.2 ("Syntax of 'ipps' URI Scheme") and 4.3
   ("Associated Port for 'ipps' URI Scheme") in this document.








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4.6.  Comparisons of 'ipps' URIs

   Per PWG "IPP Everywhere" [PWG5100.14], when comparing two 'ipps' URIs
   to decide whether or not they match, an IPP Client MUST use the same
   rules as those defined for 'http' and 'https' URI comparisons in
   [RFC7230], with the following single exception:

   -  A port that is empty or not given MUST be treated as equivalent to
      the well-known port for that 'ipps' URI (port 631).

   See:  Section 4.3 ("Associated Port for 'ipps' URI Scheme") in this
         document.

   See:  Section 2.7.3 ("http and https URI Normalization and
         Comparison") in [RFC7230].

5.  IANA Considerations

   IANA has registered the new keyword value 'ipps' for the IPP Printer
   "printer-uri-supported" attribute in the IANA IPP Registry [IPPREG],
   per Section 6.2 ("Attribute Extensibility") of [RFC2911] as follows:

   IANA has registered the 'ipps' URI scheme using the following
   template, which conforms to [BCP35].

   URI scheme name:  ipps

   Status:  Permanent

   URI scheme syntax:  See Section 4.2 of RFC 7472.

   URI scheme semantics:  The 'ipps' URI scheme is used to designate
      secure IPP Printer objects (print spoolers, print gateways, print
      devices, etc.) on Internet hosts accessible using the IPP enhanced
      to support guaranteed data integrity and negotiable data privacy
      using TLS [RFC5246] as specified in HTTP/1.1 [RFC7230].

   Encoding Considerations:  See Section 4.4 of RFC 7472.

   Applications/protocols that use this URI scheme name: The 'ipps' URI
      scheme is intended to be used by applications that need to access
      secure IPP Printers using the IPP enhanced to support guaranteed
      data integrity and negotiable data privacy using TLS [RFC5246] as
      specified in HTTP/1.1 [RFC7230].  Such applications may include
      (but are not limited to) IPP-capable web browsers, IPP Clients
      that wish to print a file, and servers (for example, print
      spoolers) wishing to forward a Job for processing.




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   Interoperability Considerations: The widely deployed, open source IPP
      print service CUPS [CUPS] (on most UNIX, Linux, and Apple OS X
      systems) has supported 'ipps' URI for several years before the
      publication of this document.  PWG "IPP Everywhere" [PWG5100.14]
      (IPP secure, mobile printing extensions) requires the use of
      'ipps' URI for mandatory data integrity and negotiable data
      confidentiality.

   Security Considerations:  See Section 6 of RFC 7472.

   Contact: Ira McDonald <blueroofmusic@gmail.com>,
      Michael Sweet <msweet@apple.com>

   Author/Change controller: IESG

   References:  RFCs 2910, 2911, and 7472; IEEE-ISTO PWG 5100.12.

6.  Security Considerations

6.1.  Problem Statement

   Powerful mobile devices (laptops, tablets, smartphones, etc.) are now
   commonly used to access enterprise and Cloud print services across
   the public Internet.  This is the primary use case for PWG "IPP
   Everywhere" [PWG5100.14], which has already been adopted by operating
   system and printer vendors and several other public standards bodies.
   End-user and enterprise documents and user privacy-sensitive
   information are at greater risk than ever before.  This IPP-over-
   HTTPS transport binding and 'ipps' URI scheme specification was
   defined to enable high availability combined with secure operation in
   this dynamic environment (for example, wireless hotspots in hotels,
   airports, and restaurants).

   See:  Section 1 ("Introduction") of [PWG5100.14].

   See:  Section 3.1 ("Rationale") of [PWG5100.14].















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6.1.1.  Targets of Attacks

   A network print spooler (logical printer) or print device (physical
   printer) is potentially subject to attacks, which may target:

   a) The network (to compromise the routing infrastructure, for
      example, by creating congestion);

   b) The Internet Printing Protocol (IPP) [RFC2911] (for example, to
      compromise the normal behavior of IPP);

   c) The print job metadata (for example, to extract privacy-sensitive
      information from the job submission request or via query of the
      job on the IPP Printer); or

   d) The print document content itself (for example, to steal the data
      or to corrupt the documents being transferred).

6.1.2.  Layers of Attacks

   Attacks against print services can be launched:

   a) Against the network infrastructure (for example, TCP [RFC793]
      congestion control);

   b) Against the IPP data flow itself (for example, by sending forged
      packets or forcing TLS [RFC5246] version downgrade); or

   c) Against the IPP operation parameters (for example, by corrupting
      requested document processing attributes).

6.2.  Attacks and Defenses

   This 'ipps' URI Scheme specification adds the following additional
   security considerations to those described in [RFC7230], [RFC2910],
   [RFC2911], [RFC5246], [RFC7230], [PWG5100.12], and [STD66].

   See:  Section 8 ("Security Considerations") in [RFC2910].

   See:  Section 8 ("Security Considerations") in [RFC2911].

   See:  Appendix D ("Implementation Notes"), Appendix E ("Backward
         Compatibility"), and Appendix F ("Security Analysis") of
         [RFC5246].

   See:  Section 10 ("Security Considerations") in [PWG5100.12].

   See:  Section 7 ("Security Considerations") in [STD66].



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6.2.1.  Faked 'ipps' URI

   An 'ipps' URI might be faked to point to a rogue IPP secure print
   service, thus collecting confidential job metadata or document
   contents from IPP Clients.

   Due to administrator reconfiguration or physical relocation of an IPP
   Printer, a former literal IPv4 or IPv6 address might no longer be
   valid.  See Section 4.2 ("Syntax of 'ipps' URI Scheme") for the
   recommendation against the use of literal IP addresses in 'ipps' URI.

   Server authentication mechanisms and security mechanisms specified in
   IPP/1.1 Encoding and Transport [RFC2910], HTTP/1.1 [RFC7230], and
   TLS/1.2 [RFC5246] can be used to address this threat.

6.2.2.  Unauthorized Access by IPP Client

   An 'ipps' URI might be used to access an IPP secure print service by
   an unauthorized IPP Client, for example, extracting privacy-sensitive
   information such as "job-originating-user-name" job metadata defined
   in [RFC2911].

   Client authentication mechanisms and security mechanisms specified in
   IPP/1.1 Encoding and Transport [RFC2910], HTTP/1.1 [RFC7230], and
   TLS/1.2 [RFC5246] can be used to address this threat.

6.2.3.  Compromise at Application Layer Gateway

   An 'ipps' URI might be used to access an IPP secure print service at
   a print protocol application layer gateway (for example, an IPP to
   LPD [RFC1179] gateway [RFC2569]), potentially causing silent
   compromise of IPP security mechanisms.

   There is no general defense against this threat by an IPP Client.
   System administrators SHOULD avoid such configurations.

6.2.4.  No Client Authentication for 'ipps' URI

   An 'ipps' URI does not define parameters to specify the required IPP
   Client authentication mechanism (for example, 'certificate' as
   defined in Section 4.4.2 ("uri-authentication-supported") of
   [RFC2911]).

   An IPP Client SHOULD first use service discovery or directory
   protocols (e.g., the "Lightweight Directory Access Protocol (LDAP):
   Schema for Printer Services" [RFC3712]) or directly send an IPP Get-
   Printer-Attributes operation to the target IPP Printer to read




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   "printer-uri-supported", "uri-authentication-supported", and "uri-
   security-supported" attributes to discover the required IPP Client
   authentication and security mechanisms for each supported URI.

6.3.  TLS Version Requirements

   Per PWG "IPP Everywhere" [PWG5100.14] (and in accordance with
   security best practices and all existing deployments of the 'ipps'
   URI scheme), IPP Clients and IPP Printers that support this
   specification MUST use TLS/1.2 [RFC5246] or a higher version, for all
   'ipps' secure transport layer connections.

   Implementors will find useful advice in the "Recommendations for
   Secure Use of TLS and DTLS" [TLSBCP].

7.  References

7.1.  Normative References

   [ASCII]      American National Standards Institute, "Coded Character
                Set -- 7-bit American Standard Code for Information
                Interchange", ANSI X3.4, 1986.

   [PWG5100.12] Bergman, R., Lewis, H., McDonald, I., and M. Sweet,
                "Internet Printing Protocol", Version 2.0, Second
                Edition (IPP/2.0 SE), PWG 5100.12, February 2011,
                <http://www.pwg.org/standards.html>.

   [PWG5100.14] McDonald, I. and M. Sweet, "PWG IPP Everywhere", PWG
                5100.14, January 2013,
                <http://www.pwg.org/standards.html>.

   [RFC2119]    Bradner, S., "Key words for use in RFCs to Indicate
                Requirement Levels", BCP 14, RFC 2119, March 1997,
                <http://www.rfc-editor.org/info/rfc2119>.

   [RFC2910]    Herriot, R., Ed., Butler, S., Moore, P., Turner, R., and
                J. Wenn, "Internet Printing Protocol/1.1: Encoding and
                Transport", RFC 2910, September 2000,
                <http://www.rfc-editor.org/info/rfc2910>.

   [RFC2911]    Hastings, T., Ed., Herriot, R., deBry, R., Isaacson, S.,
                and P. Powell, "Internet Printing Protocol/1.1: Model
                and Semantics", RFC 2911, September 2000,
                <http://www.rfc-editor.org/info/rfc2911>.






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   [RFC5246]    Dierks, T. and E. Rescorla, "The Transport Layer
                Security (TLS) Protocol Version 1.2", RFC 5246, August
                2008, <http://www.rfc-editor.org/info/rfc5246>.

   [RFC7230]    Fielding, R., Ed., and J. Reschke, Ed., "Hypertext
                Transfer Protocol (HTTP/1.1): Message Syntax and
                Routing", RFC 7230, June 2014,
                <http://www.rfc-editor.org/info/rfc7230>.

   [RFC7231]    Fielding, R., Ed., and J. Reschke, Ed., "Hypertext
                Transfer Protocol (HTTP/1.1): Semantics and Content",
                RFC 7231, June 2014,
                <http://www.rfc-editor.org/info/rfc7231>.

   [STD63]      Yergeau, F., "UTF-8, a transformation format of ISO
                10646", STD 63, RFC 3629, November 2003,
                <http://www.rfc-editor.org/info/sstd63>.

   [STD66]      Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
                Resource Identifier (URI): Generic Syntax", STD 66, RFC
                3986, January 2005,
                <http://www.rfc-editor.org/info/std66>.

   [STD68]      Crocker, D., Ed., and P. Overell, "Augmented BNF for
                Syntax Specifications: ABNF", STD 68, RFC 5234, January
                2008, <http://www.rfc-editor.org/info/std68>.

7.2.  Informative References

   [BCP35]      Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
                Registration Procedures for New URI Schemes", BCP 35,
                RFC 4395, February 2006,
                <http://www.rfc-editor.org/info/bcp35>.

   [CUPS]       Apple, "CUPS", Version 2.0.2, <https://www.cups.org/>.

   [IPPREG]     Internet Assigned Numbers Authority (IANA) Registries,
                "Internet Printing Protocol (IPP) Registrations",
                <http://www.iana.org/assignments/ipp-registrations/>.

   [PORTREG]    Internet Assigned Numbers Authority (IANA) Registries,
                "Service Name and Transport Protocol Port Number
                Registry",
                <http://www.iana.org/assignments/port-numbers>.

   [PWG5100.15] M. Sweet, "PWG IPP FaxOut Service", PWG 5100.15, June
                2014, <http://www.pwg.org/standards.html>.




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   [PWG5100.17] P. Zehler, "PWG IPP Scan Service", PWG 5100.17,
                September 2014, <http://www.pwg.org/standards.html>.

   [RFC793]     Postel, J., "Transmission Control Protocol", STD 7, RFC
                793, September 1981,
                <http://www.rfc-editor.org/info/rfc793>.

   [RFC1179]    McLaughlin, L., "Line printer daemon protocol", RFC
                1179, August 1990,
                <http://www.rfc-editor.org/info/rfc1179>.

   [RFC2566]    deBry, R., Hastings, T., Herriot, R., Isaacson, S., and
                P. Powell, "Internet Printing Protocol/1.0: Model and
                Semantics", RFC 2566, April 1999,
                <http://www.rfc-editor.org/info/rfc2566>.

   [RFC2569]    Herriot, R., Ed., Hastings, T., Jacobs, N., and J.
                Martin, "Mapping between LPD and IPP Protocols", RFC
                2569, April 1999,
                <http://www.rfc-editor.org/info/rfc2569>.

   [RFC2817]    Khare, R. and S. Lawrence, "Upgrading to TLS Within
                HTTP/1.1", RFC 2817, May 2000,
                <http://www.rfc-editor.org/info/rfc2817>.

   [RFC3196]    Hastings, T., Manros, C., Zehler, P., Kugler, C., and H.
                Holst, "Internet Printing Protocol/1.1: Implementor's
                Guide", RFC 3196, November 2001,
                <http://www.rfc-editor.org/info/rfc3196>.

   [RFC3510]    Herriot, R. and I. McDonald, "Internet Printing
                Protocol/1.1: IPP URL Scheme", RFC 3510, April 2003,
                <http://www.rfc-editor.org/info/rfc3510>.

   [RFC3712]    Fleming, P. and I. McDonald, "Lightweight Directory
                Access Protocol (LDAP): Schema for Printer Services",
                RFC 3712, February 2004,
                <http://www.rfc-editor.org/info/rfc3712>.

   [TLSBCP]     Scheffer, Y., Holz, R., and P. Saint-Andre,
                "Recommendations for Secure Use of TLS and DTLS", Work
                in Progress, draft-ietf-uta-tls-bcp, December 2014.









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Acknowledgments

   This document has been submitted to the IETF by the Internet Printing
   Protocol Working Group of the IEEE-ISTO Printer Working Group, as
   part of their PWG IPP Everywhere [PWG5100.14] project for secure
   mobile printing with vendor-neutral Client software.

   This document defines an alternate IPP transport binding to that
   defined in the original IPP URL Scheme [RFC3510], but this document
   does not update or obsolete [RFC3510].

   Thanks to Claudio Allochio, Jari Arrko, Spencer Dawkins, Adrian
   Farrel, Tom Hastings, Bjoern Hoerhmann, Smith Kennedy, Graham Klyne,
   Barry Leiba, S. Moonesamy, Kathleen Moriarty, Sandra Murphy, Tom
   Petch, Pete Resnick, Benson Schliesser, Robert Sparks, Jerry
   Thrasher, Mykyta Yevstifeyev, Pete Zehler, and the members of the
   IEEE-ISTO PWG IPP WG.

Authors' Addresses

   Ira McDonald
   High North, Inc.
   221 Ridge Ave
   Grand Marais, MI 49839
   United States

   Phone: +1 906-494-2434
   EMail: blueroofmusic@gmail.com


   Michael Sweet
   Apple, Inc.
   1 Infinite Loop, M/S 111-HOMC
   Cupertino, CA 95014
   United States

   EMail: msweet@apple.com














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