Subject: Re: I-D ACTION:draft-ietf-ldapbis-protocol-06.txt

From: David Chadwick <[email-masked]>
Date: Sun, 24 Feb 2002 23:17:39 +0000

Jim

I think the new text for attribute descriptions is very good. Much
better than before, especially the description of subtyping. However,
the subsection on Binary Option (4.1.5.1) could still do with some
improvement I feel. Firstly, the section is not as clear as recent email
we have had on the list, explaining that the attribute value, whatever
it is, is treated (or turned into) as an octet string containing BER,
and then a TL octet wrapper is placed around it. 

Secondly, the section talks about overriding the native encoding and
sending it as BER instead. But then your example uses certificates, that
are native BER encoded. So what overriding is there to take place. It
would seem like none, and therefore the effect of ;binary is null. In
other words the section does not clearly indicate to me what the
difference would be in transferring a certificate without ;binary and
one with i.e. certificate;binary.  This is unfortunate and confusing to
the reader. I suggest you use an example that is not a certificate, but
is a simple string. You might then also add text to say what the effect
of ;binary is on a value that is already BER encoded.

I find this sentence particular confusing

"Instead the attribute is to be transferred as 
   a binary value encoded using the Basic Encoding Rules [X.690]."

The reason it is confusing is that all values in BER are binary. So if
the value is already BER what more needs to be done to it? It would seem
nothing.

Perhaps the sentence might read better as

"Instead the attribute value is transferred as an ASN.1 OctetStringType,
where the embedded octet string value is itself a BER encoded value" 

The second sentence
"The 
   syntax of the binary value is an ASN.1 data type definition, which is 
   referenced by the "SYNTAX" part of the attribute type definition."

also has some errors in it, and could then be changed to

"The syntax of the BER encoded value is an ASN.1 data type, which 
must conform to the "SYNTAX" part of the AttributeTypeDescription."

Is that any better?

David

Jim Sermersheim wrote:
> 
> All,
> 
> This revision contains the changes recommended by the attribute options
> engineering team. Please review section 4.1.5 carefully.
> 
> Other changes are listed in section B.7
> 
> Jim
> 
> >>> <[email-masked]> 01/31/02 05:00AM >>>
> A New Internet-Draft is available from the on-line Internet-Drafts
> directories.
> This draft is a work item of the LDAP (v3) Revision Working Group of
> the IETF.
> 
>         Title           : Lightweight Directory Access Protocol (v3)
>         Author(s)       : J. Sermersheim
>         Filename        : draft-ietf-ldapbis-protocol-06.txt
>         Pages           : 56
>         Date            : 30-Jan-02
> 
> The protocol described in this document is designed to provide access
> to directories supporting the [X.500] models, while not incurring the
> resource requirements of the X.500 Directory Access Protocol (DAP).
> This protocol is specifically targeted at management applications and
> browser applications that provide read/write interactive access to
> directories. When used with a directory supporting the X.500
> protocols, it is intended to be a complement to the X.500 DAP.
> 
> A URL for this Internet-Draft is:
> http://www.ietf.org/internet-drafts/draft-ietf-ldapbis-protocol-06.txt
> 
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-- 
*****************************************************************

David W. Chadwick, BSc PhD
Professor of Information Systems Security
IS Institute, University of Salford, Salford M5 4WT
Tel: +44 161 295 5351  Fax +44 161 745 8169
Mobile: +44 77 96 44 7184
Email: [email-masked]
Home Page:  http://www.salford.ac.uk/its024/chadwick.htm
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---

From: "Steven Legg" <[email-masked]>
Date: Mon, 25 Feb 2002 12:22:52 +1100

David,

> and then a TL octet wrapper is placed around it.

This is not the interpretation Kurt and I have been describing. An
AttributeValue in LDAP is an OCTET STRING. The contents octets of this
OCTET STRING are either a series of UTF8 encoded characters (being a
human-readable native LDAP encoding), a series of arbitrary octets
(being the native LDAP encoding for, e.g., the Octet String syntax -
1.3.6.1.4.1.1466.115.121.1.40) or a BER encoded value (comforming to
the ASN.1 type corresponding to the LDAP syntax).
There is no extra OCTET STRING wrapper around the BER encoding.

By way of example, the contents octets of AttributeValue for the value
"foo" returned as a value of cn would be (in hexadecimal): 66 6F 6F .

Returned as a value of cn;binary it would be: 13 03 66 6F 6F,
the BER for a value of the printableString alternative from the
DirectoryString{} CHOICE. No OCTET STRING tags to be seen.

> are native BER encoded.

The Certificate syntax does not have a native encoding in LDAPv3.

> So what overriding is there to take place. It
> would seem like none, and therefore the effect of ;binary is null.

"Overriding" is perhaps the wrong way to describe it, since for some
syntaxes there is no native LDAP encoding to override. I prefer to think
of binary as an *alternative* way of encoding a value. For some syntaxes,
like Certificate, there is no choice because there is only one alternative
defined.

> In
> one with i.e. certificate;binary.

The difference is that "certificate" without ";binary" is illegal.
The native LDAP encoding is, at present, undefined.

> This is unfortunate and
> confusing to

RFC 2252 allows a server to store a value in any format it likes.
If a value is stored as BER then it can be returned in ";binary"
form without conversion. If stored in the native LDAP encoding
then to be returned in ";binary" form it must first be re-encoded
(as BER). The converse applies if the value is requested in native
LDAP form.

> where the embedded octet string value is itself a BER encoded value"

No, this suggests an extra OCTET STRING wrapper.

> must conform to the "SYNTAX" part of the AttributeTypeDescription."

I would prefer:

"The value is BER encoded according to the ASN.1 data type
corresponding to the attribute's LDAP syntax. The LDAP syntax is
indicated by the "SYNTAX" part of the AttributeTypeDescription."

... with corresponding ASN.1 types nominated for each syntax in RFC 2252bis.

Regards,
Steven