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Re: New text for X.501


David,

David Chadwick wrote: 
Dear LDAPers

At the recent Geneva meeting of the X.500 group, Defect Report 303 was
discussed. This concerns the fact that a user cannot be guaranteed that
the information presented to LDAP/X.500 server in an update operation is
subsequently returned unaltered in a Search operation. Due to this, in
the PKIX work we are adding text to the IDs specifically to say that for
X.509 certificates and CRLs the data must not be altered by the LDAP
server. The X.500 group is going to go one step further than this and
state that no attributes must be altered by the server and must be
returned exactly as presented,


I think this change is ill-advised, as the requirement cannot be enforced
in a mixed LDAP/X.500 distributed environment. An attribute value that is
entered in an LDAP-specific encoding has to be transformed into BER to be
carried in DSP or DISP. There is no guarantee that the exact LDAP-specific
encoding of the original attribute value will be reconstructed by the
receiving DSA. Preservation of the exact encoding of PKI attributes can
only be made to work in the general case because the LDAP encoding and the
X.500 encoding is the same - BER. For most syntaxes this is not the case.

The XED specifications introduce a third way of encoding directory data (DXER),
which only increases the difficulty of preserving the original encoding.

If the X.500 standards add this requirement then, as a practical necessity,
I will have to disregard it. However, I will continue to preserve the abstract
value of attribute values to the extent that it is possible to do so.

Regards,
Steven

although a server may store a
canonicalised form for efficient matching if it so desires.

The defect report can only address the 1997 and 2001 versions of X.500,
since the 1993 version that LDAP is based in is no longer supported by
ITU-T/ISO.

Here is the gist of the proposed text to fix the defect report.

Stored attribute values must be held as supplied. We propose to add text
to X.501 in clause 8.5 and in 8.8.1, where we will point out that
rationalizations to stored values for the purposes of matching do not
effect the stored value. We will also add text to clause 6.1 of x.520
stating that the rationalizations describe in the matching rules are
ephemeral, for the purpose of the match only, and will not affect the
stored value.

Regards

David