Re: [ldapext] [Fwd: New Version Notification for draft-pluta-ldap-srv-side-current-time-match-00]

[Steven Legg <[e-mail]>]

Hi Daniel,

Daniel Pluta wrote:
> Dear ldapext,
> 
> we would appreciate your valuable comments and feedback regrading our 
> draft specifying "ldap server side current time matching".

The draft is essentially about enforcing access control policy through
schema mechanisms, which strikes me as inappropriate for two principal
reasons:

(1) Schema is supposed to be immutable, whereas access control policy
is subject to change. If access control policy is reflected in the
attribute syntaxes one chooses, then that policy is permanently locked-in.

(2) Schema is one-size-fits-all. The same rules apply to everyone,
regardless of whether they are anonymous guest users or highly privileged
administrators. Access control policy is rarely that uniform.

Privacy goals should be addressed through access control mechanisms,
but of course you are hampered by the absence of a common, standardized
access control mechanism across all LDAP implementations. With that in
mind I would take a somewhat different approach to a solution.

Basically you want to allow general access to a derived property of
a collection of attributes while simultaneously enforcing restricted
access to that collection of attributes. What I would do is define a
schema mechanism for defining derived attributes, i.e., attributes
whose values are algorithmically derived by the server from the values
of other attributes in the same entry. The derived attributes can then
be subject to different access controls than the source attributes.

In your example with the notValidBefore and notValidAfter attributes,
I imagine having a derived attribute called currentlyValid, with
Boolean Syntax, that is derived from notValidBefore and
notValidAfter according to the following pseudo code:

     if (current time >= notValidBefore and
         current time <= notValidAfter) then
         value = TRUE
     else
         value = FALSE

Privileged users and processes would be given permission to read
and update the notValidBefore and notValidAfter attributes, but
regular users would only be able to read the currentlyValid
attribute. This kind of access control policy can be expressed in
existing LDAP access control schemes even though they differ between
implementations.

That takes care of the nowBefore and nowAfter syntaxes. I don't see
that you achieve anything with the nowBeforeOffset and nowAfterOffset
syntaxes since a user can just use a binary search to determine the
actual values of the target attributes by adjusting the offsets (a
client can guess the time at the server with reasonable accuracy).
Limiting the sign or magnitude of the offset would provide partial
protection, but a derived attribute could also do that. For example,
to allow regular users to determine when a valid account became valid
but not allow them to determine whether or when an account will become
valid at some time in the future I would define a derived attribute
of GeneralizedTime syntax whose values are determined by the following
pseudo code:

     if (current time >= notValidBefore)
         value = notValidBefore
     else
         absent

It becomes a question of how expressive should the derivation rules be
and what form should they take ? I think OpenLDAP might have some
capabilities in that area already.

The nowOffset syntax isn't required if derived attributes are used instead,
but if you want to persist with it I suggest you align it with the existing
ASN.1 DURATION data type (see http://www.itu.int/rec/T-REC-X.680-200606-S!Amd3/en )
rather than rolling your own format, not the least because I already have an
implementation that supports DURATION as an attribute and assertion syntax
for both X.500 and LDAP.

Regards,
Steven

> 
> Please see below for the abstract.
> 
> The full version can be found here: 
> http://www.ietf.org/id/draft-pluta-ldap-srv-side-current-time-match-00.txt
> 
> Many thanks in advance!
> 
> Best regards
> Daniel
> 
> 
> -------- Original-Nachricht --------
> Betreff: New Version Notification for 
> draft-pluta-ldap-srv-side-current-time-match-00
> Datum: Thu, 25 Mar 2010 15:51:33 -0700 (PDT)
> Von: IETF I-D Submission Tool <[e-mail]>
> 
> 
> A new version of I-D, 
> draft-pluta-ldap-srv-side-current-time-match-00.txt has been 
> successfully submitted and posted to the IETF repository.
> 
> Filename:     draft-pluta-ldap-srv-side-current-time-match
> Revision:     00
> Title:         Lightweight Directory Access Protocol (LDAP): Server Side 
> Current Time Matching - Matching Rules and Syntaxes
> Creation_date:     2010-03-25
> WG ID:         Independent Submission
> Number_of_pages: 20
> 
> Abstract:
> This document extends the Lightweight Directory Access Protocol
> (LDAP) to support server side current time matching.  Matching of
> attribute values against an LDAP server's current time offers
> additional functionality with regard to authorization and fulfills
> enhanced data privacy requirements for restrictive environments.
> Therefore this specification defines four additional syntaxes and
> related matching rules useful for extensible matching in association
> with these syntaxes.  In addition and for general use the matching
> rules defined in this document are also applicable to any attribute
> type definitions that are using the 'Generalized Time' syntax.  This
> specification also contains restrictive attribute type definitions
> demonstrating the usage of the introduced syntaxes and matching
> rules.
> 
> 
> 
> 
> The IETF Secretariat.
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