Subject: [AAA-WG]: [issue] Signed DSA messages

From: Miguel Ángel Monjas Llorente <[email-masked]>
Date: Wed, 22 Aug 2001 19:08:55 +0200

Submitter name: Miguel A. Monjas
Submitter email address: [email-masked] 
Date first submitted: 2001-08-22
Reference: 
Document: CMS-02
Comment type: T
Priority: 1
Section: 
Rationale/Explanation of issue: 

In some points of the specification, is stated that a DSA message
must/may be signed:

In 1.2:

   The DSAA MUST be signed by the proxy agent, and include its
   certificate, to allow the access device to validate the originator
   of the DSAA.

In 1.3:

   The CMS specification allows for Diameter AVPs to be
   multiply-signed

In 3.1

   - the DSAA message MUST be digitally signed and the signature
     MUST be validated and the signer's certificate chain MUST
     terminate as a CA mentioned in the DSAR message

and also

   The DSAR MAY be signed. If the originating node has a private key
   and protection expectations for AVPs are specified, then the DSAR
   SHOULD be signed.

   The DSAA MUST be signed by a Diameter agent or server within the
   user's realm, to prevent an intermediate node from modifying the
   protection expectations for AVPs.

Pat has agreed on changing that expression and saying that "...
(MAY|MUST) include the CMS-Signed-Data AVP".

However, I'm a little bit concerned when the presence of a
CMS-Signed-Data AVP is required. This AVP contains a digital signature
on other (or others) AVPs. Those protected AVPs must have the 'P' bit
set. But let's imagine that neither of the AVPs included in the
message have the 'P' bit set (maybe because the implementation does
not consider that they must be protected). I assume that the
implementation must detect those cases and, when a CMS-Signed-Data AVP
is required, set the 'P' bit of an AVP, maybe chosen randomly or maybe
fixed in the configuration (for example, the DSA-TTL AVP is always
present, so that the implementation might be configured to protect it
always when a digital signature is required). Is this issue up to the
implementation or should be specified in the specification?

Requested change: 

Add clarifying text

Regards

  // M.A.

-- 
  Miguel Angel Monjas Llorente
  Systems Engineer, GSM/UMTS Systems Management
  Ericsson España, S.A. (EEM) UMTS/GSM Databases
  Tel: +34 91 3393605                 Mob: +34 629 570196
  <mailto:[email-masked]>  Fax: +34 91 3392538
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