RE: [wss] New Issue: Key Identifiers Should Not Be Used for Signatures

[Tim Moses <tim.moses@entrust.com>]

Merlin - CMS references certificates by issuer/serial.  One of the reasons
for this is that (as Hal points out) a key may be valid, but only for
certain purposes, as indicated by its certificate policy identifiers.  An
X.509 certificate does more than bind a name and a key independent of usage.
The CMS approach works provided CAs use a different serial number in every
certificate they issue.  We should follow their example.  All the best.
Tim.

-----Original Message-----
From: merlin [mailto:merlin@baltimore.ie]
Sent: Tuesday, June 17, 2003 11:47 AM
To: Hal Lockhart
Cc: wss@lists.oasis-open.org
Subject: Re: [wss] New Issue: Key Identifiers Should Not Be Used for
Signatures 


r/hlockhar@bea.com/2003.06.17/10:06:12
>The problem is that the Relying Party has know way of knowing how many
>certificates the sender has. At a minumum I would say this makes the spec
>totally useless for non-repudiation purposes and even doubtful for ordinary
>Authorization.

I think that this certificate substitution attack is no
different from the attack of submitting the initial request
with certificate B (same key) instead.

The recipient trusts certain CAs, presumably based upon
their security policies. If one of the CA/PKI systems asserts
that an identity/key binding is valid, the requestor proves
ownership of the key, and the identity is sufficient for the
recipient to authorize the request, then the request will
be processed. It is up to the recipient not to accept certs
issued by CAs that don't have adequate security policies.

Merlin


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