In relation to the proposed certificate, procedures for trust evaluation,
and authentication framework specified in ANSI X9.xx-1994, I would
ask two questions:-
(a) given that chain processing controls have been specified, along
with procedures, to allow wholly automated validation of the meaning
of CA certificates, what security service is provided when a digital
signature mechanism on such a CA certificate is positively validated?
(b) given that confidence in data origin authentication service provided
to a certificate user, upon validating a digital signature attached
to a end-entity certificate, may be a subjective measure by that user of
Subject Attributes, can an end-entity certificate userAuthentication key be used
to support a non-repudiation of origin security service for messages, as
defined in the X.400 Security Model?
I would comment that greater explanation of the semantics of UserKeyUsage
is required, explaining the role and general procedures assumed for
userAuthentication
and nonRepudiation Key Usages. I would comment that a differentiation is
required
between authenticating the origin of a key (set), and proving (possibly) with
non-repudiation, the origin of a message or other protocol element through
the use of that key in authentication or secure messaging procedures.
I would comment finally, that the authentication framework introduced by
this ANSI draft might not be compatible with PEM in a fundamental respect:
for PEM, the compatibility with X.509 1988 is assured, whilst also
binding the communication semantics of all digital signatures used in the
PEM system to provide for non-repudiation of origin security service for
the protected element of service.
Open discussion is welcome.
Peter.