Subject: RE: AS2-SMIME : has the certificate to be included inside the signature?

From: "Dale Moberg" <[email-masked]>
Date: Thu, 5 Jun 2003 08:29:06 -0700

PKCS7/CMS always has a the issuer serial number to identify and retrieve
a certificate (from a local store or whatever) so that it is not
essential to include a certificate or certificate chain. 
 
While it is normal to check or verify signer certificate validity with
respect to a site's trusted roots no matter how a certificate is
retrieved (so including or not including a certificate is not a security
gap), two considerations point to opposite conclusions on including the
certificate/certificate chain. First, saving bandwidth favors omitting
the certificate and chain.  Second, having the certificates in the
message may for some implementations speed up some message processing
operations. 
 
An application should be able to deal with either case. 
 RFC 2633 is the operative RFC that is cited in AS2 and should also be
consulted.
 See for example section 3.7 which says:
 
  A sending agent that signs messages MUST have a certificate for the
   signature so that a receiving agent can verify the signature. There
   are many ways of getting certificates, such as through an exchange
   with a certificate authority, through a hardware token or diskette,
   and so on.
 
   S/MIME v2 [SMIMEV2] specified a method for "registering" public keys
   with certificate authorities using an application/pkcs10 body part.
   The IETF's PKIX Working Group is preparing another method for
   requesting certificates; however, that work was not finished at the
   time of this memo. S/MIME v3 does not specify how to request a
 
   certificate, but instead mandates that every sending agent already
   has a certificate. Standardization of certificate management is being
   pursued separately in the IETF.
 
And between 1999,  when that was published, and now, the situation
remains about the same on PKI setup, alignment, and maintenance.

So, if you are an implementer, do not depend on receiving a cert chain
in the message whose signature you will be checking.
As far as sending certificates, implementers might be well advised to be
able to configure their software to either include or omit.
The choice of a default behavior is not specified in AS2. But the motto
"Be conservative in what you send, liberal in what you can receive"
probably favors including the cert chain, and then allowing an
optimization to omit for bandwidth conservation where it is not
necessary.

	-----Original Message-----
	From: [email-masked]
[mailto:[email-masked]] 
	Sent: Thursday, June 05, 2003 6:58 AM
	To: [email-masked]
	Subject: AS2-SMIME : has the certificate to be included inside
the signature?

	Hello,

	I am new on this list - and I need your help.

	AS2: when sending a signed message (the original message which
can also be signed, or a signed MDN), has the signer's certificate to be
included inside of the signature MIME part?

	Is it mandatory or should AS2 compliant products accept both?
(signed messages containing the cert, or not containing it, in which
case they would try to find a certificate on the local key store etc.) 

	Regards,

	-----------------------------------------
	Ludan STOECKLE
	DSI Groupe Casino - Etudes

	04 77 45 48 01

	[email-masked] <mailto:[email-masked]> 
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