ietf-smime
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Re: Countersignature within CMS

1998-07-02 04:10:59
At 08:35 30/06/98 -0700, you wrote:
At 09:41 AM 6/30/98 +0100, William Ottaway wrote:
I could propose a paragraph but I would like to hold off for a while. We
will be releasing an internet draft on domain security services using
S/MIME within the next couple of weeks and I want to take on board the
comments it will raise before addressing the Countersignature issue.

Well, I would rather not delay the S/MIME work, so I'll propose one. Anyone
should feel free to comment on this.

A countersignature can be created without the countersigner knowing the
original content. The recipient who is validating the countersignature has
no way of knowing if the signature that was countersigned is valid without
checking that signature as well. Thus, a recipient who can validate a
countersignature but cannot validate the original signature must not infer
that the content that was signed has not been modified, and must not infer
that the original signer actually had access to the content.

--Paul Hoffman, Director
--Internet Mail Consortium

Paul,

Thankyou for your contribution to this thread.

Shouldn't the last sentence read "..., and must not infer that the counter
signer actually had access to the content."? Or, are you thinking about a
scenario where a counter signature is bound to another counter signature?

If the former then your text is acceptable in that it clearly states to the
reader the implications of using a counter signature. If the latter then I
don't accept the proposed text because the last sentence is confusing.

I still question the usefulness of a counter signature. If a counter
signature is used then the recipient must be able to verify the originators
signature. In the less than ideal world I see there being disjoint PKIs
where it would be very common for a recipient not to be able to verify the
originators signature, but may be able to verify a counter signing
signature. If the recipient knew that the counter signer had already
verified the signature it is signing then the recipient would be in a
position to accept the message. 

I hope that this scenario will be resolved in a manner acceptable to this
working group within our internet draft on domain security services using
S/MIME, to be released shortly.

For the time being I am willing to accept the additional paragraph, as long
as the last sentence is changed as stated above. But there may be some
repercussions when our draft is released.

Bill.  
_____________________________________________________________________
William Ottaway,             Tel: +44 (0)1684 894079
DERA Malvern,                Fax: +44 (0)1684 896113
St. Andrews Road,            email: 
w(_dot_)ottaway(_at_)eris(_dot_)dera(_dot_)gov(_dot_)uk
Malvern,
Worcs, WR14 3PS
UK


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