Subject: [Suit] COSE Digest in the manifest

From: Jim Schaad <[email-masked]>
Date: Mon, 12 Nov 2018 21:03:21 +0700

As Brendan mentioned during the F2F meeting I have already contacted him
about this issue.

When COSE was developed, it was a very deliberate decision that there would
be no digest structure as part of the specification.  For the most part when
people need a digest all that is needed is an array of two elements:  The
algorithm to use and the result of the digest.  In other cases what is
desired is three elements.  The same first two elements but also a URL or
some other pointer to the content which is being digested.

The digest structure itself has zero security properties in terms of
protecting a third party from modifying things.  Since there is no secret
value involved anybody can change the content, the digest and the algorithm
at will if there is not an additional layer of security that is applied. In
the case of the manifest, that additional security is applied by signing the
entire object including the ones noted above.

Not that this change will lead to drastically simpler processing of digested
content as there is no need to do the digest of the content and then digest
that result with some other things and finally compare that result against
the transmitted value.

Jim