Signing encrypted data & PKCS7/CMS thoughts

Ed writes:
> The wonderful thing about XML Signature and XML Encryption is that it is
very flexible in ways that simply were not possible with CMS and PKCS7.  
 
Although I agree with this in spirit, it's also our biggest problem in my
opinion. To the extent that we enable app developers to
reuse keys, combine signature/encryption, etc, we run risks of creating
footholds for cryptanalysis that
aren't present in PKCS7/CMS.  Publishing a spec that puts the burden of
cryptanalytic soundness on the app developer is
a useless, probably even dangerous activity.  
 
Suppose I believe that CMS and PKCS7 have a sound treatment of signing and
encryption from a 
cryptanalytic point of view.  It would be great if I knew that any
cryptanalytic attack on my 
XML Encryption/XML SIgnature application would lift to a PKCS 7 attack, ie,
that my XML app
is at least as secure as PKCS7.  Maybe there could be PKCS7 "profile" or
something?  
 
Whether this is possible or even a reasonable way to think of this I don't
know.  
 
Thane Plambeck
VeriSign