Re: Message takeover attacks against S/MIME

Russ Housley <[email protected]> writes:

>Take a look at this article: http://cryptosource.de/posts/smime_mta_en.html
>
>Is there interest in updating the S/MIME specification to use authenticated-
>encryption?

It looks like a pretty contrived attack, you need to be able to truncate a
message, both at the start and end, on a 16-byte boundary to turn a signed
message into a plain, unsigned one, and still have the client accept the
result as a valid message.  They found one client that does that, but that
sounds more like a buggy client than a major problem (none of the others did
it).

In any case the fix should be pretty minimal, if anything is required at all:
If the SMIMECaps in the cert you're encrypting for indicates authEnc, use
that.  My code already does that and possibly other impementations do too.

Peter.
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