Re: Message takeover attacks against S/MIME

Peter:

> 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.

CMS already supports Enveloped-Data and Authenticated-Enveloped-Data.  However, the S/MIME specification does not say how to use Authenticated-Enveloped-Data.  I think that is the work to be done.

Russ

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