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Re: [smime] Problems with versions

2022-05-05 08:06:19

I wonder how many implementations defer the decoding of SignerInfos until after 
the version number is read. Mine does not, so presence of new SignerInfo or 
ReceipientInfo types would cause failure to parse without ever seeing the 
version number. I don't check the version number at all for 
SignedData/SignerInfo at verification time and just use whichever of SKID or 
issuer/serial is present. I have also never seen a v4 or v5. There aren't any 
extensibility markers in the places you’d need them to introduce new SignerInfo 
or ReceipientInfo types without breaking folks.

On 5/5/22, 8:34 AM, "smime on behalf of Peter Gutmann" 
<smime-bounces(_at_)ietf(_dot_)org on behalf of 
pgut001(_at_)cs(_dot_)auckland(_dot_)ac(_dot_)nz> wrote:

    Russ Housley <housley(_at_)vigilsec(_dot_)com> writes:

    >That is, an unrecognized version can save the recipient for getting a 

    But they won't be getting a parsing error, see the example I gave:

    >  SignedData {
    >    version = 7,
    >    digestAlgorithms,
    >    content,
    >    signerInfos {
    >      signerInfo version = 7,
    >      signerInfo version = 6,
    >      signerInfo version = 1
    >      }
    >    }

    If you change the SignedData version to 1 then an implementation that 
    understand version 6 or 7 signerInfos can still process the message because
    there's a version 1 signerInfo present.  However if you set it at 7 then the
    implementation is being told it can't (or shouldn't) process the message 
    though it can.

    The fact that there's some not-currently-recognised but totally processable
    (meaning read the header and skip the remaining payload) entry somewhere
    further down in the message doesn't mean that the whole message should be
    marked as unprocessable by an implementation.

    If there's any implementers still on the list, what would your code do if it
    encountered the above message?  And what would it do if the SignedData 
    was 1 instead of 7?


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