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Re: [smime] Problems with versions

2022-05-05 09:45:49

The first versions of PKCS#7 and then CMS (RFC2630) all used the earlier 
version of ASN.1, so extensibility markers did not exist yet.  So, the version 
number logic gives the recipient a heads up about the fields that might be 

RFC 5911 uses the new ASN.1 syntax, and it makes use extension markers.  It 
also makes use of the ASN.1 idiom for noting in which version of CMS changes 
were made from the original PKCS #7.  For example:

   RevocationInfoChoice ::= CHOICE {
       crl CertificateList,
       [[5: other [1] IMPLICIT OtherRevocationInfoFormat ]] }


On May 5, 2022, at 9:06 AM, Carl Wallace 
<carl(_at_)redhoundsoftware(_dot_)com> wrote:


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 parsing

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

SignedData {
  version = 7,
  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 
   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 
   encountered the above message?  And what would it do if the SignedData 
   was 1 instead of 7?


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