RE: Problem verifying a signed message

Manfred:

Thank you for your detailed analysis, I was able to diagnose the
encoding more quickly.

After investigating our ASN.1 encoding of the signed attributes of this
message, I believe the SFL encoding is correct.  The encoding difference
is due to the ASN.1 DER encoding rule that states that the SEQUENCE OF
must be numerically ordered.  The SFL ordering is correct, but in this
case it may not be obvious why.  The DER rules indicate the the ordering
must be made on the data, not the outer tag and length.  Ignoring the
tag and length, the 2nd and 3rd SEQUENCE items of the SignedAttrs are as
follows (from original message not re-encoded results):

...
30 18 06 09 2A 86 48 86 F7 OD 01 09 03 31 0B 06 ...
30 1C 06 09 2A 86 48 86 F7 OD 01 09 05 31 0F 17 ...
30 23 06 09 2A 86 48 86 F7 OD 01 09 04 31 16 04 ...
...

Our DER re-encoded results:
...
30 18 06 09 2A 86 48 86 F7 OD 01 09 03 31 0B 06 ...
30 23 06 09 2A 86 48 86 F7 OD 01 09 04 31 16 04 ...
30 1C 06 09 2A 86 48 86 F7 OD 01 09 05 31 0F 17 ...
                                    ** <<< ORDERED VALUE >>>
...

IGNORING the 23 AND 1C lengths, the ordering occurs on the "**" flagged
values (04 AND 05).

I hope this helps.  I personally wrote this particular DER encoding
modification in the SNACC compiler (it was originally a BER encoding
compiler).  You may already be aware of this, but if you attempt to
write the logic that sorts the SEQUENCE OF elements, be careful of the
byte count of the lengths (82 01 01 for example indicates 2 bytes, 257
value).

Bob Colestock
VDA.

-----Original Message-----
From: [email protected] [mailto:[email protected]]
Sent: Monday, March 18, 2002 8:40 AM
To: [email protected]
Subject: Problem verifying a signed message


I have a problem during signature verification of the attached message.

In the function "CSM_MsgSignerInfo::Verify", the authenticatedAttributes
are encoded via snacc and then
SMTI_Verify is called for signatur verification.

The problem is that snacc produces an different order for the attributes
than the original signer of
the message, so the verification fails.

The question now is, which encoding is correct?

I have observed the same problem with messages signed by Mozilla 0.9.8.

Any help would be greatly appreciated.

Thanks,

Manfred Klug


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