MIC calculation discrepancy?

Hello, I am hoping someone can help me... we are
testing some in-house software to do AS2
communications, and we have had problems connecting to
Walmart. We can send signed and encrypted messages
just fine and we receive a proper MDN; however we are
not able to verify the Message Integrity Check
returned in Walmart's MDN. In particular if we sign,
encrypt, and send the same test message repeatedly we
get a different value for the MIC each time!

I am a bit confused as to how this could be, as RFC
3335 and the AS2 spec indicate that the MIC should be
calculated over the original EDI data and MIME header.
Moreover we have not had this issue connecting with
other servers. Is this a known issue with Wal-Mart's
EDI solution? Or am I doing something wrong?

Thank you!

Best regards,

Michael Milner


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