 a simple modification to HMAC-SHA-1 code to get
   HMAC-MD5 code, as explained in the Appendix.
<p>
   The test cases in this document are cross-verified by three
   independent implementations, one from NIST and two from IBM Research.
   One IBM implementation uses optimized code that is very different
   from the code in the Appendix. An implemenation that concurs with the
   results provided in this document should be interoperable with other
   similar implemenations.  We do not claim that such an impl