References

   [1] Rivest, R., "The MD4 Message Digest Algorithm", RFC 1320, MIT and
       RSA Data Security, Inc., April 1992.

   [2] Rivest, R., "The MD4 message digest algorithm", in A.J.  Menezes
       and S.A. Vanstone, editors, Advances in Cryptology - CRYPTO '90
       Proceedings, pages 303-311, Springer-Verlag, 1991.

   [3] CCITT Recommendation X.509 (1988), "The Directory -
       Authentication Framework."