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MD2(3)                   BSD Library Functions Manual                   MD2(3)

NAME
     MD2Init, MD2Update, MD2Final, MD2End, MD2File, MD2Data -- calculate the
     RSA Data Security, Inc., ``MD2'' message digest

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <&lt;sys/types.h>&gt;
     #include <&lt;md2.h>&gt;

     void
     MD2Init(MD2_CTX *context);

     void
     MD2Update(MD2_CTX *context, const unsigned char *data, unsigned int len);

     void
     MD2Final(unsigned char digest[16], MD2_CTX *context);

     char *
     MD2End(MD2_CTX *context, char *buf);

     char *
     MD2File(const char *filename, char *buf);

     char *
     MD2Data(const unsigned char *data, unsigned int len, char *buf);

DESCRIPTION
     The MD2 functions calculate a 128-bit cryptographic checksum (digest) for
     any number of input bytes.  A cryptographic checksum is a one-way hash-
     function, that is, you cannot find (except by exhaustive search) the
     input corresponding to a particular output.  This net result is a ``fin-
     gerprint'' of the input-data, which doesn't disclose the actual input.

     MD2 is the slowest, MD4 is the fastest and MD5 is somewhere in the mid-
     dle.  MD2 can only be used for Privacy-Enhanced Mail.  MD4 has been crit-
     icized for being too weak, so MD5 was developed in response as ``MD4 with
     safety-belts''.  When in doubt, use MD5.

     The MD2Init(), MD2Update(), and MD2Final() functions are the core func-
     tions.  Allocate an MD2_CTX, initialize it with MD2Init(), run over the
     data with MD2Update(), and finally extract the result using MD2Final().

     MD2End() is a wrapper for MD2Final() which converts the return value to a
     33-character (including the terminating '\0') ASCII string which repre-
     sents the 128 bits in hexadecimal.

     MD2File() calculates the digest of a file, and uses MD2End() to return
     the result.  If the file cannot be opened, a null pointer is returned.
     MD2Data() calculates the digest of a chunk of data in memory, and uses
     MD2End() to return the result.

     When using MD2End(), MD2File(), or MD2Data(), the buf argument can be a
     null pointer, in which case the returned string is allocated with
     malloc(3) and subsequently must be explicitly deallocated using free(3)
     after use.  If the buf argument is non-null it must point to at least 33
     characters of buffer space.

SEE ALSO
     md2(3), md4(3), md5(3)

     B. Kaliski, The MD2 Message-Digest Algorithm, RFC 1319.

     R. Rivest, The MD4 Message-Digest Algorithm, RFC 1186.

     R. Rivest, The MD5 Message-Digest Algorithm, RFC 1321.

     RSA Laboratories, Frequently Asked Questions About today's Cryptography.

HISTORY
     These functions appeared in NetBSD 1.3.

AUTHORS
     The original MD2 routines were developed by RSA Data Security, Inc., and
     published in the above references.  This code is derived directly from
     these implementations by Poul-Henning Kamp <phkATlogin.dk>

     Phk ristede runen.

BUGS
     No method is known to exist which finds two files having the same hash
     value, nor to find a file with a specific hash value.  There is on the
     other hand no guarantee that such a method doesn't exist.

COPYRIGHT
     This code is in the public domain.

BSD                              June 13, 2003                             BSD