MD5(3bsd)			     LOCAL			     MD5(3bsd)

NAME
     MD5Init, MD5Update, MD5Pad, MD5Final, MD5Transform, MD5End, MD5File,
     MD5FileChunk, MD5Data — calculate the RSA Data Security, Inc., ``MD5''
     message digest

LIBRARY
     Utility functions from BSD systems (libbsd, -lbsd)

SYNOPSIS
     #include <sys/types.h>
     #include <bsd/md5.h>

     void
     MD5Init(MD5_CTX *context);

     void
     MD5Update(MD5_CTX *context, const u_int8_t *data, size_t len);

     void
     MD5Pad(MD5_CTX *context);

     void
     MD5Final(u_int8_t digest[MD5_DIGEST_LENGTH], MD5_CTX *context);

     void
     MD5Transform(u_int32_t state[4], u_int8_t block[MD5_BLOCK_LENGTH]);

     char *
     MD5End(MD5_CTX *context, char *buf);

     char *
     MD5File(const char *filename, char *buf);

     char *
     MD5FileChunk(const char *filename, char *buf, off_t offset,
	 off_t length);

     char *
     MD5Data(const u_int8_t *data, size_t len, char *buf);

DESCRIPTION
     The MD5 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
     “fingerprint” of the input-data, which doesn't disclose the actual input.

     MD4 has been broken; it should only be used where necessary for backward
     compatibility.  MD5 has not yet (1999-02-11) been broken, but recent
     attacks have cast some doubt on its security properties.  The attacks on
     both MD4 and MD5 are both in the nature of finding “collisions” - that
     is, multiple inputs which hash to the same value; it is still unlikely
     for an attacker to be able to determine the exact original input given a
     hash value.

     The MD5Init(), MD5Update(), and MD5Final() functions are the core func‐
     tions.  Allocate an MD5_CTX, initialize it with MD5Init(), run over the
     data with MD5Update(), and finally extract the result using MD5Final().

     The MD5Pad() function can be used to apply padding to the message digest
     as in MD5Final(), but the current context can still be used with
     MD5Update().

     The MD5Transform() function is used by MD5Update() to hash 512-bit blocks
     and forms the core of the algorithm.  Most programs should use the inter‐
     face provided by MD5Init(), MD5Update() and MD5Final() instead of calling
     MD5Transform() directly.

     MD5End() is a wrapper for MD5Final() which converts the return value to
     an MD5_DIGEST_STRING_LENGTH-character (including the terminating '\0')
     ASCII string which represents the 128 bits in hexadecimal.

     MD5File() calculates the digest of a file, and uses MD5End() to return
     the result.  If the file cannot be opened, a null pointer is returned.

     MD5FileChunk() behaves like MD5File() but calculates the digest only for
     that portion of the file starting at offset and continuing for length
     bytes or until end of file is reached, whichever comes first.  A zero
     length can be specified to read until end of file.	 A negative length or
     offset will be ignored.  MD5Data() calculates the digest of a chunk of
     data in memory, and uses MD5End() to return the result.

     When using MD5End(), MD5File(), MD5FileChunk(), or MD5Data(), 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 MD5_DIGEST_STRING_LENGTH characters of buffer space.

SEE ALSO
     cksum(1), md5(1), adler32(3), md4(3), rmd160(3), sfv(3), sha1(3),
     sha2(3), suma(3), tiger(3), whirlpool(3)

     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,
     <http://www.rsa.com/rsalabs/faq/>.

     H. Dobbertin, "Alf Swindles Ann", CryptoBytes, 1(3):5, 1995.

     MJ. B. Robshaw, "On Recent Results for MD4 and MD5", RSA Laboratories
     Bulletin, 4, November 12, 1996.

     Hans Dobbertin, Cryptanalysis of MD5 Compress.

HISTORY
     These functions appeared in OpenBSD 2.0.

AUTHORS
     The original MD5 routines were developed by RSA Data Security, Inc., and
     published in the above references.	 This code is derived from a public
     domain implementation written by Colin Plumb.

     The MD5End(), MD5File(), MD5FileChunk(), and MD5Data() helper functions
     are derived from code written by Poul-Henning Kamp.

BUGS
     Collisions have been found for the full versions of both MD4 and MD5 as
     well as strong attacks against the SHA-0 and SHA-1 family.	 The use of
     sha2(3), or rmd160(3) is recommended instead.

BSD				April 29, 2004				   BSD

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