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MD5(3)		       FreeBSD Library Functions Manual			MD5(3)

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

LIBRARY
     Message Digest (MD4, MD5, etc.) Support Library (libmd, -lmd)

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

     void
     MD5Init(MD5_CTX *context);

     void
     MD5Update(MD5_CTX *context, const void *data, unsigned int	len);

     void
     MD5Pad(MD5_CTX *context);

     void
     MD5Final(unsigned char digest[16],	MD5_CTX	*context);

     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 void	*data, unsigned	int 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 does not disclose	the actual
     input.

     MD4 is the	fastest	and MD5	is somewhat slower.  MD4 has now been broken;
     it	should only be used where necessary for	backward compatibility.	 MD5
     has not yet (1999-02-11) been broken, but sufficient attacks have been
     made that its security is in some doubt.  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 pad message data in same way as done
     by	MD5Final() without terminating calculation.

     The MD5End() function is a	wrapper	for MD5Final() which converts the
     return value to a 33-character (including the terminating '\0') ASCII
     string which represents the 128 bits in hexadecimal.

     The MD5File() function calculates the digest of a file, and uses MD5End()
     to	return the result.  If the file	cannot be opened, a null pointer is
     returned.	The MD5FileChunk() function is similar to MD5File(), but it
     only calculates the digest	over a byte-range of the file specified,
     starting at offset	and spanning length bytes.  If the length parameter is
     specified as 0, or	more than the length of	the remaining part of the
     file, MD5FileChunk() calculates the digest	from offset to the end of
     file.  The	MD5Data() function calculates the digest of a chunk of data in
     memory, and uses MD5End() to return the result.

     When using	MD5End(), MD5File(), 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 33
     characters	of buffer space.

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

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

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

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

     MJ. B. Robshaw, "On Recent	Results	for MD2, MD4 and MD5", RSA
     Laboratories Bulletin, 4, November	12, 1996.

HISTORY
     These functions appeared in FreeBSD 2.0.

AUTHORS
     The original MD5 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	<phk@FreeBSD.org>

     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	does not exist.	 Copyright (C)
     1991-2, RSA Data Security,	Inc. Created 1991. All rights reserved.

     License to	copy and use this software is granted provided that it is
     identified	as the "RSA Data Security, Inc.	MD5 Message-Digest Algorithm"
     in	all material mentioning	or referencing this software or	this function.

     License is	also granted to	make and use derivative	works provided that
     such works	are identified as "derived from	the RSA	Data Security, Inc.
     MD5 Message-Digest	Algorithm" in all material mentioning or referencing
     the derived work.

     RSA Data Security,	Inc. makes no representations concerning either	the
     merchantability of	this software or the suitability of this software for
     any particular purpose. It	is provided "as	is" without express or implied
     warranty of any kind.

     These notices must	be retained in any copies of any part of this documen-
     tation and/or software.

FreeBSD	9.2		       February	11, 1999		   FreeBSD 9.2

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | SEE ALSO | HISTORY | AUTHORS | BUGS

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