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MD2(3)		       FreeBSD Library Functions Manual			MD2(3)

NAME
     MD2Init, MD2Update, MD2Pad, MD2Final, MD2End, MD2File, MD2FileChunk,
     MD2Data --	calculate the RSA Data Security, Inc., ``MD2'' message digest

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

SYNOPSIS
     #include <sys/types.h>
     #include <md2.h>

     void
     MD2Init(MD2_CTX *context);

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

     void
     MD2Pad(MD2_CTX *context);

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

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

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

     char *
     MD2FileChunk(const	char *filename,	char *buf, off_t offset,
	 off_t length);

     char *
     MD2Data(const void	*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
     ``fingerprint'' of	the input-data,	which does not 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 now	been
     broken; it	should only be used where necessary for	backward compatibil-
     ity.  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 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().

     The MD2Pad() function can be used to pad message data in same way as done
     by	MD2Final() without terminating calculation.

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

     The MD2File() function calculates the digest of a file, and uses MD2End()
     to	return the result.  If the file	cannot be opened, a null pointer is
     returned.	The MD2FileChunk() function is similar to MD2File(), 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, MD2FileChunk() calculates the digest	from offset to the end of
     file.  The	MD2Data() function 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), sha(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.

     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 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	<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.

     MD2 has only been licensed	for use	in Privacy Enhanced Mail.  Use MD4 or
     MD5 if that is not	what you are doing.  Copyright (C) 1990-2, RSA Data
     Security, Inc. Created 1990. All rights reserved.

     License to	copy and use this software is granted for non-commercial
     Internet Privacy-Enhanced Mail provided that it is	identified as the "RSA
     Data Security, Inc. MD2 Message Digest Algorithm" in all material men-
     tioning or	referencing this software or this function.

     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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