Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages


home | help
MD5(3)		       FreeBSD Library Functions Manual			MD5(3)

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

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

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

     MD5Init(MD5_CTX *context);

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

     MD5Pad(MD5_CTX *context);

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

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

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

     char *
     MD5Data(const unsigned char *data,	unsigned int len, char *buf);

     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 ``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 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

     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().

     MD5Pad() can be used to pad message data in same way as done by
     MD5Final()	without	terminating calculation.

     MD5End() is a wrapper for MD5Final() which	converts the return value to a
     33-character (including the terminating '\0') ASCII string	which repre-
     sents 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.
     MD5Data() 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.

     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.

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

     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.

     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 ristede runen.

     These functions appeared in FreeBSD 2.0.

     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.

     MD2 has only been licensed	for use	in Privacy Enhanced Mail.  Use MD4 or
     MD5 if that isn't what you're doing.  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	11.1		       February	11, 1999		  FreeBSD 11.1


Want to link to this manual page? Use this URL:

home | help