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

     MD5Init, MD5Update, MD5Pad, MD5Final, MD5End, MD5File, MD5FileChunk,
     MD5Data - calculate 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 void *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 *
     MD5FileChunk(const char *filename, char *buf, off_t offset,
         off_t length);

     char *
     MD5Data(const void *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
     ``fingerprint'' of the input-data, which does not disclose the actual

     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
     functions.  Allocate an MD5_CTX, initialize it with MD5Init(), run over
     the data with MD5Update(), and finally extract the result using

     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.

     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.

     These functions appeared in FreeBSD 2.0.

     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.

     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
     documentation and/or software.

FreeBSD 11.0-PRERELEASE        February 11, 1999       FreeBSD 11.0-PRERELEASE


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