FreeBSD Man Pages

MD2FileChunk(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 unsigned char *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 unsigned char *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 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
     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 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.

     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 MD2, MD4 and MD5", RSA
     Laboratories Bulletin, 4, November 12, 1996.

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.

HISTORY

     These functions appeared in FreeBSD 2.0.

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 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) 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

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