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MD4Data(3)


NAME

     MD4Init, MD4Update, MD4Pad, MD4Final, MD4Transform, MD4End, MD4File,
     MD4FileChunk, MD4Data — calculate the RSA Data Security, Inc., “MD4”
     message digest

LIBRARY

     library “libmd”

SYNOPSIS

     #include <sys/types.h>
     #include <md4.h>

     void
     MD4Init(MD4_CTX *context);

     void
     MD4Update(MD4_CTX *context, const uint8_t *data, size_t len);

     void
     MD4Pad(MD4_CTX *context);

     void
     MD4Final(uint8_t digest[MD4_DIGEST_LENGTH], MD4_CTX *context);

     void
     MD4Transform(uint32_t state[4], uint8_t block[MD4_BLOCK_LENGTH]);

     char *
     MD4End(MD4_CTX *context, char *buf);

     char *
     MD4File(const char *filename, char *buf);

     char *
     MD4FileChunk(const char *filename, char *buf, off_t offset,
     off_t length);

     char *
     MD4Data(const uint8_t *data, size_t len, char *buf);

DESCRIPTION

     The MD4 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
     middle.  MD2 can only be used for Privacy-Enhanced Mail.  MD4 has been
     criticized for being too weak, so MD5 was developed in response as ``MD4
     with safety-belts''.  MD4 and MD5 have been broken; they should only be
     used where necessary for backward compatibility.  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 MD4Init(), MD4Update(), and MD4Final() functions are the core
     functions.  Allocate an MD4_CTX, initialize it with MD4Init(), run over
     the data with MD4Update(), and finally extract the result using
     MD4Final().

     The MD4Pad() function can be used to apply padding to the message digest
     as in MD4Final(), but the current context can still be used with
     MD4Update().

     The MD4Transform() function is used by MD4Update() to hash 512-bit blocks
     and forms the core of the algorithm.  Most programs should use the
     interface provided by MD4Init(), MD4Update() and MD4Final() instead of
     calling MD4Transform() directly.

     MD4End() is a wrapper for MD4Final() which converts the return value to
     an MD4_DIGEST_STRING_LENGTH-character (including the terminating '\0')
     ASCII string which represents the 128 bits in hexadecimal.

     MD4File() calculates the digest of a file, and uses MD4End() to return
     the result.  If the file cannot be opened, a null pointer is returned.

     MD4FileChunk() behaves like MD4File() but calculates the digest only for
     that portion of the file starting at offset and continuing for length
     bytes or until end of file is reached, whichever comes first.  A zero
     length can be specified to read until end of file.  A negative length or
     offset will be ignored.  MD4Data() calculates the digest of a chunk of
     data in memory, and uses MD4End() to return the result.

     When using MD4End(), MD4File(), MD4FileChunk(), or MD4Data(), 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 MD4_DIGEST_STRING_LENGTH characters of buffer space.

SEE ALSO

     md2(3), md4(3), md5(3), rmd160(3), sha1(3), sha2(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 MD4 and MD5", RSA Laboratories
     Bulletin, 4, November 12, 1996.

     Hans Dobbertin, Cryptanalysis of MD5 Compress.

HISTORY

     These functions appeared in OpenBSD 2.0 and NetBSD 1.3.

AUTHORS

     The original MD4 routines were developed by RSA Data Security, Inc., and
     published in the above references.  This code is derived from a public
     domain implementation written by Colin Plumb.

     The MD4End(), MD4File(), MD4FileChunk(), and MD4Data() helper functions
     are derived from code written by Poul-Henning Kamp.

BUGS

     Collisions have been found for the full versions of both MD4 and MD5.
     The use of sha2(3) is recommended instead.



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