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MD5(3)

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NAME    [Toc]    [Back]

     MD5Init, MD5Update, MD5Pad, MD5Final, MD5Transform,  MD5End,
MD5File,
     MD5FileChunk,  MD5Data  -  calculate  the RSA Data Security,
Inc., ``MD5''
     message digest

SYNOPSIS    [Toc]    [Back]

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

     void
     MD5Init(MD5_CTX *context);

     void
     MD5Update(MD5_CTX *context,  const  u_int8_t  *data,  size_t
len);

     void
     MD5Pad(MD5_CTX *context);

     void
     MD5Final(u_int8_t     digest[MD5_DIGEST_LENGTH],     MD5_CTX
*context);

     void
     MD5Transform(u_int32_t          state[4],           u_int8_t
block[MD5_BLOCK_LENGTH]);

     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 u_int8_t *data, size_t len, char *buf);

DESCRIPTION    [Toc]    [Back]

     The MD5 functions calculate a 128-bit cryptographic checksum
(digest) for
     any number of input bytes.  A cryptographic  checksum  is  a
one-way hashfunction,
  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.


     MD4 has been broken; it should only be used where  necessary
for backward
     compatibility.   MD5  has  not yet (1999-02-11) been broken,
but recent attacks
 have cast some doubt on its security properties.   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
MD5Final().

     The  MD5Pad()  function  can be used to apply padding to the
message digest
     as in MD5Final(), but the current context can still be  used
with
     MD5Update().

     The  MD5Transform()  function is used by MD5Update() to hash
512-bit blocks
     and forms the core of the algorithm.  Most  programs  should
use the interface
  provided  by MD5Init(), MD5Update() and MD5Final() instead of calling
     MD5Transform() directly.

     MD5End() is a wrapper for MD5Final() which converts the  return value to
     an  MD5_DIGEST_STRING_LENGTH-character (including the terminating ' ')
     ASCII string which represents 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.

     MD5FileChunk() behaves like MD5File() 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.  MD5Data() calculates the digest  of
a chunk of
     data in memory, and uses MD5End() to return the result.

     When   using   MD5End(),   MD5File(),   MD5FileChunk(),   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  MD5_DIGEST_STRING_LENGTH  characters  of  buffer
space.

SEE ALSO    [Toc]    [Back]

      
      
     cksum(1), md5(1), md4(3), rmd160(3), sha1(3), sha2(3)

     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    [Toc]    [Back]

     These functions appeared in OpenBSD 2.0.

AUTHORS    [Toc]    [Back]

     The original MD5 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   MD5End(),  MD5File(),  MD5FileChunk(),  and  MD5Data()
helper functions
     are derived from code written by Poul-Henning Kamp.

BUGS    [Toc]    [Back]

     Collisions have been found for the full versions of both MD4
and MD5.
     The use of sha1(3), sha2(3), or rmd160(3) is recommended instead.

OpenBSD     3.6                          April      29,      2004
[ Back ]
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