NAME

       MD5Init,  MD5Update,  MD5Pad,  MD5Final, MD5Transform, MD5End, MD5File, MD5FileChunk, MD5Data — calculate
       the RSA Data Security, Inc., “MD5” message digest

LIBRARY

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

SYNOPSIS

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

       void
       MD5Init(MD5_CTX *context);

       void
       MD5Update(MD5_CTX *context, const uint8_t *data, size_t len);

       void
       MD5Pad(MD5_CTX *context);

       void
       MD5Final(uint8_t digest[MD5_DIGEST_LENGTH], MD5_CTX *context);

       void
       MD5Transform(uint32_t state[4], uint8_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 uint8_t *data, size_t len, char *buf);

DESCRIPTION

       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 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  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 '\0') 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

       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  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

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

Debian                                            July 13, 2010                                           MD5(3)