NAME
MD5Init,
MD5Update,
MD5Final,
MD5End,
MD5File,
MD5Data —
calculate the RSA Data Security, Inc., “MD5”
message digest
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/types.h>
#include <md5.h>
void
MD5Init(
MD5_CTX
*context);
void
MD5Update(
MD5_CTX
*context,
const unsigned
char *data,
unsigned int
len);
void
MD5Final(
unsigned
char digest[16],
MD5_CTX
*context);
char *
MD5End(
MD5_CTX
*context,
char *buf);
char *
MD5File(
const
char *filename,
char
*buf);
char *
MD5Data(
const
unsigned char *data,
unsigned int 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''. When
in doubt, use MD5.
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().
MD5End() 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.
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.
MD5Data() 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.
SEE ALSO
md2(3),
md4(3),
md5(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.
HISTORY
These functions appeared in
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 directly from these
implementations by Poul-Henning Kamp
⟨
phk@login.dkuug.dk
⟩
Phk ristede runen.
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.
COPYRIGHT
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.