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MD5(3bsd) | 3bsd | MD5(3bsd) |
NAME¶
MD5Init
,
MD5Update
,
MD5Pad
,
MD5Final
,
MD5Transform
,
MD5End
,
MD5File
,
MD5FileChunk
,
MD5Data
—
calculate the RSA Data Security, Inc., ``MD5''
message digest
LIBRARY¶
library “libbsd”SYNOPSIS¶
#include
<sys/types.h>
#include
<bsd/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¶
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. 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. TheMD5Init
(),
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¶
cksum(1), md5(1), adler32(3), md4(3), rmd160(3), sfv(3), sha1(3), sha2(3), suma(3), tiger(3), whirlpool(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¶
These functions appeared in OpenBSD 2.0.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. TheMD5End
(),
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 as well as strong attacks against the SHA-0 and SHA-1 family. The use of sha2(3), or rmd160(3) is recommended instead.April 29, 2004 | Debian |