MD2(3) | Library Functions Manual | MD2(3) |
NAME¶
MD2Init
,
MD2Update
, MD2Pad
,
MD2Final
, MD2Transform
,
MD2End
, MD2File
,
MD2FileChunk
, MD2Data
— calculate the RSA Data Security, Inc.,
“MD2” message digest
LIBRARY¶
Message Digest (MD4, MD5, etc.) Support Library (libmd, -lmd)
SYNOPSIS¶
#include
<sys/types.h>
#include <md2.h>
void
MD2Init
(MD2_CTX
*context);
void
MD2Update
(MD2_CTX
*context, const uint8_t
*data, size_t
len);
void
MD2Pad
(MD2_CTX
*context);
void
MD2Final
(uint8_t
digest[MD2_DIGEST_LENGTH],
MD2_CTX *context);
void
MD2Transform
(uint32_t
state[4], uint8_t
block[MD2_BLOCK_LENGTH]);
char *
MD2End
(MD2_CTX
*context, char
*buf);
char *
MD2File
(const
char *filename, char
*buf);
char *
MD2FileChunk
(const
char *filename, char
*buf, off_t offset,
off_t length);
char *
MD2Data
(const
uint8_t *data, size_t
len, char
*buf);
DESCRIPTION¶
The MD2 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
MD2Init
(),
MD2Update
(),
and MD2Final
() functions are the core functions.
Allocate an MD2_CTX, initialize it with MD2Init
(),
run over the data with MD2Update
(), and finally
extract the result using MD2Final
().
The
MD2Pad
()
function can be used to apply padding to the message digest as in
MD2Final
(),
but the current context can still be used with
MD2Update
().
The
MD2Transform
()
function is used by
MD2Update
()
to hash 512-bit blocks and forms the core of the algorithm. Most programs
should use the interface provided by MD2Init
(),
MD2Update
() and MD2Final
()
instead of calling MD2Transform
() directly.
MD2End
()
is a wrapper for
MD2Final
()
which converts the return value to an MD2_DIGEST_STRING_LENGTH-character
(including the terminating '\0') ASCII string which represents the 128 bits
in hexadecimal.
MD2File
()
calculates the digest of a file, and uses MD2End
()
to return the result. If the file cannot be opened, a null pointer is
returned.
MD2FileChunk
()
behaves like MD2File
() 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.
MD2Data
()
calculates the digest of a chunk of data in memory, and uses
MD2End
() to return the result.
When using
MD2End
(),
MD2File
(), MD2FileChunk
(),
or MD2Data
(), 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 MD2_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 MD2 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 MD2End
(),
MD2File
(), MD2FileChunk
(),
and MD2Data
() 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.
July 13, 2010 | Linux 6.4.0-150600.23.17-default |