MDX(3)

NAME
MDXInit, MDXUpdate, MDXPad, MDXFinal, MDXTransform, MDXEnd, MDXFile, MDXFileChunk, MDXData - calculate the RSA Data Security, Inc., ``MDX'' message digest

SYNOPSIS
#include <sys/types.h>
#include <mdX.h>
void
MDXInit(MDX_CTX *context);
void
MDXUpdate(MDX_CTX *context, const u_int8_t *data, size_t len);
void
MDXPad(MDX_CTX *context);
void
MDXFinal(u_int8_t digest[MDX_DIGEST_LENGTH], MDX_CTX *context);
void
MDXTransform(u_int32_t state[4], u_int8_t block[MDX_BLOCK_LENGTH]);
char *
MDXEnd(MDX_CTX *context, char *buf);
char *
MDXFile(const char *filename, char *buf);
char *
MDXFileChunk(const char *filename, char *buf, off_t offset, off_t length);
char *
MDXData(const u_int8_t *data, size_t len, char *buf);

DESCRIPTION
The MDX 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 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 MDXInit(), MDXUpdate(), and MDXFinal() functions are the core functions. Allocate an MDX_CTX, initialize it with MDXInit(), run over the data with MDXUpdate(), and finally extract the result using MDXFinal().

The MDXPad() function can be used to apply padding to the message digest as in MDXFinal(), but the current context can still be used with MDXUpdate().

The MDXTransform() function is used by MDXUpdate() to hash 512-bit blocks and forms the core of the algorithm. Most programs should use the interface provided by MDXInit(), MDXUpdate() and MDXFinal() instead of calling MDXTransform() directly.

MDXEnd() is a wrapper for MDXFinal() which converts the return value to an MDX_DIGEST_STRING_LENGTH-character (including the terminating '\0') ASCII string which represents the 128 bits in hexadecimal.

MDXFile() calculates the digest of a file, and uses MDXEnd() to return the result. If the file cannot be opened, a null pointer is returned.

MDXFileChunk() behaves like MDXFile() 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. MDXData() calculates the digest of a chunk of data in memory, and uses MDXEnd() to return the result.

When using MDXEnd(), MDXFile(), MDXFileChunk(), or MDXData(), 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 MDX_DIGEST_STRING_LENGTH characters of buffer space.

SEE ALSO
cksum(1), md5(1), mdY(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
These functions appeared in OpenBSD 2.0.

AUTHORS
The original MDX 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 MDXEnd(), MDXFile(), MDXFileChunk(), and MDXData() 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.