LIBRARY

Lb libmd

SYNOPSIS

In sys/types.h In md4.h Ft void Fn MD4Init MD4_CTX *context Ft void Fn MD4Update MD4_CTX *context const uint8_t *data size_t len Ft void Fn MD4Pad MD4_CTX *context Ft void Fn MD4Final uint8_t digest[MD4_DIGEST_LENGTH] MD4_CTX *context Ft void Fn MD4Transform uint32_t state[4] uint8_t block[MD4_BLOCK_LENGTH] Ft char * Fn MD4End MD4_CTX *context char *buf Ft char * Fn MD4File const char *filename char *buf Ft char * Fn MD4FileChunk const char *filename char *buf off_t offset off_t length Ft char * Fn MD4Data const uint8_t *data size_t len char *buf

DESCRIPTION

The MD4 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 Fn MD4Init , Fn MD4Update , and Fn MD4Final functions are the core functions. Allocate an MD4_CTX, initialize it with Fn MD4Init , run over the data with Fn MD4Update , and finally extract the result using Fn MD4Final .

The Fn MD4Pad function can be used to apply padding to the message digest as in Fn MD4Final , but the current context can still be used with Fn MD4Update .

The Fn MD4Transform function is used by Fn MD4Update to hash 512-bit blocks and forms the core of the algorithm. Most programs should use the interface provided by Fn MD4Init , Fn MD4Update and Fn MD4Final instead of calling Fn MD4Transform directly.

Fn MD4End is a wrapper for Fn MD4Final which converts the return value to an MD4_DIGEST_STRING_LENGTH-character (including the terminating '\0') ASCII string which represents the 128 bits in hexadecimal.

Fn MD4File calculates the digest of a file, and uses Fn MD4End to return the result. If the file cannot be opened, a null pointer is returned.

Fn MD4FileChunk behaves like Fn MD4File but calculates the digest only for that portion of the file starting at Fa offset and continuing for Fa length bytes or until end of file is reached, whichever comes first. A zero Fa length can be specified to read until end of file. A negative Fa length or Fa offset will be ignored. Fn MD4Data calculates the digest of a chunk of data in memory, and uses Fn MD4End to return the result.

When using Fn MD4End , Fn MD4File , Fn MD4FileChunk , or Fn MD4Data , 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 MD4_DIGEST_STRING_LENGTH characters of buffer space.

HISTORY

These functions appeared in Ox 2.0 and Nx 1.3 .

AUTHORS

The original MD4 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 Fn MD4End , Fn MD4File , Fn MD4FileChunk , and Fn MD4Data helper functions are derived from code written by Poul-Henning Kamp.