MD2Update(3) calculate the RSA Data Security, Inc.,

Other Alias

MD2Init, MD2Pad, MD2Final, MD2Transform, MD2End, MD2File, MD2FileChunk, MD2Data


Lb libmd


In sys/types.h In md2.h Ft void Fn MD2Init MD2_CTX *context Ft void Fn MD2Update MD2_CTX *context const uint8_t *data size_t len Ft void Fn MD2Pad MD2_CTX *context Ft void Fn MD2Final uint8_t digest[MD2_DIGEST_LENGTH] MD2_CTX *context Ft void Fn MD2Transform uint32_t state[4] uint8_t block[MD2_BLOCK_LENGTH] Ft char * Fn MD2End MD2_CTX *context char *buf Ft char * Fn MD2File const char *filename char *buf Ft char * Fn MD2FileChunk const char *filename char *buf off_t offset off_t length Ft char * Fn MD2Data const uint8_t *data size_t len char *buf


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 Fn MD2Init , Fn MD2Update , and Fn MD2Final functions are the core functions. Allocate an MD2_CTX, initialize it with Fn MD2Init , run over the data with Fn MD2Update , and finally extract the result using Fn MD2Final .

The Fn MD2Pad function can be used to apply padding to the message digest as in Fn MD2Final , but the current context can still be used with Fn MD2Update .

The Fn MD2Transform function is used by Fn MD2Update to hash 512-bit blocks and forms the core of the algorithm. Most programs should use the interface provided by Fn MD2Init , Fn MD2Update and Fn MD2Final instead of calling Fn MD2Transform directly.

Fn MD2End is a wrapper for Fn 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.

Fn MD2File calculates the digest of a file, and uses Fn MD2End to return the result. If the file cannot be opened, a null pointer is returned.

Fn MD2FileChunk behaves like Fn MD2File 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 MD2Data calculates the digest of a chunk of data in memory, and uses Fn MD2End to return the result.

When using Fn MD2End , Fn MD2File , Fn MD2FileChunk , or Fn 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.


These functions appeared in Ox 2.0 and Nx 1.3 .


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 Fn MD2End , Fn MD2File , Fn MD2FileChunk , and Fn MD2Data helper functions are derived from code written by Poul-Henning Kamp.


Collisions have been found for the full versions of both MD4 and MD5. The use of sha2(3) is recommended instead.