MD5

Section: Misc. Reference Manual Pages (3bsd)
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NAME

MD5Init MD5Update MD5Pad MD5Final MD5Transform MD5End MD5File MD5FileChunk MD5Data - calculate the RSA Data Security, Inc., ``MD5'' message digest

LIBRARY

Lb libbsd

SYNOPSIS

In sys/types.h In md5.h (See libbsd(7) for include usage.) Ft void Fn MD5Init MD5_CTX *context Ft void Fn MD5Update MD5_CTX *context const uint8_t *data size_t len Ft void Fn MD5Pad MD5_CTX *context Ft void Fn MD5Final uint8_t digest[MD5_DIGEST_LENGTH] MD5_CTX *context Ft void Fn MD5Transform uint32_t state[4] uint8_t block[MD5_BLOCK_LENGTH] Ft char * Fn MD5End MD5_CTX *context char *buf Ft char * Fn MD5File const char *filename char *buf Ft char * Fn MD5FileChunk const char *filename char *buf off_t offset off_t length Ft char * Fn MD5Data const uint8_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.

The Fn MD5Init , Fn MD5Update , and Fn MD5Final functions are the core functions. Allocate an MD5_CTX, initialize it with Fn MD5Init , run over the data with Fn MD5Update , and finally extract the result using Fn MD5Final .

The Fn MD5Pad function can be used to apply padding to the message digest as in Fn MD5Final , but the current context can still be used with Fn MD5Update .

The Fn MD5Transform function is used by Fn MD5Update to hash 512-bit blocks and forms the core of the algorithm. Most programs should use the interface provided by Fn MD5Init , Fn MD5Update and Fn MD5Final instead of calling Fn MD5Transform directly.

Fn MD5End is a wrapper for Fn 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.

Fn MD5File calculates the digest of a file, and uses Fn MD5End to return the result. If the file cannot be opened, a null pointer is returned.

Fn MD5FileChunk behaves like Fn MD5File 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 MD5Data calculates the digest of a chunk of data in memory, and uses Fn MD5End to return the result.

When using Fn MD5End , Fn MD5File , Fn MD5FileChunk , or Fn 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.

HISTORY

These functions appeared in Ox 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.

The Fn MD5End , Fn MD5File , Fn MD5FileChunk , and Fn 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.

MD5