MD5(3) BSD Library Functions Manual MD5(3)
MD5Init, MD5Update, MD5Pad, MD5Final, MD5End, MD5File, MD5FileChunk, MD5Data -- calculate the RSA Data Security, Inc., ``MD5'' message digest
Message Digest (MD4, MD5, etc.) Support Library (libmd, -lmd)
MD5Update(MD5_CTX *context, const void *data, unsigned int len);
MD5Final(unsigned char digest, MD5_CTX *context);
MD5End(MD5_CTX *context, char *buf);
MD5File(const char *filename, char *buf);
MD5FileChunk(const char *filename, char *buf, off_t offset, off_t length);
MD5Data(const void *data, unsigned int len, char *buf);
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 does not disclose the actual input.
MD4 is the fastest and MD5 is somewhat slower. MD4 has now been broken; it should only be used where necessary for backward compatibility.
MD5 has not yet (1999-02-11) been broken, but sufficient attacks have been made that its security is in some doubt. 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 MD5Init(), MD5Update(), and MD5Final() functions are the core functions. Allocate an MD5_CTX, initialize it with MD5Init(), run over the
data with MD5Update(), and finally extract the result using MD5Final().
The MD5Pad() function can be used to pad message data in same way as done by MD5Final() without terminating calculation.
The MD5End() function is a wrapper for MD5Final() which converts the return value to a 33-character (including the terminating '