MDX(3)

NAME
MDXInit, MDXUpdate, MDXFinal, MDXEnd, MDXFile, 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 unsigned char *data, unsigned int len);
void
MDXFinal(unsigned char digest[16], MDX_CTX *context);
char *
MDXEnd(MDX_CTX *context, char *buf);
char *
MDXFile(char *filename, char *buf);
char *
MDXData(const unsigned char *data, unsigned int 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.

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''. When in doubt, use MD5.

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().

MDXEnd() is a wrapper for MDXFinal() which converts the return value to a 33-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. MDXData() calculates the digest of a chunk of data in memory, and uses MDXEnd() to return the result.

When using MDXEnd(), MDXFile(), 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 33 characters of buffer space.

SEE ALSO
md2(3), md4(3), md5(3) B. Kaliski, The MD2 Message-Digest Algorithm, RFC 1319. 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.

AUTHOR
The original MDX routines were developed by RSA Data Security, Inc., and published in the above references. This code is derived directly from these implementations by Poul-Henning Kamp <phk@login.dkuug.dk>

Phk ristede runen.

HISTORY
These functions appeared in FreeBSD 2.0.

BUGS
No method is known to exist which finds two files having the same hash value, nor to find a file with a specific hash value. There is on the other hand no guarantee that such a method doesn't exist.

MD2 has only been licensed for use in Privacy Enhanced Mail. Use MD4 or MD5 if that isn't what you're doing.

COPYRIGHT