.\" .\" ---------------------------------------------------------------------------- .\" "THE BEER-WARE LICENSE" (Revision 42): .\" <phk@login.dkuug.dk> wrote this file. As long as you retain this notice you .\" can do whatever you want with this stuff. If we meet some day, and you think .\" this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp .\" ---------------------------------------------------------------------------- .\" .\" $OpenBSD: mdX.3,v 1.14 1999/10/08 10:55:27 espie Exp $ .\" .Dd October 9, 1996 .Dt MDX 3 .Os .Sh NAME .Nm MDXInit , .Nm MDXUpdate , .Nm MDXFinal , .Nm MDXEnd , .Nm MDXFile , .Nm MDXData .Nd calculate the RSA Data Security, Inc., ``MDX'' message digest .Sh SYNOPSIS .Fd #include <sys/types.h> .Fd #include <mdX.h> .Ft void .Fn MDXInit "MDX_CTX *context" .Ft void .Fn MDXUpdate "MDX_CTX *context" "const unsigned char *data" "unsigned int len" .Ft void .Fn MDXFinal "unsigned char digest[16]" "MDX_CTX *context" .Ft "char *" .Fn MDXEnd "MDX_CTX *context" "char *buf" .Ft "char *" .Fn MDXFile "char *filename" "char *buf" .Ft "char *" .Fn MDXData "unsigned char *data" "unsigned int len" "char *buf" .Sh 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. .Pp 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 shown to have severe vulnerabilities; 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. .Pp The .Fn MDXInit , .Fn MDXUpdate , and .Fn MDXFinal functions are the core functions. Allocate an MDX_CTX, initialize it with .Fn MDXInit , run over the data with .Fn MDXUpdate , and finally extract the result using .Fn MDXFinal . When a null pointer is passed to .Fn MDXFinal as first argument only the final padding will be applied and the current context can still be used with .Fn MDXUpdate . .Pp .Fn MDXEnd is a wrapper for .Fn MDXFinal which converts the return value to a 33-character (including the terminating '\e0') .Tn ASCII string which represents the 128 bits in hexadecimal. .Pp .Fn MDXFile calculates the digest of a file, and uses .Fn MDXEnd to return the result. If the file cannot be opened, a null pointer is returned. .Fn MDXData calculates the digest of a chunk of data in memory, and uses .Fn MDXEnd to return the result. .Pp When using .Fn MDXEnd , .Fn MDXFile , or .Fn MDXData , the .Ar buf argument can be a null pointer, in which case the returned string is allocated with .Xr malloc 3 and subsequently must be explicitly deallocated using .Xr free 3 after use. If the .Ar buf argument is non-null it must point to at least 33 characters of buffer space. .Sh SEE ALSO .Xr mdY 3 , .Xr rmd160 3 , .Xr sha1 3 .Rs .%A B. Kaliski .%T The MD2 Message-Digest Algorithm .%O RFC 1319 .Re .Rs .%A R. Rivest .%T The MD4 Message-Digest Algorithm .%O RFC 1186 .Re .Rs .%A R. Rivest .%T The MD5 Message-Digest Algorithm .%O RFC 1321 .Re .Rs .%A RSA Laboratories .%T Frequently Asked Questions About today's Cryptography .%O \&<http://www.rsa.com/rsalabs/faq/> .Re .Rs .%A H. Dobbertin .%T Alf Swindles Ann .%J CryptoBytes .%N 1(3):5 .%D 1995 .Re .Rs .%A MJ. B. Robshaw .%T On Recent Results for MD2, MD4 and MD5 .%J RSA Laboratories Bulletin .%N 4 .%D November 12, 1996 .Re .Rs .%A Hans Dobbertin .%T Cryptanalysis of MD5 Compress .Re .Sh AUTHOR The original MDX routines were developed by .Tn RSA Data Security, Inc., and published in the above references. This code is derived directly from these implementations by Poul-Henning Kamp .Aq Li phk@login.dkuug.dk .Pp Phk ristede runen. .Sh HISTORY These functions appeared in .Ox 2.0 . .Sh BUGS Hans Dobbertin has shown collisions for the full version of MD4 and found a collision in the compress function of MD5. The use of SHA or RIPEMD-160 is recommended instead. .Pp MD2 has only been licensed for use in Privacy Enhanced Mail. Use MD4 or MD5 if that isn't what you're doing. .Sh COPYRIGHT