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"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
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$Id: mdX.3,v 1.14 1999/02/11 20:31:49 wollman Exp $
.Dd February 11, 1999 .Dt MDX 3 .Os FreeBSD 2 .Sh NAME .Nm MDXInit , .Nm MDXUpdate , .Nm MDXPad , .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 MDXPad "MDX_CTX *context" .Ft void .Fn MDXFinal "unsigned char digest[16]" "MDX_CTX *context" .Ft "char *" .Fn MDXEnd "MDX_CTX *context" "char *buf" .Ft "char *" .Fn MDXFile "const char *filename" "char *buf" .Ft "char *" .Fn MDXData "const 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.
p 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 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.
p 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 .
p .Fn MDXPad can be used to pad message data in same way as done by .Fn MDXFinal without terminating calculation.
p .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.
p .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.
p
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 md2 3 ,
.Xr md4 3 ,
.Xr md5 3 ,
.Xr sha 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
p Phk ristede runen. .Sh HISTORY These functions appeared in .Fx 2.0 . .Sh 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.
p 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