Fincer
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openntpd-openbsd
mirror of https://github.com/Fincer/openntpd-openbsd


.\"

.\" ----------------------------------------------------------------------------

.\" "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 2013/06/05 03:39:22 tedu Exp $

.\"

.Dd $Mdocdate: June 5 2013 $

.Dt MDX 3

.Os

.Sh NAME

.Nm MDXInit ,

.Nm MDXUpdate ,

.Nm MDXPad ,

.Nm MDXFinal ,

.Nm MDXTransform ,

.Nm MDXEnd ,

.Nm MDXFile ,

.Nm MDXFileChunk ,

.Nm MDXData

.Nd calculate the RSA Data Security, Inc., ``MDX'' message digest

.Sh SYNOPSIS

.In sys/types.h

.In mdX.h

.Ft void

.Fn MDXInit "MDX_CTX *context"

.Ft void

.Fn MDXUpdate "MDX_CTX *context" "const u_int8_t *data" "size_t len"

.Ft void

.Fn MDXPad "MDX_CTX *context"

.Ft void

.Fn MDXFinal "u_int8_t digest[MDX_DIGEST_LENGTH]" "MDX_CTX *context"

.Ft void

.Fn MDXTransform "u_int32_t state[4]" "u_int8_t block[MDX_BLOCK_LENGTH]"

.Ft "char *"

.Fn MDXEnd "MDX_CTX *context" "char *buf"

.Ft "char *"

.Fn MDXFile "const char *filename" "char *buf"

.Ft "char *"

.Fn MDXFileChunk "const char *filename" "char *buf" "off_t offset" "off_t length"

.Ft "char *"

.Fn MDXData "const u_int8_t *data" "size_t 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

.Dq fingerprint

of the input-data, which doesn't disclose the actual input.

.Pp

MD4 and MD5 have been broken; they should only be used where necessary for

backward compatibility.

The attacks on both MD4 and MD5

are both in the nature of finding

.Dq 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 .

.Pp

The

.Fn MDXPad

function can be used to apply padding to the message digest as in

.Fn MDXFinal ,

but the current context can still be used with

.Fn MDXUpdate .

.Pp

The

.Fn MDXTransform

function is used by

.Fn MDXUpdate

to hash 512-bit blocks and forms the core of the algorithm.

Most programs should use the interface provided by

.Fn MDXInit ,

.Fn MDXUpdate

and

.Fn MDXFinal

instead of calling

.Fn MDXTransform

directly.

.Pp

.Fn MDXEnd

is a wrapper for

.Fn MDXFinal

which converts the return value to an MDX_DIGEST_STRING_LENGTH-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.

.Pp

.Fn MDXFileChunk

behaves like

.Fn MDXFile

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 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 ,

.Fn MDXFileChunk ,

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 MDX_DIGEST_STRING_LENGTH

characters of buffer space.

.Sh SEE ALSO

.Xr cksum 1 ,

.Xr md5 1 ,

.Xr mdY 3 ,

.Xr rmd160 3 ,

.Xr sha1 3 ,

.Xr sha2 3

.Rs

.%A RSA Laboratories

.%T Frequently Asked Questions About today's Cryptography

.%U http://www.rsa.com/rsalabs/faq/

.Re

.Rs

.%A H. Dobbertin

.%D 1995

.%J CryptoBytes

.%N 1(3):5

.%T Alf Swindles Ann

.Re

.Rs

.%A MJ. B. Robshaw

.%D November 12, 1996

.%J RSA Laboratories Bulletin

.%N 4

.%T On Recent Results for MD4 and MD5

.Re

.Rs

.%A Hans Dobbertin

.%T Cryptanalysis of MD5 Compress

.Re

.Sh STANDARDS

.Rs

.%A R. Rivest

.%D October 1990

.%R RFC 1186

.%T The MD4 Message Digest Algorithm

.Re

.Pp

.Rs

.%A R. Rivest

.%D April 1992

.%R RFC 1321

.%T The MD5 Message Digest Algorithm

.Re

.Sh HISTORY

These functions appeared in

.Ox 2.0 .

.Sh AUTHORS

The original MDX routines were developed by

.Tn RSA

Data Security, Inc., and published in the above references.

This code is derived from a public domain implementation written by Colin Plumb.

.Pp

The

.Fn MDXEnd ,

.Fn MDXFile ,

.Fn MDXFileChunk ,

and

.Fn MDXData

helper functions are derived from code written by Poul-Henning Kamp.

.Sh BUGS

Collisions have been found for the full versions of both MD4 and MD5.

The use of

.Xr sha2 3

								is recommended instead.