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


.\"

.\" Copyright (c) 2000 Poul-Henning Kamp <phk@FreeBSD.org>

.\"

.\" Permission to use, copy, modify, and distribute this software for any

.\" purpose with or without fee is hereby granted, provided that the above

.\" copyright notice and this permission notice appear in all copies.

.\"

.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES

.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF

.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR

.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES

.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN

.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF

.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

.\"

.\" 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: MD5Init.3,v 1.1 2019/08/30 22:20:43 deraadt Exp $

.\"

.Dd $Mdocdate: August 30 2019 $

.Dt MD5INIT 3

.Os

.Sh NAME

.Nm MD5Init ,

.Nm MD5Update ,

.Nm MD5Pad ,

.Nm MD5Final ,

.Nm MD5Transform ,

.Nm MD5End ,

.Nm MD5File ,

.Nm MD5FileChunk ,

.Nm MD5Data

.Nd calculate MD5 message digest

.Sh SYNOPSIS

.In sys/types.h

.In md5.h

.Ft void

.Fn MD5Init "MD5_CTX *context"

.Ft void

.Fn MD5Update "MD5_CTX *context" "const u_int8_t *data" "size_t len"

.Ft void

.Fn MD5Pad "MD5_CTX *context"

.Ft void

.Fn MD5Final "u_int8_t digest[MD5_DIGEST_LENGTH]" "MD5_CTX *context"

.Ft void

.Fn MD5Transform "u_int32_t state[4]" "u_int8_t block[MD5_BLOCK_LENGTH]"

.Ft "char *"

.Fn MD5End "MD5_CTX *context" "char *buf"

.Ft "char *"

.Fn MD5File "const char *filename" "char *buf"

.Ft "char *"

.Fn MD5FileChunk "const char *filename" "char *buf" "off_t offset" "off_t length"

.Ft "char *"

.Fn MD5Data "const u_int8_t *data" "size_t len" "char *buf"

.Sh DESCRIPTION

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

.Dq fingerprint

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

.Pp

MD5 has been broken; it should only be used where necessary for

backward compatibility.

The attack on MD5 is in the nature of finding

.Dq collisions

\(em 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 MD5Init ,

.Fn MD5Update ,

and

.Fn MD5Final

functions are the core functions.

Allocate an

.Vt MD5_CTX ,

initialize it with

.Fn MD5Init ,

run over the data with

.Fn MD5Update ,

and finally extract the result using

.Fn MD5Final .

.Pp

The

.Fn MD5Pad

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

.Fn MD5Final ,

but the current context can still be used with

.Fn MD5Update .

.Pp

The

.Fn MD5Transform

function is used by

.Fn MD5Update

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

Most programs should use the interface provided by

.Fn MD5Init ,

.Fn MD5Update

and

.Fn MD5Final

instead of calling

.Fn MD5Transform

directly.

.Pp

.Fn MD5End

is a wrapper for

.Fn MD5Final

which converts the return value to an MD5_DIGEST_STRING_LENGTH-character

(including the terminating '\e0')

ASCII string which represents the 128 bits in hexadecimal.

.Pp

.Fn MD5File

calculates the digest of a file, and uses

.Fn MD5End

to return the result.

If the file cannot be opened, a null pointer is returned.

.Pp

.Fn MD5FileChunk

behaves like

.Fn MD5File

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 MD5Data

calculates the digest of a chunk of data in memory, and uses

.Fn MD5End

to return the result.

.Pp

When using

.Fn MD5End ,

.Fn MD5File ,

.Fn MD5FileChunk ,

or

.Fn MD5Data ,

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 MD5_DIGEST_STRING_LENGTH

characters of buffer space.

.Sh SEE ALSO

.Xr cksum 1 ,

.Xr md5 1 ,

.Xr RMD160Init 3 ,

.Xr SHA1INIT 3 ,

.Xr SHA256INIT 3

.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 April 1992

.%R RFC 1321

.%T The MD5 Message Digest Algorithm

.Re

.Sh HISTORY

These functions appeared in

.Ox 2.0 .

.Sh AUTHORS

.An -nosplit

The original MD5 routines were developed by

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

This code is derived from a public domain implementation written by

.An Colin Plumb .

.Pp

The

.Fn MD5End ,

.Fn MD5File ,

.Fn MD5FileChunk ,

and

.Fn MD5Data

helper functions are derived from code written by

.An Poul-Henning Kamp .

.Sh BUGS

Collisions have been found for the full version of MD5.

The use of the SHA2 functions is recommended instead.