.\"
.\" ----------------------------------------------------------------------------
.\" "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: md5.3,v 1.10 2007/05/31 19:19:29 jmc Exp $
.\"
.Dd $Mdocdate: May 31 2007 $
.Dt MD5 3
.Os
.Sh NAME
.Nm MD5Init ,
.Nm MD5Update ,
.Nm MD5Final ,
.Nm MD5End ,
.Nm MD5File ,
.Nm MD5Data
.Nd calculate the RSA Data Security, Inc., ``MD5'' message digest
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <minix/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 MD5Final "u_int8_t digest[MD5_DIGEST_LENGTH]" "MD5_CTX *context"
.Ft "char *"
.Fn MD5End "MD5_CTX *context" "char *buf"
.Ft "char *"
.Fn MD5File "const char *filename" "char *buf"
.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
The
.Fn MD5Init ,
.Fn MD5Update ,
and
.Fn MD5Final
functions are the core functions.
Allocate an MD5_CTX, initialize it with
.Fn MD5Init ,
run over the data with
.Fn MD5Update ,
and finally extract the result using
.Fn MD5Final .
.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')
.Tn 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 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 ,
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.
.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 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 BUGS
Collisions have been found for the full version of MD5.