minix/man/man3/md5.3
2010-07-16 00:06:00 +00:00

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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
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.\" $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.