131 lines
3.1 KiB
Groff
131 lines
3.1 KiB
Groff
.\"
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.\" ----------------------------------------------------------------------------
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.\" "THE BEER-WARE LICENSE" (Revision 42):
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.\" <phk@login.dkuug.dk> wrote this file. As long as you retain this notice you
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.\" can do whatever you want with this stuff. If we meet some day, and you think
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.\" this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
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.\" ----------------------------------------------------------------------------
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.\"
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.\" $OpenBSD: md5.3,v 1.10 2007/05/31 19:19:29 jmc Exp $
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.\"
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.Dd $Mdocdate: May 31 2007 $
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.Dt MD5 3
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.Os
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.Sh NAME
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.Nm MD5Init ,
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.Nm MD5Update ,
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.Nm MD5Final ,
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.Nm MD5End ,
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.Nm MD5File ,
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.Nm MD5Data
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.Nd calculate the RSA Data Security, Inc., ``MD5'' message digest
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.Sh SYNOPSIS
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.Fd #include <sys/types.h>
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.Fd #include <minix/md5.h>
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.Ft void
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.Fn MD5Init "MD5_CTX *context"
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.Ft void
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.Fn MD5Update "MD5_CTX *context" "const u_int8_t *data" "size_t len"
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.Ft void
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.Fn MD5Final "u_int8_t digest[MD5_DIGEST_LENGTH]" "MD5_CTX *context"
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.Ft "char *"
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.Fn MD5End "MD5_CTX *context" "char *buf"
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.Ft "char *"
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.Fn MD5File "const char *filename" "char *buf"
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.Ft "char *"
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.Fn MD5Data "const u_int8_t *data" "size_t len" "char *buf"
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.Sh DESCRIPTION
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The MD5 functions calculate a 128-bit cryptographic checksum (digest)
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for any number of input bytes.
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A cryptographic checksum is a one-way
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hash-function, that is, you cannot find (except by exhaustive search)
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the input corresponding to a particular output.
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This net result is a
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.Dq fingerprint
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of the input-data, which doesn't disclose the actual input.
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.Pp
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The
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.Fn MD5Init ,
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.Fn MD5Update ,
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and
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.Fn MD5Final
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functions are the core functions.
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Allocate an MD5_CTX, initialize it with
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.Fn MD5Init ,
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run over the data with
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.Fn MD5Update ,
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and finally extract the result using
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.Fn MD5Final .
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.Pp
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.Fn MD5End
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is a wrapper for
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.Fn MD5Final
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which converts the return value to an MD5_DIGEST_STRING_LENGTH-character
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(including the terminating '\e0')
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.Tn ASCII
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string which represents the 128 bits in hexadecimal.
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.Pp
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.Fn MD5File
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calculates the digest of a file, and uses
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.Fn MD5End
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to return the result.
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If the file cannot be opened, a null pointer is returned.
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.Pp
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.Fn MD5Data
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calculates the digest of a chunk of data in memory, and uses
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.Fn MD5End
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to return the result.
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.Pp
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When using
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.Fn MD5End ,
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.Fn MD5File ,
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or
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.Fn MD5Data ,
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the
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.Ar buf
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argument can be a null pointer, in which case the returned string
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is allocated with
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.Xr malloc 3
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and subsequently must be explicitly deallocated using
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.Xr free 3
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after use.
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If the
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.Ar buf
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argument is non-null it must point to at least MD5_DIGEST_STRING_LENGTH
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characters of buffer space.
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.Rs
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.%A R. Rivest
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.%T The MD4 Message-Digest Algorithm
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.%O RFC 1186
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.Re
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.Rs
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.%A R. Rivest
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.%T The MD5 Message-Digest Algorithm
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.%O RFC 1321
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.Re
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.Rs
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.%A RSA Laboratories
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.%T Frequently Asked Questions About today's Cryptography
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.%O \&<http://www.rsa.com/rsalabs/faq/>
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.Re
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.Rs
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.%A H. Dobbertin
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.%T Alf Swindles Ann
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.%J CryptoBytes
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.%N 1(3):5
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.%D 1995
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.Re
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.Rs
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.%A MJ. B. Robshaw
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.%T On Recent Results for MD4 and MD5
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.%J RSA Laboratories Bulletin
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.%N 4
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.%D November 12, 1996
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.Re
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.Rs
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.%A Hans Dobbertin
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.%T Cryptanalysis of MD5 Compress
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.Re
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.Sh BUGS
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Collisions have been found for the full version of MD5.
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