.\" $NetBSD: md2.3,v 1.1 2005/09/24 20:51:14 elad Exp $
.\"
.\" ----------------------------------------------------------------------------
.\" "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
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.\"	from FreeBSD Id: mdX.3,v 1.7 1996/10/22 16:28:56 phk Exp
.\"
.Dd September 24, 2005
.Dt MD2 3
.Os
.Sh NAME
.Nm MD2Init ,
.Nm MD2Update ,
.Nm MD2Final ,
.Nm MD2End ,
.Nm MD2File ,
.Nm MD2Data
.Nd calculate the RSA Data Security, Inc.,
.Dq MD2
message digest
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/types.h
.In mdX.h
.Ft void
.Fn MD2Init "MD2_CTX *context"
.Ft void
.Fn MD2Update "MD2_CTX *context" "const unsigned char *data" "unsigned int len"
.Ft void
.Fn MD2Final "unsigned char digest[16]" "MD2_CTX *context"
.Ft "char *"
.Fn MD2End "MD2_CTX *context" "char *buf"
.Ft "char *"
.Fn MD2File "const char *filename" "char *buf"
.Ft "char *"
.Fn MD2Data "const unsigned char *data" "unsigned int len" "char *buf"
.Sh DESCRIPTION
The MD2 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 ``fingerprint'' of the input-data, which doesn't disclose the actual
input.
.Pp
The MD2 routines should not be used for any security-related purpose.
.Pp
The
.Fn MD2Init ,
.Fn MD2Update ,
and
.Fn MD2Final
functions are the core functions.
Allocate an MD2_CTX, initialize it with
.Fn MD2Init ,
run over the data with
.Fn MD2Update ,
and finally extract the result using
.Fn MD2Final .
.Pp
.Fn MD2End
is a wrapper for
.Fn MD2Final
which converts the return value to a 33-character
(including the terminating '\e0')
.Tn ASCII
string which represents the 128 bits in hexadecimal.
.Pp
.Fn MD2File
calculates the digest of a file, and uses
.Fn MD2End
to return the result.
If the file cannot be opened, a null pointer is returned.
.Fn MD2Data
calculates the digest of a chunk of data in memory, and uses
.Fn MD2End
to return the result.
.Pp
When using
.Fn MD2End ,
.Fn MD2File ,
or
.Fn MD2Data ,
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 33 characters of buffer space.
.Sh SEE ALSO
.Xr md2 3 ,
.Rs
.%A B. Kaliski
.%T The MD2 Message-Digest Algorithm
.%O RFC 1319
.Re
.Rs
.%A RSA Laboratories
.%T Frequently Asked Questions About today's Cryptography
.Re
.Sh HISTORY
These functions appeared in
.Nx 1.3 .
.Sh AUTHORS
The original MD2 routines were developed by
.Tn RSA
Data Security, Inc., and published in the above references.
This code is a public domain implementation by Andrew Brown.
.Sh BUGS
No method is known to exist which finds two files having the same hash value,
nor to find a file with a specific hash value.
There is on the other hand no guarantee that such a method doesn't exist.