.\" $NetBSD: md2.3,v 1.3 2018/12/17 08:18:06 wiz Exp $
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.\" "THE BEER-WARE LICENSE" (Revision 42):
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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') 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 md4 3 ,
.Xr md5 3 ,
.Xr openssl_MD2 3 ,
.Xr openssl_MD4 3 ,
.Xr openssl_MD5 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
.An -nosplit
The original MD2 routines were developed by
.An RSA Data Security, Inc. ,
and published in the above references.
This code is a public domain implementation by
.An 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.
