.\"	$OpenBSD: rmd160.3,v 1.26 2004/06/22 01:57:29 jfb Exp $
.\"
.\" Copyright (c) 1997, 2004 Todd C. Miller <Todd.Miller@courtesan.com>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.\" See http://www.esat.kuleuven.ac.be/~bosselae/ripemd160.html
.\"	for detailed information about RIPEMD-160.
.\"
.Dd April 29, 2004
.Dt RMD160 3
.Os
.Sh NAME
.Nm RMD160Init ,
.Nm RMD160Update ,
.Nm RMD160Pad ,
.Nm RMD160Final ,
.Nm RMD160Transform ,
.Nm RMD160End ,
.Nm RMD160File ,
.Nm RMD160FileChunk ,
.Nm RMD160Data
.Nd calculate the ``RIPEMD-160'' message digest
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <rmd160.h>
.Ft void
.Fn RMD160Init "RMD160_CTX *context"
.Ft void
.Fn RMD160Update "RMD160_CTX *context" "const u_int8_t *data" "u_int32_t nbytes"
.Ft void
.Fn RMD160Pad "RMD160_CTX *context"
.Ft void
.Fn RMD160Final "u_int8_t digest[RMD160_DIGEST_LENGTH]" "RMD160_CTX *context"
.Ft void
.Fn RMD160Transform "u_int32_t state[5]" "const u_int8_t block[RMD160_BLOCK_LENGTH]"
.Ft "char *"
.Fn RMD160End "RMD160_CTX *context" "char *buf"
.Ft "char *"
.Fn RMD160File "const char *filename" "char *buf"
.Ft "char *"
.Fn RMD160FileChunk "const char *filename" "char *buf" "off_t offset" "off_t length"
.Ft "char *"
.Fn RMD160Data "const u_int8_t *data" "size_t len" "char *buf"
.Sh DESCRIPTION
The RMD160 functions implement the 160-bit RIPE message digest hash algorithm
(RMD-160).
RMD-160 is used to generate a condensed representation
of a message called a message digest.
The algorithm takes a
message less than 2^64 bits as input and produces a 160-bit digest
suitable for use as a digital signature.
.Pp
The RMD160 functions are considered to be more secure than the
.Xr md4 3
and
.Xr md5 3
functions and at least as secure as the
.Xr sha1 3
function.
All share a similar interface.
.Pp
The
.Fn RMD160Init
function initializes a RMD160_CTX
.Ar context
for use with
.Fn RMD160Update ,
and
.Fn RMD160Final .
The
.Fn RMD160Update
function adds
.Ar data
of length
.Ar nbytes
to the RMD160_CTX specified by
.Ar context .
.Fn RMD160Final
is called when all data has been added via
.Fn RMD160Update
and stores a message digest in the
.Ar digest
parameter.
.Pp
The
.Fn RMD160Pad
function can be used to apply padding to the message digest as in
.Fn RMD160Final ,
but the current context can still be used with
.Fn RMD160Update .
.Pp
The
.Fn RMD160Transform
function is used by
.Fn RMD160Update
to hash 512-bit blocks and forms the core of the algorithm.
Most programs should use the interface provided by
.Fn RMD160Init ,
.Fn RMD160Update
and
.Fn RMD160Final
instead of calling
.Fn RMD160Transform
directly.
.Pp
The
.Fn RMD160End
function is a front end for
.Fn RMD160Final
which converts the digest into an
.Tn ASCII
representation of the 160 bit digest in hexadecimal.
.Pp
The
.Fn RMD160File
function calculates the digest for a file and returns the result via
.Fn RMD160End .
If
.Fn RMD160File
is unable to open the file a NULL pointer is returned.
.Pp
.Fn RMD160FileChunk
behaves like
.Fn RMD160File
but calculates the digest only for that portion of the file starting at
.Fa offset
and continuing for
.Fa length
bytes or until end of file is reached, whichever comes first.
A zero
.Fa length
can be specified to read until end of file.
A negative
.Fa length
or
.Fa offset
will be ignored.
.Pp
The
.Fn RMD160Data
function
calculates the digest of an arbitrary string and returns the result via
.Fn RMD160End .
.Pp
For each of the
.Fn RMD160End ,
.Fn RMD160File ,
and
.Fn RMD160Data
functions the
.Ar buf
parameter should either be a string of at least 41 characters in
size or a NULL pointer.
In the latter case, space will be dynamically allocated via
.Xr malloc 3
and should be freed using
.Xr free 3
when it is no longer needed.
.Sh EXAMPLES
The follow code fragment will calculate the digest for
the string "abc" which is ``0x8eb208f7e05d987a9b044a8e98c6b087f15a0bfc''.
.Bd -literal -offset indent
RMD160_CTX rmd;
u_int8_t results[RMD160_DIGEST_LENGTH];
char *buf;
int n;

buf = "abc";
n = strlen(buf);
RMD160Init(&rmd);
RMD160Update(&rmd, (u_int8_t *)buf, n);
RMD160Final(results, &rmd);

/* Print the digest as one long hex value */
printf("0x");
for (n = 0; n < RMD160_DIGEST_LENGTH; n++)
	printf("%02x", results[n]);
putchar('\en');
.Ed
.Pp
Alternately, the helper functions could be used in the following way:
.Bd -literal -offset indent
RMD160_CTX rmd;
u_int8_t output[RMD160_DIGEST_STRING_LENGTH];
char *buf = "abc";

printf("0x%s\en", RMD160Data(buf, strlen(buf), output));
.Ed
.Sh SEE ALSO
.Xr cksum 1 ,
.Xr rmd160 1 ,
.Xr md4 3 ,
.Xr md5 3 ,
.Xr sha1 3 ,
.Xr sha2 3
.Rs
.%A H. Dobbertin, A. Bosselaers, B. Preneel
.%T RIPEMD-160, a strengthened version of RIPEMD
.Re
.Rs
.%T Information technology - Security techniques - Hash-functions - Part 3: Dedicated hash-functions
.%O ISO/IEC 10118-3
.Re
.Rs
.%A H. Dobbertin, A. Bosselaers, B. Preneel
.%T The RIPEMD-160 cryptographic hash function
.%J Dr. Dobb's Journal
.%V Vol. 22, No. 1
.%D January 1997
.%P pp. 24-28
.Re
.Sh HISTORY
The RMD-160 functions appeared in
.Ox 2.1 .
.Sh AUTHORS
This implementation of RMD-160 was written by Markus Friedl.
.Pp
The
.Fn RMD160End ,
.Fn RMD160File ,
.Fn RMD160FileChunk ,
and
.Fn RMD160Data
helper functions are derived from code written by Poul-Henning Kamp.
.Sh CAVEATS
If a message digest is to be copied to a multi-byte type (ie:
an array of five 32-bit integers) it will be necessary to
perform byte swapping on little endian machines such as the i386, alpha,
and vax.