.\" $NetBSD: tiger.3,v 1.4 2014/02/17 07:23:18 agc Exp $
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.\" Copyright (c) 2011 Alistair Crooks <agc@NetBSD.org>
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.Dd May 30, 2011
.Dt TIGER 3
.Os
.Sh NAME
.Nm TIGER_Init ,
.Nm TIGER_Update ,
.Nm TIGER_Final ,
.Nm TIGER_End ,
.Nm TIGER_File ,
.Nm TIGER_Data
.Nd calculate TIGER message digests
.Sh SYNOPSIS
.In tiger.h
.Ft void
.Fo TIGER_Init
.Fa "TIGER_CTX *context"
.Fc
.Ft void
.Fo TIGER_Update
.Fa "TIGER_CTX *context" "const uint8_t *data" "u_int len"
.Fc
.Ft void
.Fo TIGER_Final
.Fa "uint8_t digest[20]" "TIGER_CTX *context"
.Fc
.Ft "char *"
.Fo TIGER_End
.Fa "TIGER_CTX *context" "char *buf"
.Fc
.Ft "char *"
.Fo TIGER_File
.Fa "char *filename" "char *buf"
.Fc
.Ft "char *"
.Fo TIGER_Data
.Fa "uint8_t *data" "size_t len" "char *buf"
.Fc
.Sh DESCRIPTION
The TIGER functions calculate TIGER message digest functions,
as defined by Ross Anderson and Eli Biham.
The algorithm takes a
message less than 2^64 bits as input and produces a 192-bit digest
suitable for use as a digital signature.
.Pp
At the time of writing,
May 2011,
no attacks or pre-imaging have been discovered against the
.Nm
message digests, whilst the same cannot be said of
.Xr md5 3
or
.Xr sha1 3 .
.Pp
The
.Fn TIGER_Init
function initializes a TIGER_CTX
.Ar context
for use with
.Fn TIGER_Update ,
and
.Fn TIGER_Final .
The
.Fn TIGER_Update
function adds
.Ar data
of length
.Ar len
to the TIGER_CTX specified by
.Ar context .
.Fn TIGER_Final
is called when all data has been added via
.Fn TIGER_Update
and stores a message digest in the
.Ar digest
parameter.
When a
.Dv NULL
pointer is passed to
.Fn TIGER_Final
as first argument only the final padding will be applied and the
current context can still be used with
.Fn TIGER_Update .
.Pp
The core of the TIGER message digest is performed by
.Fn TIGER_Update .
Most programs should use the interface provided by
.Fn TIGER_Init ,
.Fn TIGER_Update ,
and
.Fn TIGER_Final .
.Pp
The
.Fn TIGER_End
function is a frontend for
.Fn TIGER_Final
which converts the digest into an
.Tn ASCII
representation of the 160 bit digest in hexadecimal.
.Pp
The
.Fn TIGER_File
function calculates the digest for a file and returns the result via
.Fn TIGER_End .
If
.Fn TIGER_File
is unable to open the file a
.Dv NULL
pointer is returned.
.Pp
The
.Fn TIGER_Data
function
calculates the digest of an arbitrary string and returns the result via
.Fn TIGER_End .
.Pp
For each of the
.Fn TIGER_End ,
.Fn TIGER_File ,
and
.Fn TIGER_Data
functions the
.Ar buf
parameter should either be a string of at least 41 characters in
size or a
.Dv 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
.Dq The quick brown fox jumps over the lazy dog ,
which is
.Dq 6d12a41e72e644f017b6f0e2f7b44c6285f06dd5d2c5b075 .
.Bd -literal -offset indent
TIGER_CTX tiger;
uint8_t results[24];
char *buf;
int n;

buf = "The quick brown fox jumps over the lazy dog";
n = strlen(buf);
TIGER_Init(\*[Am]tiger);
TIGER_Update(\*[Am]tiger, (uint8_t *)buf, n);
TIGER_Final(results, \*[Am]tiger);

/* Print the digest as one long hex value */
printf("0x");
for (n = 0; n \*[Lt] 24; n++)
	printf("%02x", results[n]);
putchar('\en');
.Ed
.Pp
Alternately, the helper functions could be used in the following way:
.Bd -literal -offset indent
TIGER_CTX tiger;
uint8_t output[49];
char *buf = "The quick brown fox jumps over the lazy dog";

printf("0x%s", TIGER_Data(buf, strlen(buf), output));
.Ed
.Sh SEE ALSO
.Xr md5 3 ,
.Xr sha1 3
.Rs
.%A Ross Anderson
.%A Eli Biham
.%T "Tiger \- A Fast New Hash Function"
.%B Proceedings of Fast Software Encryption 3, Cambridge
.%D 1996
.Re
.Sh HISTORY
The TIGER functions appeared in
.Nx 6.0 .
.Sh AUTHORS
.An -nosplit
This implementation of TIGER was adapted by
.An Alistair Crooks Aq Mt agc@NetBSD.org
from the original reference code.
.Pp
The
.Fn TIGER_End ,
.Fn TIGER_File ,
and
.Fn TIGER_Data
helper functions are derived from code written by Poul-Henning Kamp.
.Sh BUGS
All attempts have been made to optimise for the underlying hardware,
as well as to format the digest properly in an endian-neutral manner.
The author has no VAX hardware on which to test, and so it is not known
whether that platform is supported.