.\"	$OpenBSD: sha1.3,v 1.17 1999/10/06 14:55:29 espie Exp $
.\"
.\" Copyright (c) 1997 Todd C. Miller <Todd.Miller@courtesan.com>
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.\" See http://csrc.nist.gov/fips/fip180-1.txt for the detailed standard
.\"
.Dd July 10, 1997
.Dt SHA1 3
.Os
.Sh NAME
.Nm SHA1Init ,
.Nm SHA1Update ,
.Nm SHA1Final ,
.Nm SHA1Transform ,
.Nm SHA1End ,
.Nm SHA1File ,
.Nm SHA1Data
.Nd calculate the NIST Secure Hash Algorithm
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sha1.h>
.Ft void
.Fn SHA1Init "SHA1_CTX *context"
.Ft void
.Fn SHA1Update "SHA1_CTX *context" "const u_char *data" "u_int len"
.Ft void
.Fn SHA1Final "u_char digest[20]" "SHA1_CTX *context"
.Ft void
.Fn SHA1Transform "u_int32_t state[5]" "u_char buffer[64]"
.Ft "char *"
.Fn SHA1End "SHA1_CTX *context" "char *buf"
.Ft "char *"
.Fn SHA1File "char *filename" "char *buf"
.Ft "char *"
.Fn SHA1Data "u_char *data" "u_int len" "char *buf"
.Sh DESCRIPTION
The SHA1 functions implement the NIST Secure Hash Algorithm (SHA-1),
FIPS PUB 180-1.  SHA-1 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 SHA1 functions are considered to be more secure than the
.Xr md4 3
and
.Xr md5 3
functions with which they share a similar interface.
.Pp
The
.Fn SHA1Init
function initializes a SHA1_CTX
.Ar context
for use with
.Fn SHA1Update ,
and
.Fn SHA1Final .
The
.Fn SHA1Update
function adds
.Ar data
of length
.Ar len
to the SHA1_CTX specified by
.Ar context .
.Fn SHA1Final
is called when all data has been added via
.Fn SHA1Update
and stores a message digest in the
.Ar digest
parameter.
When a null pointer is passed to
.Fn SHA1Final
as first argument only the final padding will be applied and the
current context can still be used with
.Fn SHA1Update .
.Pp
The
.Fn SHA1Transform
function is used by
.Fn SHA1Update
to hash 512-bit blocks and forms the core of the algorithm.
Most programs should use the interface provided by
.Fn SHA1Init ,
.Fn SHA1Update
and
.Fn SHA1Final
instead of calling
.Fn SHA1Transform
directly.
.Pp
The
.Fn SHA1End
function is a front end for
.Fn SHA1Final
which converts the digest into an
.Tn ASCII
representation of the 160 bit digest in hexadecimal.
.Pp
The
.Fn SHA1File
function calculates the digest for a file and returns the result via
.Fn SHA1End .
If
.Fn SHA1File
is unable to open the file a NULL pointer is returned.
.Pp
The
.Fn SHA1Data
function
calculates the digest of an arbitrary string and returns the result via
.Fn SHA1End .
.Pp
For each of the
.Fn SHA1End ,
.Fn SHA1File ,
and
.Fn SHA1Data
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 ``0xa9993e36476816aba3e25717850c26c9cd0d89d''.
.Bd -literal -offset indent
SHA1_CTX sha;
u_char results[20];
char *buf;
int n;

buf = "abc";
n = strlen(buf);
SHA1Init(&sha);
SHA1Update(&sha, (u_char *)buf, n);
SHA1Final(results, &sha);

/* Print the digest as one long hex value */
printf("0x");
for (n = 0; n < 20; n++)
	printf("%02x", results[n]);
putchar('\\n');
.Ed
.Pp
Alternately, the helper functions could be used in the following way:
.Bd -literal -offset indent
SHA1_CTX sha;
u_char output[41];
char *buf = "abc";

printf("0x%s\en", SHA1Data(buf, strlen(buf), output));
.Ed
.Sh CAVEATS
This implementation of SHA-1 has not been validated by NIST
and as such is not in official compliance with the standard.
.Pp
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.
.Sh AUTHOR
This implementation of SHA-1 was written by Steve Reid.
.Pp
The
.Fn SHA1End ,
.Fn SHA1File ,
and
.Fn SHA1Data
helper functions are derived from code written by Poul-Henning Kamp.
.Sh SEE ALSO
.Xr sha1 1 ,
.Xr md4 3 ,
.Xr md5 3 ,
.Xr rmd160 3
.Pp
.Rs
.%A J. Burrows
.%T The Secure Hash Standard
.%O FIPS PUB 180-1
.Re
.Sh HISTORY
The SHA-1 functions appeared in
.Ox 2.0 .