hash/sha1/sha1.3

.\"	$NetBSD: sha1.3,v 1.9 2018/11/27 10:38:14 wiz Exp $
.\"	$OpenBSD: sha1.3,v 1.9 1998/03/07 22:18:12 millert Exp $
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.\" Copyright (c) 1997, 2004 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 November 27, 2018
.Dt SHA1 3
.Os
.Sh NAME
.Nm SHA1Init ,
.Nm SHA1Update ,
.Nm SHA1Final ,
.Nm SHA1Transform ,
.Nm SHA1End ,
.Nm SHA1File ,
.Nm SHA1FileChunk ,
.Nm SHA1Data
.Nd calculate the NIST Secure Hash Algorithm
.Sh SYNOPSIS
.In sys/types.h
.In sha1.h
.Ft void
.Fn SHA1Init "SHA1_CTX *context"
.Ft void
.Fn SHA1Update "SHA1_CTX *context" "const uint8_t *data" "u_int len"
.Ft void
.Fn SHA1Final "uint8_t digest[20]" "SHA1_CTX *context"
.Ft void
.Fn SHA1Transform "uint32_t state[5]" "uint8_t buffer[64]"
.Ft "char *"
.Fn SHA1End "SHA1_CTX *context" "char *buf"
.Ft "char *"
.Fn SHA1File "char *filename" "char *buf"
.Ft "char *"
.Fn SHA1FileChunk "const char *filename" "char *buf" "off_t offset" "off_t length"
.Ft "char *"
.Fn SHA1Data "uint8_t *data" "size_t 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
.Fn SHA1FileChunk
behaves like
.Fn SHA1File
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 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;
uint8_t results[20];
char *buf;
int n;

buf = "abc";
n = strlen(buf);
SHA1Init(&sha);
SHA1Update(&sha, (uint8_t *)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('\en');
.Ed
.Pp
Alternately, the helper functions could be used in the following way:
.Bd -literal -offset indent
SHA1_CTX sha;
uint8_t output[41];
char *buf = "abc";

printf("0x%s", SHA1Data(buf, strlen(buf), output));
.Ed
.Sh SEE ALSO
.\"	.Xr sha1 1 ,
.Xr md5 1 ,
.Xr md4 3 ,
.Xr md5 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
.Nx 1.4 .
.Sh AUTHORS
This implementation of SHA-1 was written by
.An Steve Reid .
.Pp
The
.Fn SHA1End ,
.Fn SHA1File ,
.Fn SHA1FileChunk ,
and
.Fn SHA1Data
helper functions are derived from code written by Poul-Henning Kamp.
.Sh BUGS
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.