.\"	$OpenBSD: sha2.3,v 1.15 2008/09/06 12:00:19 djm Exp $
.\"
.\" Copyright (c) 2003, 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.
.\"
.\" Sponsored in part by the Defense Advanced Research Projects
.\" Agency (DARPA) and Air Force Research Laboratory, Air Force
.\" Materiel Command, USAF, under agreement number F39502-99-1-0512.
.\"
.\" See http://www.nist.gov/sha/ for the detailed standard
.\"
.Dd $Mdocdate: September 12 2008 $
.Dt SHA2 3
.Os
.Sh NAME
.Nm SHA256Init ,
.Nm SHA256Update ,
.Nm SHA256Pad ,
.Nm SHA256Final ,
.Nm SHA256Transform ,
.Nm SHA256End ,
.Nm SHA256File ,
.Nm SHA256FileChunk ,
.Nm SHA256Data
.Nd calculate the NIST Secure Hash Standard (version 2)
.Sh LIBRARY
.Lb libmd
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sha2.h>
.Ft void
.Fn SHA256Init "SHA2_CTX *context"
.Ft void
.Fn SHA256Update "SHA2_CTX *context" "const uint8_t *data" "size_t len"
.Ft void
.Fn SHA256Pad "SHA2_CTX *context"
.Ft void
.Fn SHA256Final "uint8_t digest[SHA256_DIGEST_LENGTH]" "SHA2_CTX *context"
.Ft void
.Fn SHA256Transform "uint32_t state[8]" "const uint8_t buffer[SHA256_BLOCK_LENGTH]"
.Ft "char *"
.Fn SHA256End "SHA2_CTX *context" "char *buf"
.Ft "char *"
.Fn SHA256File "const char *filename" "char *buf"
.Ft "char *"
.Fn SHA256FileChunk "const char *filename" "char *buf" "off_t offset" "off_t length"
.Ft "char *"
.Fn SHA256Data "uint8_t *data" "size_t len" "char *buf"
.Ft void
.Fn SHA384Init "SHA2_CTX *context"
.Ft void
.Fn SHA384Update "SHA2_CTX *context" "const uint8_t *data" "size_t len"
.Ft void
.Fn SHA384Pad "SHA2_CTX *context"
.Ft void
.Fn SHA384Final "uint8_t digest[SHA384_DIGEST_LENGTH]" "SHA2_CTX *context"
.Ft void
.Fn SHA384Transform "uint64_t state[8]" "const uint8_t buffer[SHA384_BLOCK_LENGTH]"
.Ft "char *"
.Fn SHA384End "SHA2_CTX *context" "char *buf"
.Ft "char *"
.Fn SHA384File "char *filename" "char *buf"
.Ft "char *"
.Fn SHA384FileChunk "char *filename" "char *buf" "off_t offset" "off_t length"
.Ft "char *"
.Fn SHA384Data "uint8_t *data" "size_t len" "char *buf"
.Ft void
.Fn SHA512Init "SHA2_CTX *context"
.Ft void
.Fn SHA512Update "SHA2_CTX *context" "const uint8_t *data" "size_t len"
.Ft void
.Fn SHA512Pad "SHA2_CTX *context"
.Ft void
.Fn SHA512Final "uint8_t digest[SHA512_DIGEST_LENGTH]" "SHA2_CTX *context"
.Ft void
.Fn SHA512Transform "uint64_t state[8]" "const uint8_t buffer[SHA512_BLOCK_LENGTH]"
.Ft "char *"
.Fn SHA512End "SHA2_CTX *context" "char *buf"
.Ft "char *"
.Fn SHA512File "char *filename" "char *buf"
.Ft "char *"
.Fn SHA512FileChunk "char *filename" "char *buf" "off_t offset" "off_t length"
.Ft "char *"
.Fn SHA512Data "uint8_t *data" "size_t len" "char *buf"
.Sh DESCRIPTION
The SHA2 functions implement the NIST Secure Hash Standard,
FIPS PUB 180-2.
The SHA2 functions are used to generate a condensed representation of a
message called a message digest, suitable for use as a digital signature.
There are three families of functions, with names corresponding to
the number of bits in the resulting message digest.
The SHA-256 functions are limited to processing a message of less
than 2^64 bits as input.
The SHA-384 and SHA-512 functions can process a message of at most 2^128 - 1
bits as input.
.Pp
The SHA2 functions are considered to be more secure than the
.Xr sha1 3
functions with which they share a similar interface.
The 256, 384, and 512-bit versions of SHA2 share the same interface.
For brevity, only the 256-bit variants are described below.
.Pp
The
.Fn SHA256Init
function initializes a SHA2_CTX
.Ar context
for use with
.Fn SHA256Update
and
.Fn SHA256Final .
The
.Fn SHA256Update
function adds
.Ar data
of length
.Ar len
to the SHA2_CTX specified by
.Ar context .
.Fn SHA256Final
is called when all data has been added via
.Fn SHA256Update
and stores a message digest in the
.Ar digest
parameter.
.Pp
The
.Fn SHA256Pad
function can be used to apply padding to the message digest as in
.Fn SHA256Final ,
but the current context can still be used with
.Fn SHA256Update .
.Pp
The
.Fn SHA256Transform
function is used by
.Fn SHA256Update
to hash 512-bit blocks and forms the core of the algorithm.
Most programs should use the interface provided by
.Fn SHA256Init ,
.Fn SHA256Update ,
and
.Fn SHA256Final
instead of calling
.Fn SHA256Transform
directly.
.Pp
The
.Fn SHA256End
function is a front end for
.Fn SHA256Final
which converts the digest into an
.Tn ASCII
representation of the digest in hexadecimal.
.Pp
The
.Fn SHA256File
function calculates the digest for a file and returns the result via
.Fn SHA256End .
If
.Fn SHA256File
is unable to open the file, a
.Dv NULL
pointer is returned.
.Pp
.Fn SHA256FileChunk
behaves like
.Fn SHA256File
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 SHA256Data
function
calculates the digest of an arbitrary string and returns the result via
.Fn SHA256End .
.Pp
For each of the
.Fn SHA256End ,
.Fn SHA256File ,
.Fn SHA256FileChunk ,
and
.Fn SHA256Data
functions the
.Ar buf
parameter should either be a string large enough to hold the resulting digest
(e.g.\&
.Ev SHA256_DIGEST_STRING_LENGTH ,
.Ev SHA384_DIGEST_STRING_LENGTH ,
or
.Ev SHA512_DIGEST_STRING_LENGTH ,
depending on the function being used)
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 following code fragment will calculate the SHA-256 digest for the string
.Qq abc ,
which is
.Dq 0xba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad .
.Bd -literal -offset indent
SHA2_CTX ctx;
uint8_t results[SHA256_DIGEST_LENGTH];
char *buf;
int n;

buf = "abc";
n = strlen(buf);
SHA256Init(&ctx);
SHA256Update(&ctx, (uint8_t *)buf, n);
SHA256Final(results, &ctx);

/* Print the digest as one long hex value */
printf("0x");
for (n = 0; n \*(Lt SHA256_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
uint8_t output[SHA256_DIGEST_STRING_LENGTH];
char *buf = "abc";

printf("0x%s\en", SHA256Data(buf, strlen(buf), output));
.Ed
.Sh SEE ALSO
.Xr cksum 1 ,
.Xr md4 3 ,
.Xr md5 3 ,
.Xr rmd160 3 ,
.Xr sha1 3
.Rs
.%T Secure Hash Standard
.%O FIPS PUB 180-2
.Re
.Sh HISTORY
The SHA2 functions appeared in
.Ox 3.4 .
.Sh AUTHORS
This implementation of the SHA functions was written by Aaron D. Gifford.
.Pp
The
.Fn SHA256End ,
.Fn SHA256File ,
.Fn SHA256FileChunk ,
and
.Fn SHA256Data
helper functions are derived from code written by Poul-Henning Kamp.
.Sh CAVEATS
This implementation of the Secure Hash Standard 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 (i.e.\&
an array of 32-bit integers) it will be necessary to
perform byte swapping on little endian machines such as the i386, alpha,
and vax.