NAME
SHA256Init
,
SHA256Update
, SHA256Pad
,
SHA256Final
,
SHA256Transform
, SHA256End
,
SHA256File
, SHA256FileChunk
,
SHA256Data
—
calculate the NIST Secure Hash Standard
(version 2)
SYNOPSIS
#include
<sys/types.h>
#include <sha2.h>
void
SHA256Init
(SHA2_CTX
*context);
void
SHA256Update
(SHA2_CTX
*context, const u_int8_t
*data, size_t
len);
void
SHA256Pad
(SHA2_CTX
*context);
void
SHA256Final
(u_int8_t
digest[SHA256_DIGEST_LENGTH],
SHA2_CTX *context);
void
SHA256Transform
(u_int32_t
state[8], const u_int8_t
buffer[SHA256_BLOCK_LENGTH]);
char *
SHA256End
(SHA2_CTX
*context, char
*buf);
char *
SHA256File
(const
char *filename, char
*buf);
char *
SHA256FileChunk
(const
char *filename, char
*buf, off_t offset,
off_t length);
char *
SHA256Data
(const
u_int8_t *data, size_t
len, char
*buf);
void
SHA384Init
(SHA2_CTX
*context);
void
SHA384Update
(SHA2_CTX
*context, const u_int8_t
*data, size_t
len);
void
SHA384Pad
(SHA2_CTX
*context);
void
SHA384Final
(u_int8_t
digest[SHA384_DIGEST_LENGTH],
SHA2_CTX *context);
void
SHA384Transform
(u_int64_t
state[8], const u_int8_t
buffer[SHA384_BLOCK_LENGTH]);
char *
SHA384End
(SHA2_CTX
*context, char
*buf);
char *
SHA384File
(const
char *filename, char
*buf);
char *
SHA384FileChunk
(const
char *filename, char
*buf, off_t offset,
off_t length);
char *
SHA384Data
(const
u_int8_t *data, size_t
len, char
*buf);
void
SHA512Init
(SHA2_CTX
*context);
void
SHA512Update
(SHA2_CTX
*context, const u_int8_t
*data, size_t
len);
void
SHA512Pad
(SHA2_CTX
*context);
void
SHA512Final
(u_int8_t
digest[SHA512_DIGEST_LENGTH],
SHA2_CTX *context);
void
SHA512Transform
(u_int64_t
state[8], const u_int8_t
buffer[SHA512_BLOCK_LENGTH]);
char *
SHA512End
(SHA2_CTX
*context, char
*buf);
char *
SHA512File
(const
char *filename, char
*buf);
char *
SHA512FileChunk
(const
char *filename, char
*buf, off_t offset,
off_t length);
char *
SHA512Data
(const
u_int8_t *data, size_t
len, char
*buf);
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.
The SHA2 functions are considered to be more secure than the 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.
The
SHA256Init
()
function initializes a SHA2_CTX context for use with
SHA256Update
()
and SHA256Final
(). The
SHA256Update
() function adds
data of length len to the
SHA2_CTX specified by context.
SHA256Final
() is called when all data has been added
via SHA256Update
() and stores a message digest in
the digest parameter.
The
SHA256Pad
()
function can be used to apply padding to the message digest as in
SHA256Final
(),
but the current context can still be used with
SHA256Update
().
The
SHA256Transform
()
function is used by
SHA256Update
()
to hash 512-bit blocks and forms the core of the algorithm. Most programs
should use the interface provided by SHA256Init
(),
SHA256Update
(), and
SHA256Final
() instead of calling
SHA256Transform
() directly.
The
SHA256End
()
function is a front end for
SHA256Final
()
which converts the digest into an ASCII representation of the digest in
hexadecimal.
The
SHA256File
()
function calculates the digest for a file and returns the result via
SHA256End
(). If SHA256File
()
is unable to open the file, a NULL
pointer is
returned.
SHA256FileChunk
()
behaves like SHA256File
() but calculates the digest
only for that portion of the file starting at offset
and continuing for length bytes or until end of file
is reached, whichever comes first. A zero length can
be specified to read until end of file. A negative
length or offset will be
ignored.
The
SHA256Data
()
function calculates the digest of an arbitrary string and returns the result
via SHA256End
().
For each of the
SHA256End
(),
SHA256File
(),
SHA256FileChunk
(), and
SHA256Data
() functions the buf
parameter should either be a string large enough to hold the resulting
digest (e.g. SHA256_DIGEST_STRING_LENGTH
,
SHA384_DIGEST_STRING_LENGTH
, or
SHA512_DIGEST_STRING_LENGTH
, depending on the
function being used) or a NULL
pointer. In the
latter case, space will be dynamically allocated via
malloc(3) and should be freed using
free(3) when it is no longer needed.
EXAMPLES
The following code fragment will calculate the SHA-256 digest for the string "abc", which is “0xba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad”.
SHA2_CTX ctx; u_int8_t results[SHA256_DIGEST_LENGTH]; char *buf; int n; buf = "abc"; n = strlen(buf); SHA256Init(&ctx); SHA256Update(&ctx, (u_int8_t *)buf, n); SHA256Final(results, &ctx); /* Print the digest as one long hex value */ printf("0x"); for (n = 0; n < SHA256_DIGEST_LENGTH; n++) printf("%02x", results[n]); putchar('\n');
Alternately, the helper functions could be used in the following way:
u_int8_t output[SHA256_DIGEST_STRING_LENGTH]; char *buf = "abc"; printf("0x%s\n", SHA256Data(buf, strlen(buf), output));
SEE ALSO
cksum(1), md4(3), md5(3), rmd160(3), sha1(3)
Secure Hash Standard, FIPS PUB 180-2.
HISTORY
The SHA2 functions appeared in OpenBSD 3.4.
AUTHORS
This implementation of the SHA functions was written by Aaron D. Gifford.
The SHA256End
(),
SHA256File
(),
SHA256FileChunk
(), and
SHA256Data
() helper functions are derived from code
written by Poul-Henning Kamp.
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.
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.