NAME
SHA256_Init,
SHA256_Update,
SHA256_Pad,
SHA256_Final,
SHA256_Transform,
SHA256_End,
SHA256_File,
SHA256_FileChunk,
SHA256_Data —
calculate the NIST
Secure Hash Standard (version 2)
SYNOPSIS
#include <sys/types.h>
#include <sha2.h>
void
SHA224_Init(
SHA224_CTX
*context);
void
SHA224_Update(
SHA224_CTX
*context,
const uint8_t
*data,
size_t len);
void
SHA224_Pad(
SHA224_CTX
*context);
void
SHA224_Final(
uint8_t
digest[SHA224_DIGEST_LENGTH],
SHA224_CTX *context);
void
SHA224_Transform(
uint32_t
state[8],
const uint8_t
buffer[SHA224_BLOCK_LENGTH]);
char *
SHA224_End(
SHA224_CTX
*context,
char *buf);
char *
SHA224_File(
const
char *filename,
char
*buf);
char *
SHA224_FileChunk(
const
char *filename,
char
*buf,
off_t offset,
off_t length);
char *
SHA224_Data(
uint8_t
*data,
size_t len,
char *buf);
void
SHA256_Init(
SHA256_CTX
*context);
void
SHA256_Update(
SHA256_CTX
*context,
const uint8_t
*data,
size_t len);
void
SHA256_Pad(
SHA256_CTX
*context);
void
SHA256_Final(
uint8_t
digest[SHA256_DIGEST_LENGTH],
SHA256_CTX *context);
void
SHA256_Transform(
uint32_t
state[8],
const uint8_t
buffer[SHA256_BLOCK_LENGTH]);
char *
SHA256_End(
SHA256_CTX
*context,
char *buf);
char *
SHA256_File(
const
char *filename,
char
*buf);
char *
SHA256_FileChunk(
const
char *filename,
char
*buf,
off_t offset,
off_t length);
char *
SHA256_Data(
uint8_t
*data,
size_t len,
char *buf);
void
SHA384_Init(
SHA384_CTX
*context);
void
SHA384_Update(
SHA384_CTX
*context,
const uint8_t
*data,
size_t len);
void
SHA384_Pad(
SHA384_CTX
*context);
void
SHA384_Final(
uint8_t
digest[SHA384_DIGEST_LENGTH],
SHA384_CTX *context);
void
SHA384_Transform(
uint64_t
state[8],
const uint8_t
buffer[SHA384_BLOCK_LENGTH]);
char *
SHA384_End(
SHA384_CTX
*context,
char *buf);
char *
SHA384_File(
char
*filename,
char
*buf);
char *
SHA384_FileChunk(
char
*filename,
char *buf,
off_t offset,
off_t length);
char *
SHA384_Data(
uint8_t
*data,
size_t len,
char *buf);
void
SHA512_Init(
SHA512_CTX
*context);
void
SHA512_Update(
SHA512_CTX
*context,
const uint8_t
*data,
size_t len);
void
SHA512_Pad(
SHA512_CTX
*context);
void
SHA512_Final(
uint8_t
digest[SHA512_DIGEST_LENGTH],
SHA512_CTX *context);
void
SHA512_Transform(
uint64_t
state[8],
const uint8_t
buffer[SHA512_BLOCK_LENGTH]);
char *
SHA512_End(
SHA512_CTX
*context,
char *buf);
char *
SHA512_File(
char
*filename,
char
*buf);
char *
SHA512_FileChunk(
char
*filename,
char *buf,
off_t offset,
off_t length);
char *
SHA512_Data(
uint8_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
four families of functions, with names corresponding to the number of bits in
the resulting message digest. The SHA-224 and 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 224, 256, 384, and 512-bit versions of SHA2
share the same interface. For brevity, only the 256-bit variants are described
below.
The
SHA256_Init() function initializes a SHA256_CTX
context for use with
SHA256_Update(),
and
SHA256_Final(). The
SHA256_Update()
function adds
data of length
len
to the SHA256_CTX specified by
context.
SHA256_Final() is called when all data has been added via
SHA256_Update() and stores a message digest in the
digest parameter.
The
SHA256_Pad() function can be used to apply padding to the
message digest as in
SHA256_Final(), but the current context
can still be used with
SHA256_Update().
The
SHA256_Transform() function is used by
SHA256_Update() to hash 512-bit blocks and forms the core of
the algorithm. Most programs should use the interface provided by
SHA256_Init(),
SHA256_Update(), and
SHA256_Final() instead of calling
SHA256_Transform() directly.
The
SHA256_End() function is a front end for
SHA256_Final() which converts the digest into an ASCII
representation of the digest in hexadecimal.
The
SHA256_File() function calculates the digest for a file
and returns the result via
SHA256_End(). If
SHA256_File() is unable to open the file, a
NULL
pointer is returned.
SHA256_FileChunk() behaves like
SHA256_File() 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
SHA256_Data() function calculates the digest of an
arbitrary string and returns the result via
SHA256_End().
For each of the
SHA256_End(),
SHA256_File(),
SHA256_FileChunk(), and
SHA256_Data()
functions the
buf parameter should either be a string
large enough to hold the resulting digest (e.g.,
SHA224_DIGEST_STRING_LENGTH
,
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”.
SHA256_CTX ctx;
uint8_t results[SHA256_DIGEST_LENGTH];
char *buf;
int n;
buf = "abc";
n = strlen(buf);
SHA256_Init(&ctx);
SHA256_Update(&ctx, (uint8_t *)buf, n);
SHA256_Final(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:
SHA256_CTX ctx;
uint8_t output[SHA256_DIGEST_STRING_LENGTH];
char *buf = "abc";
printf("0x%s\n", SHA256_Data(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 and
NetBSD 3.0.
AUTHORS
This implementation of the SHA functions was written by Aaron D. Gifford.
The
SHA256_End(),
SHA256_File(),
SHA256_FileChunk(), and
SHA256_Data()
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 five
32-bit integers) it will be necessary to perform byte swapping on little
endian machines such as the i386, alpha, and vax.