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)
#include <sys/types.h>
#include <sha2.h>
void
SHA256_Init(SHA256_CTX *context);
void
SHA256_Update(SHA256_CTX *context, const u_int8_t *data,
size_t len);
void
SHA256_Pad(SHA256_CTX *context);
void
SHA256_Final(u_int8_t digest[SHA256_DIGEST_LENGTH],
SHA256_CTX *context);
void
SHA256_Transform(u_int32_t state[8],
const u_int8_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(u_int8_t *data, size_t len, char *buf);
void
SHA384_Init(SHA384_CTX *context);
void
SHA384_Update(SHA384_CTX *context, const u_int8_t *data,
size_t len);
void
SHA384_Pad(SHA384_CTX *context);
void
SHA384_Final(u_int8_t digest[SHA384_DIGEST_LENGTH],
SHA384_CTX *context);
void
SHA384_Transform(u_int64_t state[8],
const u_int8_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(u_int8_t *data, size_t len, char *buf);
void
SHA512_Init(SHA512_CTX *context);
void
SHA512_Update(SHA512_CTX *context, const u_int8_t *data,
size_t len);
void
SHA512_Pad(SHA512_CTX *context);
void
SHA512_Final(u_int8_t digest[SHA512_DIGEST_LENGTH],
SHA512_CTX *context);
void
SHA512_Transform(u_int64_t state[8],
const u_int8_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(u_int8_t *data, size_t len, char *buf);
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 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. 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.
The following code fragment will calculate the SHA-256 digest for the
string "abc", which is
``0xba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad''.
SHA256_CTX ctx;
u_int8_t results[SHA256_DIGEST_LENGTH];
char *buf;
int n;
buf = "abc";
n = strlen(buf);
SHA256_Init(&ctx);
SHA256_Update(&ctx, (u_int8_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('0);
Alternately, the helper functions could be used in the following way:
SHA256_CTX ctx;
u_int8_t output[SHA256_DIGEST_STRING_LENGTH];
char *buf = "abc";
printf("0x%s0, SHA256_Data(buf, strlen(buf), output));
cksum(1), md4(3), md5(3), rmd160(3), sha1(3)
Secure Hash Standard, FIPS PUB 180-2.
The SHA2 functions appeared in OpenBSD 3.4.
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.
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
(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.
OpenBSD 3.6 April 24, 2003
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