SHA2
Section: C Library Functions (3)
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NAME
SHA256Init
SHA256Update
SHA256Pad
SHA256Final
SHA256Transform
SHA256End
SHA256File
SHA256FileChunk
SHA256Data
- calculate the NIST Secure Hash Standard (version 2)
LIBRARY
Lb libmd
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
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
Fn SHA256Init
function initializes a SHA2_CTX
context
for use with
Fn SHA256Update
and
Fn SHA256Final .
The
Fn SHA256Update
function adds
data
of length
len
to the SHA2_CTX specified by
context
Fn SHA256Final
is called when all data has been added via
Fn SHA256Update
and stores a message digest in the
digest
parameter.
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 .
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.
The
Fn SHA256End
function is a front end for
Fn SHA256Final
which converts the digest into an
ASCII
representation of the digest in hexadecimal.
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
NULL
pointer is returned.
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.
The
Fn SHA256Data
function
calculates the digest of an arbitrary string and returns the result via
Fn SHA256End .
For each of the
Fn SHA256End ,
Fn SHA256File ,
Fn SHA256FileChunk ,
and
Fn 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
Qq abc ,
which is
``0xba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad''
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 < SHA256_DIGEST_LENGTH; n++)
printf("%02x", results[n]);
putchar('\n');
Alternately, the helper functions could be used in the following way:
uint8_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
Ox 3.4 .
AUTHORS
This implementation of the SHA functions was written by Aaron D. Gifford.
The
Fn SHA256End ,
Fn SHA256File ,
Fn SHA256FileChunk ,
and
Fn 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.
Index
- NAME
-
- LIBRARY
-
- SYNOPSIS
-
- DESCRIPTION
-
- EXAMPLES
-
- SEE ALSO
-
- HISTORY
-
- AUTHORS
-
- CAVEATS
-
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Time: 07:34:35 GMT, May 09, 2024