Tribblix: manual page: sha2.3ext

SHA2(3EXT) Extended Library Functions SHA2(3EXT)

NAME

sha2, SHA2Init, SHA2Update, SHA2Final, SHA256Init, SHA256Update,
SHA256Final, SHA384Init, SHA384Update, SHA384Final, SHA512Init,
SHA512Update, SHA512Final - SHA2 digest functions

SYNOPSIS

cc [ flag ... ] file ... -lmd [ library ... ]
#include <sha2.h>

void SHA2Init(uint64_t mech, SHA2_CTX *context);

void SHA2Update(SHA2_CTX *context, unsigned char *input,
size_t inlen);

void SHA2Final(unsigned char *output, SHA2_CTX *context);

void SHA256Init(SHA256_CTX *context);

void SHA256Update(SHA256_CTX *context, unsigned char *input,
size_t inlen);

void SHA256Final(unsigned char *output, SHA256_CTX *context);

void SHA384Init(SHA384_CTX *context);

void SHA384Update(SHA384_CTX *context, unsigned char *input,
size_t inlen);

void SHA384Final(unsigned char *output, 384_CTX *context);

void SHA512Init(SHA512_CTX *context);

void SHA512Update(SHA512_CTX *context, unsigned char *input,
size_t inlen);

void SHA512Final(unsigned char *output, 512_CTX *context);

DESCRIPTION

The SHA2Init(), SHA2Update(), SHA2Final() functions implement the
SHA256, SHA384, SHA512, SHA512/224 and SHA512/256 message-digest
algorithms. The algorithms take as input a message of arbitrary
length and produce a 200-bit "fingerprint" or "message digest" as
output. The SHA2 message-digest algorithms are intended for digital
signature applications in which large files are "compressed" in a
secure manner before being encrypted with a private (secret) key
under a public-key cryptosystem such as RSA.

SHA2Init(), SHA2Update(), SHA2Final()

The SHA2Init(), SHA2Update(), and SHA2Final() functions allow an
SHA2 digest to be computed over multiple message blocks. Between
blocks, the state of the SHA2 computation is held in an SHA2
context structure allocated by the caller. A complete digest
computation consists of calls to SHA2 functions in the following
order: one call to SHA2Init(), one or more calls to SHA2Update(),
and one call to SHA2Final().

The SHA2Init() function initializes the SHA2 context structure
pointed to by context. The mech argument is one of SHA256,
SHA512, SHA384, SHA512_224, SHA512_256.

The SHA2Update() function computes a partial SHA2 digest on the
inlen-byte message block pointed to by input, and updates the
SHA2 context structure pointed to by context accordingly.

The SHA2Final() function generates the final SHA2Final digest,
using the SHA2 context structure pointed to by context. The SHA2
digest is written to output. After a call to SHA2Final(), the
state of the context structure is undefined. It must be
reinitialized with SHA2Init() before it can be used again.

SHA256Init(), SHA256Update(), SHA256Final(), SHA384Init(),
SHA384Update(), SHA384Final(), SHA512Init(), SHA512Update(),
SHA512Final()

Alternative APIs exist as named above. The Update() and Final()
sets of functions operate exactly as the previously described
SHA2Update() and SHA2Final() functions. The SHA256Init(),
SHA384Init(), and SHA512Init() functions do not take the mech
argument as it is implicit in the function names.

RETURN VALUES

These functions do not return a value.

EXAMPLES

Example 1: Authenticate a message found in multiple buffers

The following is a sample function that authenticates a message found
in multiple buffers. The calling function provides an authentication
buffer to contain the result of the SHA2 digest.

#include <sys/types.h>
#include <sys/uio.h>
#include <sha2.h>

int
AuthenticateMsg(unsigned char *auth_buffer, struct iovec
*messageIov, unsigned int num_buffers)
{
SHA2_CTX sha2_context;
unsigned int i;

SHA2Init(SHA384, &sha2_context);

for(i=0; i<num_buffers; i++)
{
SHA2Update(&sha2_context, messageIov->iov_base,
messageIov->iov_len);
messageIov += sizeof(struct iovec);
}

SHA2Final(auth_buffer, &sha2_context);

return 0;
}

Example 2: Authenticate a message found in multiple buffers

The following is a sample function that authenticates a message found
in multiple buffers. The calling function provides an authentication
buffer that will contain the result of the SHA384 digest, using
alternative interfaces.

int
AuthenticateMsg(unsigned char *auth_buffer, struct iovec
*messageIov, unsigned int num_buffers)
{
SHA384_CTX ctx;
unsigned int i;

SHA384Init(&ctx);

for(i=0, i<num_buffers; i++
{
SHA384Update(&ctx, messageIov->iov_base,
messageIov->iov_len);
messageIov += sizeof(struct iovec);
}

SHA384Final(auth_buffer, &ctx);

return 0;
}

ATTRIBUTES