man/man3ext/sha2.3ext

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 SHA2 3EXT "Sep 10, 2018"
 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,
 unsigned int inlen);


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


void SHA256Init(SHA256_CTX *context);


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


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


void SHA384Init(SHA384_CTX *context);


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


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


void SHA512Init(SHA512_CTX *context);


void SHA512Update(SHA512_CTX *context, unsigned char *input,
 unsigned int 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

See attributes(5) for descriptions of the following attributes:


ATTRIBUTE TYPE ATTRIBUTE VALUE
Interface Stability Committed
MT-Level MT-Safe


 SEE ALSO

libmd(3LIB)

FIPS 180-2