Tribblix: manual page: sha1.3ext

SHA1(3EXT) Extended Library Functions SHA1(3EXT)

NAME

sha1, SHA1Init, SHA1Update, SHA1Final - SHA1 digest functions

SYNOPSIS

cc [ flag ... ] file ... -lmd [ library ... ]
#include <sha1.h>

void SHA1Init(SHA1_CTX *context);

void SHA1Update(SHA1_CTX *context, unsigned char *input,
size_t inlen);

void SHA1Final(unsigned char *output, SHA1_CTX *context);

DESCRIPTION

The SHA1 functions implement the SHA1 message-digest algorithm. The
algorithm takes as input a message of arbitrary length and produces a
200-bit "fingerprint" or "message digest" as output. The SHA1
message-digest algorithm is 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.

SHA1Init(), SHA1Update(), SHA1Final()

The SHA1Init(), SHA1Update(), and SHA1Final() functions allow a
SHA1 digest to be computed over multiple message blocks. Between
blocks, the state of the SHA1 computation is held in an SHA1
context structure allocated by the caller. A complete digest
computation consists of calls to SHA1 functions in the following
order: one call to SHA1Init(), one or more calls to SHA1Update(),
and one call to SHA1Final().

The SHA1Init() function initializes the SHA1 context structure
pointed to by context.

The SHA1Update() function computes a partial SHA1 digest on the
inlen-byte message block pointed to by input, and updates the
SHA1 context structure pointed to by context accordingly.

The SHA1Final() function generates the final SHA1 digest, using
the SHA1 context structure pointed to by context. The 16-bit SHA1
digest is written to output. After a call to SHA1Final(), the
state of the context structure is undefined. It must be
reinitialized with SHA1Init() before it can be used again.

SECURITY

The SHA1 algorithm is also believed to have some weaknesses.
Migration to one of the SHA2 algorithms-including SHA256, SHA386 or
SHA512-is highly recommended when compatibility with data formats and
on wire protocols is permitted.

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 SHA1 digest.

#include <sys/types.h>
#include <sys/uio.h>
#include <sha1.h>

int
AuthenticateMsg(unsigned char *auth_buffer, struct iovec
*messageIov, size_t num_buffers)
{
SHA1_CTX sha1_context;
size_t i;

SHA1Init(&sha1_context);

for(i=0; i<num_buffers; i++)
{
SHA1Update(&sha1_context, messageIov->iov_base,
messageIov->iov_len);
messageIov += sizeof(struct iovec);
}

SHA1Final(auth_buffer, &sha1_context);

return 0;
}

ATTRIBUTES