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,
     unsigned int 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 160-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 SHA224, 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, unsigned int num_buffers)
{
    SHA1_CTX sha1_context;
    unsigned int 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

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

See Also

sha2(3EXT), libmd(3LIB)

RFC 1374