SHA1(3)

NAME
SHA1Init, SHA1Update, SHA1Final, SHA1Transform, SHA1End, SHA1File, SHA1Data - calculate the NIST Secure Hash Algorithm

SYNOPSIS
#include <sys/types.h>
#include <sha1.h>
void
SHA1Init(SHA1_CTX *context);
void
SHA1Update(SHA1_CTX *context, const u_char *data, u_int len);
void
SHA1Final(u_char digest[20], SHA1_CTX *context);
void
SHA1Transform(uint32_t state[5], u_char buffer[64]);
char *
SHA1End(SHA1_CTX *context, char *buf);
char *
SHA1File(char *filename, char *buf);
char *
SHA1Data(u_char *data, size_t len, char *buf);

DESCRIPTION
The SHA1 functions implement the NIST Secure Hash Algorithm (SHA-1), FIPS PUB 180-1. SHA-1 is used to generate a condensed representation of a message called a message digest. The algorithm takes a message less than 2^64 bits as input and produces a 160-bit digest suitable for use as a digital signature.

The SHA1 functions are considered to be more secure than the md4(3) and md5(3) functions with which they share a similar interface.

The SHA1Init() function initializes a SHA1_CTX context for use with SHA1Update(), and SHA1Final(). The SHA1Update() function adds data of length len to the SHA1_CTX specified by context. SHA1Final() is called when all data has been added via SHA1Update() and stores a message digest in the digest parameter. When a null pointer is passed to SHA1Final() as first argument only the final padding will be applied and the current context can still be used with SHA1Update().

The SHA1Transform() function is used by SHA1Update() to hash 512-bit blocks and forms the core of the algorithm. Most programs should use the interface provided by SHA1Init(), SHA1Update() and SHA1Final() instead of calling SHA1Transform() directly.

The SHA1End() function is a front end for SHA1Final() which converts the digest into an ASCII representation of the 160 bit digest in hexadecimal.

The SHA1File() function calculates the digest for a file and returns the result via SHA1End(). If SHA1File() is unable to open the file a NULL pointer is returned.

The SHA1Data() function calculates the digest of an arbitrary string and returns the result via SHA1End().

For each of the SHA1End(), SHA1File(), and SHA1Data() functions the buf parameter should either be a string of at least 41 characters in size 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 follow code fragment will calculate the digest for the string "abc" which is ``0xa9993e36476816aba3e25717850c26c9cd0d89d''.

    SHA1_CTX sha;
    u_char results[20];
    char *buf;
    int n;
    buf = "abc";
    n = strlen(buf);
    SHA1Init(sha);
    SHA1Update(sha, (u_char *)buf, n);
    SHA1Final(results, sha);
    /* Print the digest as one long hex value */
    printf("0x");
    for (n = 0; n  20; n++)
    	printf("%02x", results[n]);
    putchar('\n');

Alternately, the helper functions could be used in the following way:

    SHA1_CTX sha;
    u_char output[41];
    char *buf = "abc";
    printf("0x%s", SHA1Data(buf, strlen(buf), output));

SEE ALSO
md5(1), md4(3), md5(3)

J. Burrows, The Secure Hash Standard, FIPS PUB 180-1.

HISTORY
The SHA-1 functions appeared in NetBSD 1.4.

AUTHORS
This implementation of SHA-1 was written by Steve Reid.

The SHA1End(), SHA1File(), and SHA1Data() helper functions are derived from code written by Poul-Henning Kamp.

BUGS
This implementation of SHA-1 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 (ie: an array of five 32-bit integers) it will be necessary to perform byte swapping on little endian machines such as the i386, alpha, and VAX.