NAME
SHA1Init,
SHA1Update, SHA1Pad,
SHA1Final, SHA1Transform,
SHA1End, SHA1File,
SHA1FileChunk, 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_int8_t
*data, size_t
len);
void
SHA1Pad(SHA1_CTX
*context);
void
SHA1Final(u_int8_t
digest[SHA1_DIGEST_LENGTH],
SHA1_CTX *context);
void
SHA1Transform(u_int32_t
state[5], const u_int8_t
buffer[SHA1_BLOCK_LENGTH]);
char *
SHA1End(SHA1_CTX
*context, char
*buf);
char *
SHA1File(const
char *filename, char
*buf);
char *
SHA1FileChunk(const
char *filename, char
*buf, off_t offset,
off_t length);
char *
SHA1Data(const
u_int8_t *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.
SHA-1 has been broken; it should only be used where necessary for backward compatibility. The attack on SHA-1 is in the nature of finding “collisions” — that is, multiple inputs which hash to the same value. It is still unlikely for an attacker to be able to determine the exact original input given a hash value.
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.
The
SHA1Pad()
function can be used to apply padding to the message digest as in
SHA1Final(),
but 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.
SHA1FileChunk()
behaves like SHA1File() but calculates the digest
only for that portion of the file starting at offset
and continuing for length bytes or until end of file
is reached, whichever comes first. A zero length can
be specified to read until end of file. A negative
length or offset will be
ignored.
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 following code fragment will calculate the digest for the string "abc" which is “0xa9993e364706816aba3e25717850c26c9cd0d89d”.
SHA1_CTX sha;
u_int8_t results[SHA1_DIGEST_LENGTH];
char *buf;
int n;
buf = "abc";
n = strlen(buf);
SHA1Init(&sha);
SHA1Update(&sha, (u_int8_t *)buf, n);
SHA1Final(results, &sha);
/* Print the digest as one long hex value */
printf("0x");
for (n = 0; n < SHA1_DIGEST_LENGTH; n++)
printf("%02x", results[n]);
putchar('\n');
Alternately, the helper functions could be used in the following way:
u_int8_t output[SHA1_DIGEST_STRING_LENGTH];
char *buf = "abc";
printf("0x%s\n", SHA1Data(buf, strlen(buf), output));
SEE ALSO
STANDARDS
J. Burrows, The Secure Hash Standard, FIPS PUB 180-1.
D. Eastlake and P. Jones, US Secure Hash Algorithm 1 (SHA1), RFC 3174, September 2001.
HISTORY
The SHA-1 functions appeared in OpenBSD 2.0.
AUTHORS
This implementation of SHA-1 was written by Steve Reid.
The SHA1End(),
SHA1File(), SHA1FileChunk(),
and SHA1Data() helper functions are derived from
code written by Poul-Henning Kamp.