SHA1(3) BSD Programmer's Manual SHA1(3)NAME
SHA1Init, SHA1Update, SHA1Pad, SHA1Final, SHA1Transform, SHA1End,
SHA1File, SHA1FileChunk, SHA1Data - calculate the NIST Secure Hash Algo-
rithm
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 mes-
sage 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.
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 follow code fragment will calculate the digest for the string "abc"
which is ``0xa9993e36476816aba3e25717850c26c9cd0d89d''.
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:
SHA1_CTX sha;
u_int8_t output[SHA1_DIGEST_STRING_LENGTH];
char *buf = "abc";
printf("0x%s\n", SHA1Data(buf, strlen(buf), output));
SEE ALSOcksum(1), sha1(1), adler32(3), md4(3), md5(3), rmd160(3), sfv(3),
sha2(3), suma(3), tiger(3), whirlpool(3)
J. Burrows, The Secure Hash Standard, FIPS PUB 180-1.
D. Eastlake and P. Jones, US Secure Hash Algorithm 1, RFC 3174.
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 func-
tions are derived from code written by Poul-Henning Kamp.
CAVEATS
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.
MirOS BSD #10-current November 22, 2009 2
