|SHA1(3)||Library Functions Manual||SHA1(3)|
— calculate the NIST Secure Hash
Message Digest (MD4, MD5, etc.) Support Library (libmd, -lmd)
*context, const uint8_t
state, const uint8_t
char *filename, char
char *filename, char
*buf, off_t offset,
uint8_t *data, size_t
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.
While the SHA1 functions are considered to be more secure than the md4(3) and md5(3) functions with which they share a similar interface, they are considered insecure as of 2005, and as of 2020 chosen-prefix attacks have become practical, thus these must not be used in cryptographic contexts.
function initializes a SHA1_CTX context for use with
SHA1Update() function adds
data of length len to the
SHA1_CTX specified by context.
SHA1Final() is called when all data has been added
SHA1Update() and stores a message digest in the
function is used by
to hash 512-bit blocks and forms the core of the algorithm. Most programs
should use the interface provided by
instead of calling
function calculates the digest for a file and returns the result via
unable to open the file a NULL pointer is returned.
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
function calculates the digest of an arbitrary string and returns the result
For each of the
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
The follow code fragment will calculate the digest for the string "abc" which is ``0xa9993e364706816aba3e25717850c26c9cd0d89d''.
SHA1_CTX sha; uint8_t results[SHA1_DIGEST_LENGTH]; char *buf; int n; buf = "abc"; n = strlen(buf); SHA1Init(&sha); SHA1Update(&sha, (uint8_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:
uint8_t output[SHA1_DIGEST_STRING_LENGTH]; char *buf = "abc"; printf("0x%s\n", SHA1Data(buf, strlen(buf), output));
J. Burrows, The Secure Hash Standard, FIPS PUB 180-1.
D. Eastlake and P. Jones, US Secure Hash Algorithm 1, RFC 3174.
The SHA-1 functions appeared in OpenBSD 2.0.
This implementation of SHA-1 was written by Steve Reid.
SHA1Data() helper functions are derived from
code written by Poul-Henning Kamp.
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.
|February 13, 2008||Debian|