SHA1(3)                    Library Functions Manual                    SHA1(3)

NAME
     SHA1Init, SHA1Update, SHA1Pad, SHA1Final, SHA1Transform, SHA1End,
     SHA1File, SHA1FileChunk, SHA1Data - calculate the NIST Secure Hash
     Algorithm

LIBRARY
     Message Digest (MD4, MD5, etc.) Support Library (libmd, -lmd)

SYNOPSIS
     #include <sys/types.h>
     #include <sha1.h>

     void
     SHA1Init(SHA1_CTX *context);

     void
     SHA1Update(SHA1_CTX *context, const uint8_t *data, size_t len);

     void
     SHA1Pad(SHA1_CTX *context);

     void
     SHA1Final(uint8_t digest[SHA1_DIGEST_LENGTH], SHA1_CTX *context);

     void
     SHA1Transform(uint32_t state[5],
         const uint8_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 uint8_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.

     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.

     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 ``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));

SEE ALSO
     cksum(1), sha1(1), md4(3), md5(3), rmd160(3), sha2(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
     functions 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.

Linux 6.10.10-arch1-1          February 13, 2008         Linux 6.10.10-arch1-1