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.

Debian                                          February 13, 2008                                        SHA1(3)