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.