SECHASH(2)                                             SECHASH(2)

     NAME
          md4, md5, ripemd160, sha1, sha2_224, sha2_256, sha2_384,
          sha2_512, hmac_x, hmac_md5, hmac_sha1, hmac_sha2_224,
          hmac_sha2_256, hmac_sha2_384, hmac_sha2_512, poly1305 -
          cryptographically secure hashes

     SYNOPSIS
          #include <u.h>
          #include <libc.h>
          #include <mp.h>
          #include <libsec.h>
          #define DS DigestState /* only to abbreviate SYNOPSIS */

          DS* md4(uchar *data, ulong dlen, uchar *digest, DS *state)

          DS* md5(uchar *data, ulong dlen, uchar *digest, DS *state)

          DS* ripemd160(uchar *data, ulong dlen, uchar *digest, DS
                *state)

          DS* sha1(uchar *data, ulong dlen, uchar *digest, DS *state)

          DS* sha2_224(uchar *data, ulong dlen, uchar *digest, DS
                *state)

          DS* sha2_256(uchar *data, ulong dlen, uchar *digest, DS
                *state)

          DS* sha2_384(uchar *data, ulong dlen, uchar *digest, DS
                *state)

          DS* sha2_512(uchar *data, ulong dlen, uchar *digest, DS
                *state)

          DS* hmac_x(uchar *p, ulong len, uchar *key, ulong klen,
                uchar *digest, DS *s, DS*(*x)(uchar*, ulong, uchar*,
                DS*), int xlen)

          DS* hmac_md5(uchar *data, ulong dlen, uchar *key, ulong
                klen, uchar *digest, DS *state)

          DS* hmac_sha1(uchar *data, ulong dlen, uchar *key, ulong
                klen, uchar *digest, DS *state)

          DS* hmac_sha2_224(uchar *data, ulong dlen, uchar *key, ulong
                klen, uchar *digest, DS *state)

          DS* hmac_sha2_256(uchar *data, ulong dlen, uchar *key, ulong
                klen, uchar *digest, DS *state)

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     SECHASH(2)                                             SECHASH(2)

          DS* hmac_sha2_384(uchar *data, ulong dlen, uchar *key, ulong
                klen, uchar *digest, DS *state)

          DS* hmac_sha2_512(uchar *data, ulong dlen, uchar *key, ulong
                klen, uchar *digest, DS *state)

          DS* poly1305(uchar *p, ulong len, uchar *key, ulong klen,
                uchar *digest, DS *state)

     DESCRIPTION
          The output of a hash is called a digest. A hash is secure
          if, given the hashed data and the digest, it is difficult to
          predict the change to the digest resulting from some change
          to the data without rehashing the whole data.  Therefore, if
          a secret is part of the hashed data, the digest can be used
          as an integrity check of the data by anyone possessing the
          secret.

          The routines md4, md5, ripemd160, sha1, sha2_224, sha2_256,
          sha2_384, sha2_512, differ only in the length of the result-
          ing digest and in the security of the hash.  Sha2_* and
          hmac_sha2_* are the SHA-2 functions; the number after the
          final underscore is the number of bits in the resulting
          digest.  Usage for each is the same.  The first call to the
          routine should have nil as the state parameter.  This call
          returns a state which can be used to chain subsequent calls.
          The last call should have digest non-`nil'.  Digest must
          point to a buffer of at least the size of the digest pro-
          duced.  This last call will free the state and copy the
          result into digest.

          The constants MD4dlen, MD5dlen, RIPEMD160dlen, SHA1dlen,
          SHA2_224dlen, SHA2_256dlen, SHA2_384dlen, SHA2_512dlen and
          Poly1305dlen define the lengths of the digests.

          Hmac_md5, hmac_sha1, hmac_sha2_224, hmac_sha2_256,
          hmac_sha2_384, hmac_sha2_512 and poly1305 are used slightly
          differently.  These hash algorithms are keyed and require a
          key to be specified on every call.  The digest lengths for
          these hashes are the obvious ones from the above list of
          length constants.  The hmac_* routines all call hmac_x
          internally, but hmac_x is not intended for general use.

          Poly1305 is a one-time authenticator designed by D. J. Bern-
          stein is documented in RFC8439. It takes a 32-byte one-time
          key and a message and produces a 16-byte tag.

     EXAMPLES
          To hash a single buffer using md5:

               uchar digest[MD5dlen];

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     SECHASH(2)                                             SECHASH(2)

               md5(data, len, digest, nil);

          To chain a number of buffers together, bounded on each end
          by some secret:

               char buf[256];
               uchar digest[MD5dlen];
               DigestState *s;

               s = md5("my password", 11, nil, nil);
               while((n = read(fd, buf, 256)) > 0)
                    md5(buf, n, nil, s);
               md5("drowssap ym", 11, digest, s);

     SOURCE
          /sys/src/libsec

     SEE ALSO
          blowfish(2), des(2), elgamal(2), rc4(2), rsa(2)
          /lib/rfc/rfc2104  HMAC specification

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