SECHASH(3)                                             SECHASH(3)

     NAME
          md4, md5, sha1, hmac_md5, hmac_sha1, md5pickle, md5unpickle,
          sha1pickle, sha1unpickle - cryptographically secure hashes

     SYNOPSIS
          #include <u.h>
          #include <libc.h>
          #include <mp.h>
          #include <libsec.h>

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

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

          char*          md5pickle(MD5state *state)

          MD5state*      md5unpickle(char *p);

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

          char*          sha1pickle(MD5state *state)

          MD5state*      sha1unpickle(char *p);

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

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

     DESCRIPTION
          These functions implement the cryptographic hash functions
          MD4, MD5, and SHA1.  The output of the 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, sha1, hmac_md5, and hmac_sha1 differ
          only in the length of the resulting digest and in the secu-
          rity of the hash.  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

     SECHASH(3)                                             SECHASH(3)

          subsequent calls.  The last call should have digest non-nil.
          Digest must point to a buffer of at least the size of the
          digest produced.  This last call will free the state and
          copy the result into digest. For example, to hash a single
          buffer using md5:

               uchar digest[MD5dlen];

               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);

          The constants MD4dlen, MD5dlen, and SHA1dlen define the
          lengths of the digests.

          Hmac_md5 and hmac_sha1 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
          MD5dlen and SHA1dlen respectively.

          The functions md5pickle and sha1pickle marshal the state of
          a digest for transmission.  Md5unpickle and sha1unpickle
          unmarshal a pickled digest.  All four routines return a
          pointer to a newly malloc(3)'d object.

     SOURCE
          /src/libsec

     SEE ALSO
          aes(3), blowfish(3), des(3), elgamal(3), rc4(3), rsa(3)