LIBKECCAK_UPDATE(3)        Library Functions Manual        LIBKECCAK_UPDATE(3)

NAME
       libkeccak_update - Partially hash a message with erasure

SYNOPSIS
       #include <libkeccak.h>

       int libkeccak_update(struct libkeccak_state *state, const void *msg, size_t msglen);

       Link with -lkeccak.

DESCRIPTION
       The libkeccak_update() function continues (or starts) hashing a
       message.  The current state of the hashing is stored in *state, and
       will be updated. The message specified by the msg parameter with the
       byte-size specified by the msglen parameter, will be hashed.

       The libkeccak_update() function may reallocate the state's message
       chunk buffer.  When doing so, it attempts to do so as securely as
       possible, rather than as fast as possible.

RETURN VALUES
       The libkeccak_update() function returns 0 upon successful completion.
       On error, -1 is returned and errno is set to describe the error.

ERRORS
       The libkeccak_update() function may fail for any reason specified by
       the function malloc(3).

NOTES
       Neither parameter by be NULL or 0.

EXAMPLE
       This example calculates the Keccak[b = 1024, c = 576, n = 256] hash of
       the input from stdin, and prints the hash, in hexadecimal form, to
       stdout.

       struct libkeccak_state state;
       struct libkeccak_spec spec;
       char binhash[256 / 8];
       char hexhash[256 / 8 * 2 + 1];
       char chunk[4 << 10];
       ssize_t len;

       spec.bitrate = 1024;
       spec.capacity = 576;
       spec.output = 256;
       if (libkeccak_state_initialise(&state, &spec) < 0)
            goto fail;

       for (;;) {
            len = read(STDIN_FILENO, chunk, sizeof(chunk));

            if ((len < 0) && (errno == EINTR))
                 continue;
            if (len < 0)
                 goto fail;
            if (len == 0)
                 break;

            if (libkeccak_update(&state, chunk, (size_t)len) < 0)
                 goto fail;
       }
       if (libkeccak_digest(&state, NULL, 0, 0, "", binhash) < 0)
            goto fail;

       libkeccak_behex_lower(hexhash, binhash, sizeof(binhash));
       printf("%s\n", hexhash);
       libkeccak_state_destroy(&state);

NOTES
       For cSHAKE, the libkeccak_cshake_initialise(3), must be called, once,
       immediately after state initialisation; before the first call to the
       libkeccak_update() function.

SEE ALSO
       libkeccak_state_initialise(3), libkeccak_cshake_initialise(3),
       libkeccak_fast_update(3), libkeccak_zerocopy_update(3),
       libkeccak_fast_digest(3), libkeccak_zerocopy_digest(3),
       libkeccak_digest(3)

                                   LIBKECCAK               LIBKECCAK_UPDATE(3)