libkeccak_fast_digest.3

.TH LIBKECCAK_FAST_DIGEST 3 LIBKECCAK
.SH NAME
libkeccak_fast_digest - Complete the hashing of a message without erasure
.SH SYNOPSIS
.LP
.nf
#include <libkeccak.h>

int libkeccak_fast_digest(struct libkeccak_state *\fIstate\fP, const void *\fImsg\fP, size_t \fImsglen\fP,
                          size_t \fIbits\fP, const char *\fIsuffix\fP, void *\fIhashsum\fP);
.fi
.P
Link with
.IR -lkeccak .
.SH DESCRIPTION
The
.BR libkeccak_fast_digest ()
function absorbs the last part of (or all of) a message,
and returns the hash of the entire message. The last part
of the message is specified by the
.I msg
parameter, and its byte-size is specified by the
.I msglen
parameter. If all of the message has already be processed
by calls to the
.BR libkeccak_update (3),
.BR libkeccak_fast_update (3),
or
.BR libkeccak_zerocopy_update (3)
function (with the same pointer on
.IR state ,)
.I msg
and
.I msglen
should be set to
.I NULL
and 0, respectively.
.PP
If the message is not comprised a whole number of bytes,
the number of bits, modulus 8, in the message should be
specified in the
.I bits
parameter.
.I msglen
must only count the number of whole bytes, that is, the
floor of the number of bits in the message divided by 8.
.PP
.I suffix
should be a NUL-terminated string of ASCII '1':s and '0':s,
representing the bits that should be appended to the
message. If this string is empty,
.I NULL
may be used instead. This is used to select hash algorithm.
For pure Keccak,
.I NULL
or \(dq\(dq is used. For the other algorithms the constants
.B LIBKECCAK_SHA3_SUFFIX
(for SHA-3),
.B LIBKECCAK_RAWSHAKE_SUFFIX
(for RawSHAKE), and
.B LIBKECCAK_SHAKE_SUFFIX
(for SHAKE), or the return of the
.BR libkeccak_cshake_suffix (3)
function (for cSHAKE), are used.
.PP
The hash of the message will be stored to
.IR hashsum ,
unless
.IR hashsum
is
.IR NULL
(which increases the performance of the call.) A total of
.RI (( state->n
+ 7) / 8) bytes will be written to the beginning of
.IR hashsum .
Therefore,
.I hashsum
needs at least an allocation size of that number of bytes.
.PP
The
.BR libkeccak_fast_digest ()
function may reallocate the state's message chunk buffer.
When doing so, it attempts to do so as quickly as possible,
rather than ensuring that the information in the old
allocation is securely removed if a new allocation is required.
.SH RETURN VALUES
The
.BR libkeccak_fast_digest ()
function returns 0 upon successful completion. On error,
-1 is returned and
.I errno
is set to describe the error.
.SH ERRORS
The
.BR libkeccak_fast_digest ()
function may fail for any reason specified by the function
.BR realloc (3).
.SH 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.
.PP
.nf
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_fast_update(&state, chunk, (size_t)len) < 0)
		goto fail;
}
if (libkeccak_fast_digest(&state, NULL, 0, 0, \(dq\(dq, binhash) < 0)
	goto fail;

libkeccak_behex_lower(hexhash, binhash, sizeof(binhash));
printf(\(dq%s\en\(dq, hexhash);
libkeccak_state_fast_destroy(&state);
.fi
.SH NOTES
For cSHAKE, the
.BR libkeccak_cshake_initialise (3),
must be called, once, immediately after
state initialisation; before the first
call to any of the
.BR libkeccak_fast_update (),
.BR libkeccak_zerocopy_update (),
.BR libkeccak_update (),
and
.BR libkeccak_digest_digest ()
functions.
.SH SEE ALSO
.BR libkeccak_state_initialise (3),
.BR libkeccak_cshake_initialise (3),
.BR libkeccak_fast_update (3),
.BR libkeccak_zerocopy_update (3),
.BR libkeccak_update (3),
.BR libkeccak_cshake_suffix (3),
.BR libkeccak_digest (3),
.BR libkeccak_zerocopy_digest (3),
.BR libkeccak_simple_squeeze (3),
.BR libkeccak_fast_squeeze (3),
.BR libkeccak_squeeze (3)