.TH LIBKECCAK_FAST_DIGEST 3 LIBKECCAK-%VERSION%
.SH NAME
libkeccak_fast_digest - Complete the hashing of a message without erasure
.SH SYNOPSIS
.LP
.nf
#include <libkeccak.h>
.P
int libkeccak_fast_digest(libkeccak_state_t *\fIstate\fP, const char *\fImsg\fP, size_t \fImsglen\fP,
                          size_t \fIbits\fP, const char *\fIsuffix\fP, char *\fIhashsum\fP);
.fi
.P
Link with \fI-lkeccak\fP.
.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 \fImsg\fP parameter, and
its byte-size is specified by the \fImsglen\fP parameter. If
all of the message has already be processed by calls to the
.BR libkeccak_update (3)
function or the
.BR libkeccak_fast_update (3)
function (with the same pointer on \fIstate\fP,) \fImsg\fP
and \fImsglen\fP should be set to \fINULL\fP 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 \fIbits\fP parameter. \fImsglen\fP must only
count the number of whole bytes, that is, the floor of the
number of bits in the message divided by 8.
.PP
\fIsuffix\fP 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, \fINULL\fP may be used
instead. This is used to select hash algorithm. For pure Keccak,
\fINULL\fP or "" is used. For the other algorithms the constants
\fBLIBKECCAK_SHA3_SUFFIX\fP (for SHA-3),
\fBLIBKECCAK_RAWSHAKE_SUFFIX\fP (for RawSHAKE), and
\fBLIBKECCAK_SHAKE_SUFFIX\fP (for SHAKE) are used.
.PP
The hash of the message will be stored to \fIhashsum\fP,
unless \fIhashsum\fP is \fINULL\fP (which increases the
performance of the call.) A total of ((\fIstate->n\fP + 7) / 8)
bytes will be written to the beginning of \fIhashsum\fP.
Therefore, \fIhashsum\fP 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 \fIerrno\fP 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 SEE ALSO
.BR libkeccak_state_initialise (3),
.BR libkeccak_fast_update (3),
.BR libkeccak_update (3),
.BR libkeccak_digest (3),
.BR libkeccak_simple_squeeze (3),
.BR libkeccak_fast_squeeze (3),
.BR libkeccak_squeeze (3)
.SH AUTHORS
Principal author, Mattias Andrée.  See the LICENSE file for the full
list of authors.
.SH BUGS
Please report bugs to https://github.com/maandree/libkeccak/issues or to
maandree@member.fsf.org