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.TH LIBKECCAK_HMAC_DIGEST 3 LIBKECCAK
.SH NAME
libkeccak_hmac_digest - Complete the HMAC-hashing of a message with erasure
.SH SYNOPSIS
.LP
.nf
#include <libkeccak.h>
.P
int
libkeccak_hmac_digest(libkeccak_hmac_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
.IR -lkeccak .
.SH DESCRIPTION
The
.BR libkeccak_hmac_digest ()
function absorbes the last part of (or all of) a message,
and returns the HMAC 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_hmac_update (3)
function or the
.BR libkeccak_hmac_fast_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 "" 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) are used.
.PP
The hash of the message will be stored to
.IR hashsum ,
unless
.I hashsum
is
.I 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_hmac_digest ()
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.
.SH RETURN VALUES
The
.BR libkeccak_hmac_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_hmac_digest ()
function may fail for any reason specified by the function
.BR malloc (3).
.SH SEE ALSO
.BR libkeccak_hmac_create (3),
.BR libkeccak_hmac_initialise (3),
.BR libkeccak_hmac_update (3),
.BR libkeccak_hmac_fast_digest (3),
.SH BUGS
Please report bugs to https://github.com/maandree/libkeccak/issues or to
maandree@kth.se
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