.\" $NetBSD: SHAKE.3,v 1.1 2017/11/30 16:00:48 wiz Exp $
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.\" Copyright (c) 2015 Taylor R. Campbell
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.Dd October 14, 2015
.Dt SHAKE 3
.Os
.Sh NAME
.Nm SHAKE
.Nd NIST FIPS PUB 202: SHA-3 Standard: Permutation-Based Hash and Extendable-Output Functions
.Sh SYNOPSIS
.In sha3.h
.Ft void
.Fn SHAKE128_Init "SHAKE128_CTX *ctx"
.Ft void
.Fn SHAKE128_Update "SHAKE128_CTX *ctx" "const uint8_t *buf" "size_t len"
.Ft void
.Fn SHAKE128_Final "uint8_t *output[]" "size_t outlen" "SHAKE128_CTX *ctx"
.Ft void
.Fn SHAKE256_Init "SHAKE256_CTX *ctx"
.Ft void
.Fn SHAKE256_Update "SHAKE256_CTX *ctx" "const uint8_t *buf" "size_t len"
.Ft void
.Fn SHAKE256_Final "uint8_t *output[]" "size_t outlen" "SHAKE256_CTX *ctx"
.Sh DESCRIPTION
The
.Nm
functions implement the extendable-output functions of the NIST SHA-3
standard, FIPS PUB 202.
The
.Nm
functions absorb an arbitrary-length message m and yield an
arbitrary-length output SHAKE128(m) or SHAKE256(m), truncated to a
specified number of octets.
.Pp
Before using the
.Nm
functions, applications should first call
.Xr SHA3_Selftest 3
and confirm that it succeeded.
.Pp
Only the
.Nm SHAKE128
functions are specified in detail; the
.Nm SHAKE256
functions are analogous.
.Pp
The caller must allocate memory for a
.Vt SHAKE128_CTX
object to hold the state of a SHAKE128 computation over a message.
.Vt SHAKE128_CTX
objects may be copied or relocated in memory.
.Bl -tag -width abcd
.It Fn SHAKE128_Init "ctx"
Initialize a SHAKE128 context.
Must be done before any other operations on
.Fa ctx .
.It Fn SHAKE128_Update "ctx" "data" "len"
Append
.Fa len
octets at
.Fa data
to the message.
.It Fn SHAKE128_Final "output" "outlen" "ctx"
Store at
.Fa output
the first
.Fa outlen
octets of the SHAKE128 output for the message obtained by concatenating
all prior inputs to
.Fn SHAKE128_Update
on
.Fa ctx .
.Pp
Subsequent use of
.Fa ctx
is not allowed, unless it is reinitialized with
.Fn SHAKE128_Init .
.El
.Sh SEE ALSO
.Xr keccak 3 ,
.Xr sha3 3 ,
.Xr SHA3_Selftest 3
.Sh STANDARDS
.Rs
.%A National Institute of Standards and Technology
.%T SHA-3 Standard: Permutation-Based Hash and Extendable-Output Functions
.%O FIPS PUB 202
.%D August 2015
.Re
.Sh AUTHORS
.An Taylor R Campbell Aq campbell+sha3@mumble.net