Commit 0e1108ba authored by Niels Möller's avatar Niels Möller

Document SHAKE-256.

parent 64a6def6
......@@ -8,6 +8,7 @@
* testsuite/shake.awk: New script to extract test vectors.
* testsuite/Makefile.in (TS_NETTLE_SOURCES): Add shake256-test.c.
(DISTFILES): Add shake.awk.
* nettle.texinfo (Recommended hash functions): Document SHAKE-256.
* sha3.c (_sha3_pad): Generalized with an argument for the magic
suffix defining the sha3 instance.
......
......@@ -834,6 +834,28 @@ octets of the digest are written.
This function also resets the context.
@end deftypefun
@subsubsection @acronym{SHAKE-256}
@cindex SHAKE
In addition to those SHA-3 hash functions, Nettle also provides a SHA-3
extendable-output function (XOF), SHAKE-256. Unlike SHA-3 hash functions,
SHAKE can produce an output digest of any desired length.
To use SHAKE256, the context struct, init and update functions are the
same as for SHA3-256. To get a SHAKE256 digest, the following function
is used instead of @code{sha3_256_digest}. For an output size of
@code{SHA3_256_DIGEST_SIZE}, security is equivalent to SHA3-256 (but the
digest is different). Increasing output size further does not increase
security in terms of collision or preimage resistance. It can be seen as
a built in pseudorandomness generator.
@deftypefun void sha3_256_shake (struct shake256_ctx *@var{ctx}, size_t @var{length}, uint8_t *@var{digest})
Performs final processing and produces a SHAKE256 digest, writing it
to @var{digest}. @var{length} can be of arbitrary size.
This function also resets the context.
@end deftypefun
@node Legacy hash functions, nettle_hash abstraction, Recommended hash functions, Hash functions
@comment node-name, next, previous, up
@subsection Legacy hash functions
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