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+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package sha3 implements the SHA-3 fixed-output-length hash functions and
+// the SHAKE variable-output-length hash functions defined by FIPS-202.
+//
+// Both types of hash function use the "sponge" construction and the Keccak
+// permutation. For a detailed specification see http://keccak.noekeon.org/
+//
+//
+// Guidance
+//
+// If you aren't sure what function you need, use SHAKE256 with at least 64
+// bytes of output. The SHAKE instances are faster than the SHA3 instances;
+// the latter have to allocate memory to conform to the hash.Hash interface.
+//
+// If you need a secret-key MAC (message authentication code), prepend the
+// secret key to the input, hash with SHAKE256 and read at least 32 bytes of
+// output.
+//
+//
+// Security strengths
+//
+// The SHA3-x (x equals 224, 256, 384, or 512) functions have a security
+// strength against preimage attacks of x bits. Since they only produce "x"
+// bits of output, their collision-resistance is only "x/2" bits.
+//
+// The SHAKE-256 and -128 functions have a generic security strength of 256 and
+// 128 bits against all attacks, provided that at least 2x bits of their output
+// is used.  Requesting more than 64 or 32 bytes of output, respectively, does
+// not increase the collision-resistance of the SHAKE functions.
+//
+//
+// The sponge construction
+//
+// A sponge builds a pseudo-random function from a public pseudo-random
+// permutation, by applying the permutation to a state of "rate + capacity"
+// bytes, but hiding "capacity" of the bytes.
+//
+// A sponge starts out with a zero state. To hash an input using a sponge, up
+// to "rate" bytes of the input are XORed into the sponge's state. The sponge
+// is then "full" and the permutation is applied to "empty" it. This process is
+// repeated until all the input has been "absorbed". The input is then padded.
+// The digest is "squeezed" from the sponge in the same way, except that output
+// output is copied out instead of input being XORed in.
+//
+// A sponge is parameterized by its generic security strength, which is equal
+// to half its capacity; capacity + rate is equal to the permutation's width.
+// Since the KeccakF-1600 permutation is 1600 bits (200 bytes) wide, this means
+// that the security strength of a sponge instance is equal to (1600 - bitrate) / 2.
+//
+//
+// Recommendations
+//
+// The SHAKE functions are recommended for most new uses. They can produce
+// output of arbitrary length. SHAKE256, with an output length of at least
+// 64 bytes, provides 256-bit security against all attacks.  The Keccak team
+// recommends it for most applications upgrading from SHA2-512. (NIST chose a
+// much stronger, but much slower, sponge instance for SHA3-512.)
+//
+// The SHA-3 functions are "drop-in" replacements for the SHA-2 functions.
+// They produce output of the same length, with the same security strengths
+// against all attacks. This means, in particular, that SHA3-256 only has
+// 128-bit collision resistance, because its output length is 32 bytes.
+package sha3 // import "golang.org/x/crypto/sha3"