| // 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" |
