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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
// This file defines the ShakeHash interface, and provides
// functions for creating SHAKE and cSHAKE instances, as well as utility
// functions for hashing bytes to arbitrary-length output.
//
//
// SHAKE implementation is based on FIPS PUB 202 [1]
// cSHAKE implementations is based on NIST SP 800-185 [2]
//
// [1] https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.202.pdf
// [2] https://doi.org/10.6028/NIST.SP.800-185
import (
"encoding/binary"
"io"
)
// ShakeHash defines the interface to hash functions that
// support arbitrary-length output.
type ShakeHash interface {
// Write absorbs more data into the hash's state. It panics if input is
// written to it after output has been read from it.
io.Writer
// Read reads more output from the hash; reading affects the hash's
// state. (ShakeHash.Read is thus very different from Hash.Sum)
// It never returns an error.
io.Reader
// Clone returns a copy of the ShakeHash in its current state.
Clone() ShakeHash
// Reset resets the ShakeHash to its initial state.
Reset()
}
// cSHAKE specific context
type cshakeState struct {
*state // SHA-3 state context and Read/Write operations
// initBlock is the cSHAKE specific initialization set of bytes. It is initialized
// by newCShake function and stores concatenation of N followed by S, encoded
// by the method specified in 3.3 of [1].
// It is stored here in order for Reset() to be able to put context into
// initial state.
initBlock []byte
}
// Consts for configuring initial SHA-3 state
const (
dsbyteShake = 0x1f
dsbyteCShake = 0x04
rate128 = 168
rate256 = 136
)
func bytepad(input []byte, w int) []byte {
// leftEncode always returns max 9 bytes
buf := make([]byte, 0, 9+len(input)+w)
buf = append(buf, leftEncode(uint64(w))...)
buf = append(buf, input...)
padlen := w - (len(buf) % w)
return append(buf, make([]byte, padlen)...)
}
func leftEncode(value uint64) []byte {
var b [9]byte
binary.BigEndian.PutUint64(b[1:], value)
// Trim all but last leading zero bytes
i := byte(1)
for i < 8 && b[i] == 0 {
i++
}
// Prepend number of encoded bytes
b[i-1] = 9 - i
return b[i-1:]
}
func newCShake(N, S []byte, rate int, dsbyte byte) ShakeHash {
c := cshakeState{state: &state{rate: rate, dsbyte: dsbyte}}
// leftEncode returns max 9 bytes
c.initBlock = make([]byte, 0, 9*2+len(N)+len(S))
c.initBlock = append(c.initBlock, leftEncode(uint64(len(N)*8))...)
c.initBlock = append(c.initBlock, N...)
c.initBlock = append(c.initBlock, leftEncode(uint64(len(S)*8))...)
c.initBlock = append(c.initBlock, S...)
c.Write(bytepad(c.initBlock, c.rate))
return &c
}
// Reset resets the hash to initial state.
func (c *cshakeState) Reset() {
c.state.Reset()
c.Write(bytepad(c.initBlock, c.rate))
}
// Clone returns copy of a cSHAKE context within its current state.
func (c *cshakeState) Clone() ShakeHash {
b := make([]byte, len(c.initBlock))
copy(b, c.initBlock)
return &cshakeState{state: c.clone(), initBlock: b}
}
// Clone returns copy of SHAKE context within its current state.
func (c *state) Clone() ShakeHash {
return c.clone()
}
// NewShake128 creates a new SHAKE128 variable-output-length ShakeHash.
// Its generic security strength is 128 bits against all attacks if at
// least 32 bytes of its output are used.
func NewShake128() ShakeHash {
if h := newShake128Asm(); h != nil {
return h
}
return &state{rate: rate128, dsbyte: dsbyteShake}
}
// NewShake256 creates a new SHAKE256 variable-output-length ShakeHash.
// Its generic security strength is 256 bits against all attacks if
// at least 64 bytes of its output are used.
func NewShake256() ShakeHash {
if h := newShake256Asm(); h != nil {
return h
}
return &state{rate: rate256, dsbyte: dsbyteShake}
}
// NewCShake128 creates a new instance of cSHAKE128 variable-output-length ShakeHash,
// a customizable variant of SHAKE128.
// N is used to define functions based on cSHAKE, it can be empty when plain cSHAKE is
// desired. S is a customization byte string used for domain separation - two cSHAKE
// computations on same input with different S yield unrelated outputs.
// When N and S are both empty, this is equivalent to NewShake128.
func NewCShake128(N, S []byte) ShakeHash {
if len(N) == 0 && len(S) == 0 {
return NewShake128()
}
return newCShake(N, S, rate128, dsbyteCShake)
}
// NewCShake256 creates a new instance of cSHAKE256 variable-output-length ShakeHash,
// a customizable variant of SHAKE256.
// N is used to define functions based on cSHAKE, it can be empty when plain cSHAKE is
// desired. S is a customization byte string used for domain separation - two cSHAKE
// computations on same input with different S yield unrelated outputs.
// When N and S are both empty, this is equivalent to NewShake256.
func NewCShake256(N, S []byte) ShakeHash {
if len(N) == 0 && len(S) == 0 {
return NewShake256()
}
return newCShake(N, S, rate256, dsbyteCShake)
}
// ShakeSum128 writes an arbitrary-length digest of data into hash.
func ShakeSum128(hash, data []byte) {
h := NewShake128()
h.Write(data)
h.Read(hash)
}
// ShakeSum256 writes an arbitrary-length digest of data into hash.
func ShakeSum256(hash, data []byte) {
h := NewShake256()
h.Write(data)
h.Read(hash)
}
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