vendor/golang.org/x/crypto/sha3/sha3.go

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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

// spongeDirection indicates the direction bytes are flowing through the sponge.
type spongeDirection int

const (
	// spongeAbsorbing indicates that the sponge is absorbing input.
	spongeAbsorbing spongeDirection = iota
	// spongeSqueezing indicates that the sponge is being squeezed.
	spongeSqueezing
)

const (
	// maxRate is the maximum size of the internal buffer. SHAKE-256
	// currently needs the largest buffer.
	maxRate = 168
)

type state struct {
	// Generic sponge components.
	a    [25]uint64 // main state of the hash
	buf  []byte     // points into storage
	rate int        // the number of bytes of state to use

	// dsbyte contains the "domain separation" bits and the first bit of
	// the padding. Sections 6.1 and 6.2 of [1] separate the outputs of the
	// SHA-3 and SHAKE functions by appending bitstrings to the message.
	// Using a little-endian bit-ordering convention, these are "01" for SHA-3
	// and "1111" for SHAKE, or 00000010b and 00001111b, respectively. Then the
	// padding rule from section 5.1 is applied to pad the message to a multiple
	// of the rate, which involves adding a "1" bit, zero or more "0" bits, and
	// a final "1" bit. We merge the first "1" bit from the padding into dsbyte,
	// giving 00000110b (0x06) and 00011111b (0x1f).
	// [1] http://csrc.nist.gov/publications/drafts/fips-202/fips_202_draft.pdf
	//     "Draft FIPS 202: SHA-3 Standard: Permutation-Based Hash and
	//      Extendable-Output Functions (May 2014)"
	dsbyte  byte
	storage [maxRate]byte

	// Specific to SHA-3 and SHAKE.
	outputLen int             // the default output size in bytes
	state     spongeDirection // whether the sponge is absorbing or squeezing
}

// BlockSize returns the rate of sponge underlying this hash function.
func (d *state) BlockSize() int { return d.rate }

// Size returns the output size of the hash function in bytes.
func (d *state) Size() int { return d.outputLen }

// Reset clears the internal state by zeroing the sponge state and
// the byte buffer, and setting Sponge.state to absorbing.
func (d *state) Reset() {
	// Zero the permutation's state.
	for i := range d.a {
		d.a[i] = 0