// 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.
fixedOutput bool // whether this is a fixed-ouput-length instance
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
}
d.state = spongeAbsorbing
d.buf = d.storage[:0]
}
func (d *state) clone() *state {
ret := *d
if ret.state == spongeAbsorbing {
ret.buf = ret.storage[:len(ret.buf)]
} else {
ret.buf = ret.storage[d.rate-cap(d.buf) : d.rate]
}
return &ret
}
// permute applies the KeccakF-1600 permutation. It handles
// any input-output buffering.
func (d *state) permute() {
switch d.state {
case spongeAbsorbing:
// If we're absorbing, we need to xor the input into the state
// before applying the permutation.
xorIn(d, d.buf)
d.buf = d.storage[:0]
keccakF1600(&d.a)
case spongeSqueezing:
// If we're squeezing, we need to apply the permutatin before
// copying more output.
keccakF1600(&d.a)
d.buf = d.storage[:d.rate]
copyOut(d, d.buf)
}
}
// pads appends the domain separation bits in dsbyte, applies
// the multi-bitrate 10..1 padding rule, and permutes the state.
func (d *state) padAndPermute(dsbyte byte) {
if d.buf == nil {
d.buf = d.storage[:0]
}
// Pad with this instance's domain-separator bits. We know that there's
// at least one byte of space in d.buf because, if it were full,
// permute would have been called to empty it. dsbyte also contains the
// first one bit for the padding. See the comment in the state struct.
d.buf = append(d.buf, dsbyte)
zerosStart := len(d.buf)
d.buf = d.storage[:d.rate]
for i := zerosStart; i < d.rate; i++ {
d.buf[i] = 0
}
// This adds the final one bit for the padding. Because of the way that
// bits are numbered from the LSB upwards, the final bit is the MSB of
// the last byte.
d.buf[d.rate-1] ^= 0x80
// Apply the permutation
d.permute()
d.state = spongeSqueezing
d.buf = d.storage[:d.rate]
copyOut(d, d.buf)
}
// Write absorbs more data into the hash's state. It produces an error
// if more data is written to the ShakeHash after writing
func (d *state) Write(p []byte) (written int, err error) {
if d.state != spongeAbsorbing {
panic("sha3: write to sponge after read")
}
if d.buf == nil {
d.buf = d.storage[:0]
}
written = len(p)
for len(p) > 0 {
if len(d.buf) == 0 && len(p) >= d.rate {
// The fast path; absorb a full "rate" bytes of input and apply the permutation.
xorIn(d, p[:d.rate])
p = p[d.rate:]
keccakF1600(&d.a)
} else {
// The slow path; buffer the input until we can fill the sponge, and then xor it in.
todo := d.rate - len(d.buf)
if todo > len(p) {
todo = len(p)
}
d.buf = append(d.buf, p[:todo]...)
p = p[todo:]
// If the sponge is full, apply the permutation.
if len(d.buf) == d.rate {
d.permute()
}
}
}
return
}
// Read squeezes an arbitrary number of bytes from the sponge.
func (d *state) Read(out []byte) (n int, err error) {
// If we're still absorbing, pad and apply the permutation.
if d.state == spongeAbsorbing {
d.padAndPermute(d.dsbyte)
}
n = len(out)
// Now, do the squeezing.
for len(out) > 0 {
n := copy(out, d.buf)
d.buf = d.buf[n:]
out = out[n:]
// Apply the permutation if we've squeezed the sponge dry.
if len(d.buf) == 0 {
d.permute()
}
}
return
}
// Sum applies padding to the hash state and then squeezes out the desired
// number of output bytes.
func (d *state) Sum(in []byte) []byte {
// Make a copy of the original hash so that caller can keep writing
// and summing.
dup := d.clone()
hash := make([]byte, dup.outputLen)
dup.Read(hash)
return append(in, hash...)
}
