1 // Copyright 2014 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
7 // spongeDirection indicates the direction bytes are flowing through the sponge.
8 type spongeDirection int
11 // spongeAbsorbing indicates that the sponge is absorbing input.
12 spongeAbsorbing spongeDirection = iota
13 // spongeSqueezing indicates that the sponge is being squeezed.
18 // maxRate is the maximum size of the internal buffer. SHAKE-256
19 // currently needs the largest buffer.
24 // Generic sponge components.
25 a [25]uint64 // main state of the hash
26 buf []byte // points into storage
27 rate int // the number of bytes of state to use
29 // dsbyte contains the "domain separation" bits and the first bit of
30 // the padding. Sections 6.1 and 6.2 of [1] separate the outputs of the
31 // SHA-3 and SHAKE functions by appending bitstrings to the message.
32 // Using a little-endian bit-ordering convention, these are "01" for SHA-3
33 // and "1111" for SHAKE, or 00000010b and 00001111b, respectively. Then the
34 // padding rule from section 5.1 is applied to pad the message to a multiple
35 // of the rate, which involves adding a "1" bit, zero or more "0" bits, and
36 // a final "1" bit. We merge the first "1" bit from the padding into dsbyte,
37 // giving 00000110b (0x06) and 00011111b (0x1f).
38 // [1] http://csrc.nist.gov/publications/drafts/fips-202/fips_202_draft.pdf
39 // "Draft FIPS 202: SHA-3 Standard: Permutation-Based Hash and
40 // Extendable-Output Functions (May 2014)"
44 // Specific to SHA-3 and SHAKE.
45 fixedOutput bool // whether this is a fixed-output-length instance
46 outputLen int // the default output size in bytes
47 state spongeDirection // whether the sponge is absorbing or squeezing
50 // BlockSize returns the rate of sponge underlying this hash function.
51 func (d *state) BlockSize() int { return d.rate }
53 // Size returns the output size of the hash function in bytes.
54 func (d *state) Size() int { return d.outputLen }
56 // Reset clears the internal state by zeroing the sponge state and
57 // the byte buffer, and setting Sponge.state to absorbing.
58 func (d *state) Reset() {
59 // Zero the permutation's state.
63 d.state = spongeAbsorbing
67 func (d *state) clone() *state {
69 if ret.state == spongeAbsorbing {
70 ret.buf = ret.storage[:len(ret.buf)]
72 ret.buf = ret.storage[d.rate-cap(d.buf) : d.rate]
78 // permute applies the KeccakF-1600 permutation. It handles
79 // any input-output buffering.
80 func (d *state) permute() {
83 // If we're absorbing, we need to xor the input into the state
84 // before applying the permutation.
89 // If we're squeezing, we need to apply the permutatin before
90 // copying more output.
92 d.buf = d.storage[:d.rate]
97 // pads appends the domain separation bits in dsbyte, applies
98 // the multi-bitrate 10..1 padding rule, and permutes the state.
99 func (d *state) padAndPermute(dsbyte byte) {
101 d.buf = d.storage[:0]
103 // Pad with this instance's domain-separator bits. We know that there's
104 // at least one byte of space in d.buf because, if it were full,
105 // permute would have been called to empty it. dsbyte also contains the
106 // first one bit for the padding. See the comment in the state struct.
107 d.buf = append(d.buf, dsbyte)
108 zerosStart := len(d.buf)
109 d.buf = d.storage[:d.rate]
110 for i := zerosStart; i < d.rate; i++ {
113 // This adds the final one bit for the padding. Because of the way that
114 // bits are numbered from the LSB upwards, the final bit is the MSB of
116 d.buf[d.rate-1] ^= 0x80
117 // Apply the permutation
119 d.state = spongeSqueezing
120 d.buf = d.storage[:d.rate]
124 // Write absorbs more data into the hash's state. It produces an error
125 // if more data is written to the ShakeHash after writing
126 func (d *state) Write(p []byte) (written int, err error) {
127 if d.state != spongeAbsorbing {
128 panic("sha3: write to sponge after read")
131 d.buf = d.storage[:0]
136 if len(d.buf) == 0 && len(p) >= d.rate {
137 // The fast path; absorb a full "rate" bytes of input and apply the permutation.
142 // The slow path; buffer the input until we can fill the sponge, and then xor it in.
143 todo := d.rate - len(d.buf)
147 d.buf = append(d.buf, p[:todo]...)
150 // If the sponge is full, apply the permutation.
151 if len(d.buf) == d.rate {
160 // Read squeezes an arbitrary number of bytes from the sponge.
161 func (d *state) Read(out []byte) (n int, err error) {
162 // If we're still absorbing, pad and apply the permutation.
163 if d.state == spongeAbsorbing {
164 d.padAndPermute(d.dsbyte)
169 // Now, do the squeezing.
171 n := copy(out, d.buf)
175 // Apply the permutation if we've squeezed the sponge dry.
184 // Sum applies padding to the hash state and then squeezes out the desired
185 // number of output bytes.
186 func (d *state) Sum(in []byte) []byte {
187 // Make a copy of the original hash so that caller can keep writing
190 hash := make([]byte, dup.outputLen)
192 return append(in, hash...)