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-rw-r--r--crypto/sha3/sha3.go193
1 files changed, 193 insertions, 0 deletions
diff --git a/crypto/sha3/sha3.go b/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.
+ 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...)
+}