1 files changed, 193 insertions, 0 deletions
diff --git a/crypto/sha3/sha3.go b/crypto/sha3/sha3.go
new file mode 100644
index 000000000..c8fd31cb0
--- /dev/null
+++ b/crypto/sha3/sha3.go
@@ -0,0 +1,193 @@
+// 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...)
+}