Moved sha3 from `obscuren`

1 files changed, 216 insertions, 0 deletions

diff --git a/crypto/sha3/sha3.go b/crypto/sha3/sha3.go
new file mode 100644
index 000000000..22df0ef11
--- /dev/null
+++ b/crypto/sha3/sha3.go
@@ -0,0 +1,216 @@
+// Copyright 2013 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 implements the SHA3 hash algorithm (formerly called Keccak) chosen by NIST in 2012.
+// This file provides a SHA3 implementation which implements the standard hash.Hash interface.
+// Writing input data, including padding, and reading output data are computed in this file.
+// Note that the current implementation can compute the hash of an integral number of bytes only.
+// This is a consequence of the hash interface in which a buffer of bytes is passed in.
+// The internals of the Keccak-f function are computed in keccakf.go.
+// For the detailed specification, refer to the Keccak web site (http://keccak.noekeon.org/).
+package sha3
+
+import (
+	"encoding/binary"
+	"hash"
+)
+
+// laneSize is the size in bytes of each "lane" of the internal state of SHA3 (5 * 5 * 8).
+// Note that changing this size would requires using a type other than uint64 to store each lane.
+const laneSize = 8
+
+// sliceSize represents the dimensions of the internal state, a square matrix of
+// sliceSize ** 2 lanes. This is the size of both the "rows" and "columns" dimensions in the
+// terminology of the SHA3 specification.
+const sliceSize = 5
+
+// numLanes represents the total number of lanes in the state.
+const numLanes = sliceSize * sliceSize
+
+// stateSize is the size in bytes of the internal state of SHA3 (5 * 5 * WSize).
+const stateSize = laneSize * numLanes
+
+// digest represents the partial evaluation of a checksum.
+// Note that capacity, and not outputSize, is the critical security parameter, as SHA3 can output
+// an arbitrary number of bytes for any given capacity. The Keccak proposal recommends that
+// capacity = 2*outputSize to ensure that finding a collision of size outputSize requires
+// O(2^{outputSize/2}) computations (the birthday lower bound). Future standards may modify the
+// capacity/outputSize ratio to allow for more output with lower cryptographic security.
+type digest struct {
+	a          [numLanes]uint64  // main state of the hash
+	b          [numLanes]uint64  // intermediate states
+	c          [sliceSize]uint64 // intermediate states
+	d          [sliceSize]uint64 // intermediate states
+	outputSize int               // desired output size in bytes
+	capacity   int               // number of bytes to leave untouched during squeeze/absorb
+	absorbed   int               // number of bytes absorbed thus far
+}
+
+// minInt returns the lesser of two integer arguments, to simplify the absorption routine.
+func minInt(v1, v2 int) int {
+	if v1 <= v2 {
+		return v1
+	}
+	return v2
+}
+
+// rate returns the number of bytes of the internal state which can be absorbed or squeezed
+// in between calls to the permutation function.
+func (d *digest) rate() int {
+	return stateSize - d.capacity
+}
+
+// Reset clears the internal state by zeroing bytes in the state buffer.
+// This can be skipped for a newly-created hash state; the default zero-allocated state is correct.
+func (d *digest) Reset() {
+	d.absorbed = 0
+	for i := range d.a {
+		d.a[i] = 0
+	}
+}
+
+// BlockSize, required by the hash.Hash interface, does not have a standard intepretation
+// for a sponge-based construction like SHA3. We return the data rate: the number of bytes which
+// can be absorbed per invocation of the permutation function. For Merkle-Damgård based hashes
+// (ie SHA1, SHA2, MD5) the output size of the internal compression function is returned.
+// We consider this to be roughly equivalent because it represents the number of bytes of output
+// produced per cryptographic operation.
+func (d *digest) BlockSize() int { return d.rate() }
+
+// Size returns the output size of the hash function in bytes.
+func (d *digest) Size() int {
+	return d.outputSize
+}
+
+// unalignedAbsorb is a helper function for Write, which absorbs data that isn't aligned with an
+// 8-byte lane. This requires shifting the individual bytes into position in a uint64.
+func (d *digest) unalignedAbsorb(p []byte) {
+	var t uint64
+	for i := len(p) - 1; i >= 0; i-- {
+		t <<= 8
+		t |= uint64(p[i])
+	}
+	offset := (d.absorbed) % d.rate()
+	t <<= 8 * uint(offset%laneSize)
+	d.a[offset/laneSize] ^= t
+	d.absorbed += len(p)
+}
+
+// Write "absorbs" bytes into the state of the SHA3 hash, updating as needed when the sponge
+// "fills up" with rate() bytes. Since lanes are stored internally as type uint64, this requires
+// converting the incoming bytes into uint64s using a little endian interpretation. This
+// implementation is optimized for large, aligned writes of multiples of 8 bytes (laneSize).
+// Non-aligned or uneven numbers of bytes require shifting and are slower.
+func (d *digest) Write(p []byte) (int, error) {
+	// An initial offset is needed if the we aren't absorbing to the first lane initially.
+	offset := d.absorbed % d.rate()
+	toWrite := len(p)
+
+	// The first lane may need to absorb unaligned and/or incomplete data.
+	if (offset%laneSize != 0 || len(p) < 8) && len(p) > 0 {
+		toAbsorb := minInt(laneSize-(offset%laneSize), len(p))
+		d.unalignedAbsorb(p[:toAbsorb])
+		p = p[toAbsorb:]
+		offset = (d.absorbed) % d.rate()
+
+		// For every rate() bytes absorbed, the state must be permuted via the F Function.
+		if (d.absorbed)%d.rate() == 0 {
+			d.keccakF()
+		}
+	}
+
+	// This loop should absorb the bulk of the data into full, aligned lanes.
+	// It will call the update function as necessary.
+	for len(p) > 7 {
+		firstLane := offset / laneSize
+		lastLane := minInt(d.rate()/laneSize, firstLane+len(p)/laneSize)
+
+		// This inner loop absorbs input bytes into the state in groups of 8, converted to uint64s.
+		for lane := firstLane; lane < lastLane; lane++ {
+			d.a[lane] ^= binary.LittleEndian.Uint64(p[:laneSize])
+			p = p[laneSize:]
+		}
+		d.absorbed += (lastLane - firstLane) * laneSize
+		// For every rate() bytes absorbed, the state must be permuted via the F Function.
+		if (d.absorbed)%d.rate() == 0 {
+			d.keccakF()
+		}
+
+		offset = 0
+	}
+
+	// If there are insufficient bytes to fill the final lane, an unaligned absorption.
+	// This should always start at a correct lane boundary though, or else it would be caught
+	// by the uneven opening lane case above.
+	if len(p) > 0 {
+		d.unalignedAbsorb(p)
+	}
+
+	return toWrite, nil
+}
+
+// pad computes the SHA3 padding scheme based on the number of bytes absorbed.
+// The padding is a 1 bit, followed by an arbitrary number of 0s and then a final 1 bit, such that
+// the input bits plus padding bits are a multiple of rate(). Adding the padding simply requires
+// xoring an opening and closing bit into the appropriate lanes.
+func (d *digest) pad() {
+	offset := d.absorbed % d.rate()
+	// The opening pad bit must be shifted into position based on the number of bytes absorbed
+	padOpenLane := offset / laneSize
+	d.a[padOpenLane] ^= 0x0000000000000001 << uint(8*(offset%laneSize))
+	// The closing padding bit is always in the last position
+	padCloseLane := (d.rate() / laneSize) - 1
+	d.a[padCloseLane] ^= 0x8000000000000000
+}
+
+// finalize prepares the hash to output data by padding and one final permutation of the state.
+func (d *digest) finalize() {
+	d.pad()
+	d.keccakF()
+}
+
+// squeeze outputs an arbitrary number of bytes from the hash state.
+// Squeezing can require multiple calls to the F function (one per rate() bytes squeezed),
+// although this is not the case for standard SHA3 parameters. This implementation only supports
+// squeezing a single time, subsequent squeezes may lose alignment. Future implementations
+// may wish to support multiple squeeze calls, for example to support use as a PRNG.
+func (d *digest) squeeze(in []byte, toSqueeze int) []byte {
+	// Because we read in blocks of laneSize, we need enough room to read
+	// an integral number of lanes
+	needed := toSqueeze + (laneSize-toSqueeze%laneSize)%laneSize
+	if cap(in)-len(in) < needed {
+		newIn := make([]byte, len(in), len(in)+needed)
+		copy(newIn, in)
+		in = newIn
+	}
+	out := in[len(in) : len(in)+needed]
+
+	for len(out) > 0 {
+		for i := 0; i < d.rate() && len(out) > 0; i += laneSize {
+			binary.LittleEndian.PutUint64(out[:], d.a[i/laneSize])
+			out = out[laneSize:]
+		}
+		if len(out) > 0 {
+			d.keccakF()
+		}
+	}
+	return in[:len(in)+toSqueeze] // Re-slice in case we wrote extra data.
+}
+
+// Sum applies padding to the hash state and then squeezes out the desired nubmer of output bytes.
+func (d *digest) Sum(in []byte) []byte {
+	// Make a copy of the original hash so that caller can keep writing and summing.
+	dup := *d
+	dup.finalize()
+	return dup.squeeze(in, dup.outputSize)
+}
+
+// The NewKeccakX constructors enable initializing a hash in any of the four recommend sizes
+// from the Keccak specification, all of which set capacity=2*outputSize. Note that the final
+// NIST standard for SHA3 may specify different input/output lengths.
+// The output size is indicated in bits but converted into bytes internally.
+func NewKeccak224() hash.Hash { return &digest{outputSize: 224 / 8, capacity: 2 * 224 / 8} }
+func NewKeccak256() hash.Hash { return &digest{outputSize: 256 / 8, capacity: 2 * 256 / 8} }
+func NewKeccak384() hash.Hash { return &digest{outputSize: 384 / 8, capacity: 2 * 384 / 8} }
+func NewKeccak512() hash.Hash { return &digest{outputSize: 512 / 8, capacity: 2 * 512 / 8} }