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skein.go
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skein.go
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// Copyright 2012 Dmitry Chestnykh. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package skein implements the Skein-512 hash function, MAC, and stream cipher
// as defined in "The Skein Hash Function Family, v1.3".
package skein
import (
"crypto/cipher"
"errors"
"hash"
"io"
)
// Hash represents a state of Skein hash function.
// It implements hash.Hash interface.
type Hash struct {
k [8]uint64 // chain value
t [2]uint64 // tweak
x [64]byte // buffer
nx int // number of bytes in buffer
outLen uint64 // output length in bytes
noMsg bool // true if message block argument should not be used
ik [8]uint64 // copy of initial chain value
}
// Args can be used to configure hash function for different purposes.
// All fields are optional: if a field is nil, it will not be used.
type Args struct {
// Key is a secret key for MAC, KDF, or stream cipher
Key []byte
// Person is a personalization string
Person []byte
// PublicKey is a public key for signature hashing
PublicKey []byte
// KeyId is a key identifier for KDF
KeyId []byte
// Nonce for stream cipher or randomized hashing
Nonce []byte
// NoMsg indicates whether message input is used by the function.
//
// If false (default), message input it used, and thus if zero-length
// message is supplied to Write or if Write was not called, it will be
// assumed that the message input is zero-length, and thus will be
// processed as such (padded with zeroes). This is the normal way Skein
// hash and MAC are used.
//
// If true, message input is not used, so any call to Write will
// return an error. This is useful for constructions such as a
// that skip message input, such as a stream cipher.
//
// The name is negative to preserve backward compatibility.
NoMsg bool
}
// BlockSize is the block size of Skein-512 in bytes.
const BlockSize = 64
// Argument types (in the order they must be used).
const (
keyArg uint64 = 0
configArg uint64 = 4
personArg uint64 = 8
publicKeyArg uint64 = 12
keyIDArg uint64 = 16
nonceArg uint64 = 20
messageArg uint64 = 48
outputArg uint64 = 63
)
const (
firstBlockFlag uint64 = 1 << 62
lastBlockFlag uint64 = 1 << 63
)
var schemaId = []byte{'S', 'H', 'A', '3', 1, 0, 0, 0}
var outTweak = [2]uint64{8, outputArg<<56 | firstBlockFlag | lastBlockFlag}
// Precomputed initial values of state after configuration for unkeyed hashing.
var iv224 = [8]uint64{
0xCCD0616248677224, 0xCBA65CF3A92339EF, 0x8CCD69D652FF4B64, 0x398AED7B3AB890B4,
0x0F59D1B1457D2BD0, 0x6776FE6575D4EB3D, 0x99FBC70E997413E9, 0x9E2CFCCFE1C41EF7}
var iv256 = [8]uint64{
0xCCD044A12FDB3E13, 0xE83590301A79A9EB, 0x55AEA0614F816E6F, 0x2A2767A4AE9B94DB,
0xEC06025E74DD7683, 0xE7A436CDC4746251, 0xC36FBAF9393AD185, 0x3EEDBA1833EDFC13}
var iv384 = [8]uint64{
0xA3F6C6BF3A75EF5F, 0xB0FEF9CCFD84FAA4, 0x9D77DD663D770CFE, 0xD798CBF3B468FDDA,
0x1BC4A6668A0E4465, 0x7ED7D434E5807407, 0x548FC1ACD4EC44D6, 0x266E17546AA18FF8}
var iv512 = [8]uint64{
0x4903ADFF749C51CE, 0x0D95DE399746DF03, 0x8FD1934127C79BCE, 0x9A255629FF352CB1,
0x5DB62599DF6CA7B0, 0xEABE394CA9D5C3F4, 0x991112C71A75B523, 0xAE18A40B660FCC33}
func (h *Hash) hashBlock(b []byte, unpaddedLen uint64) {
var u [8]uint64
// Update block counter.
h.t[0] += unpaddedLen
u[0] = uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24 |
uint64(b[4])<<32 | uint64(b[5])<<40 | uint64(b[6])<<48 | uint64(b[7])<<56
u[1] = uint64(b[8]) | uint64(b[9])<<8 | uint64(b[10])<<16 | uint64(b[11])<<24 |
uint64(b[12])<<32 | uint64(b[13])<<40 | uint64(b[14])<<48 | uint64(b[15])<<56
u[2] = uint64(b[16]) | uint64(b[17])<<8 | uint64(b[18])<<16 | uint64(b[19])<<24 |
uint64(b[20])<<32 | uint64(b[21])<<40 | uint64(b[22])<<48 | uint64(b[23])<<56
u[3] = uint64(b[24]) | uint64(b[25])<<8 | uint64(b[26])<<16 | uint64(b[27])<<24 |
uint64(b[28])<<32 | uint64(b[29])<<40 | uint64(b[30])<<48 | uint64(b[31])<<56
u[4] = uint64(b[32]) | uint64(b[33])<<8 | uint64(b[34])<<16 | uint64(b[35])<<24 |
uint64(b[36])<<32 | uint64(b[37])<<40 | uint64(b[38])<<48 | uint64(b[39])<<56
u[5] = uint64(b[40]) | uint64(b[41])<<8 | uint64(b[42])<<16 | uint64(b[43])<<24 |
uint64(b[44])<<32 | uint64(b[45])<<40 | uint64(b[46])<<48 | uint64(b[47])<<56
u[6] = uint64(b[48]) | uint64(b[49])<<8 | uint64(b[50])<<16 | uint64(b[51])<<24 |
uint64(b[52])<<32 | uint64(b[53])<<40 | uint64(b[54])<<48 | uint64(b[55])<<56
u[7] = uint64(b[56]) | uint64(b[57])<<8 | uint64(b[58])<<16 | uint64(b[59])<<24 |
uint64(b[60])<<32 | uint64(b[61])<<40 | uint64(b[62])<<48 | uint64(b[63])<<56
block(&h.k, &h.t, &h.k, &u)
// Clear first block flag.
h.t[1] &^= firstBlockFlag
}
func (h *Hash) hashLastBlock() {
// Pad buffer with zeros.
for i := h.nx; i < len(h.x); i++ {
h.x[i] = 0
}
// Set last block flag.
h.t[1] |= lastBlockFlag
// Process last block.
h.hashBlock(h.x[:], uint64(h.nx))
h.nx = 0
}
func (h *Hash) outputBlock(dst *[64]byte, counter uint64) {
var u [8]uint64
u[0] = counter
block(&h.k, &outTweak, &u, &u)
for i, v := range u {
dst[i*8+0] = byte(v)
dst[i*8+1] = byte(v >> 8)
dst[i*8+2] = byte(v >> 16)
dst[i*8+3] = byte(v >> 24)
dst[i*8+4] = byte(v >> 32)
dst[i*8+5] = byte(v >> 40)
dst[i*8+6] = byte(v >> 48)
dst[i*8+7] = byte(v >> 56)
}
}
func (h *Hash) appendOutput(in []byte, length uint64) []byte {
var b [64]byte
var counter uint64
for length > 0 {
h.outputBlock(&b, counter)
counter++ // increment counter
if length < 64 {
in = append(in, b[:length]...)
break
}
in = append(in, b[:]...)
length -= 64
}
return in
}
func (h *Hash) update(b []byte) {
left := 64 - h.nx
if len(b) > left {
// Process leftovers.
copy(h.x[h.nx:], b[:left])
b = b[left:]
h.hashBlock(h.x[:], 64)
h.nx = 0
}
// Process full blocks except for the last one.
for len(b) > 64 {
h.hashBlock(b, 64)
b = b[64:]
}
// Save leftovers.
h.nx += copy(h.x[h.nx:], b)
}
// Write adds more data to the running hash.
// It never returns an error.
func (h *Hash) Write(b []byte) (n int, err error) {
if h.noMsg {
return 0, errors.New("Skein: can't write to a function configured with NoMsg")
}
h.update(b)
return len(b), nil
}
// Sum appends the current hash to in and returns the resulting slice.
// It does not change the underlying hash state.
func (h0 *Hash) Sum(in []byte) []byte {
// Make a copy of h0 so that caller can keep writing and summing.
h := new(Hash)
*h = *h0
if !h.noMsg {
// Finalize message.
h.hashLastBlock()
}
return h.appendOutput(in, h.outLen)
}
// BlockSize returns the hash's underlying block size.
func (h *Hash) BlockSize() int { return BlockSize }
// Size returns the number of bytes Sum will return.
// If the hash was created with output size greater than the maximum
// size of int, the result is undefined.
func (h *Hash) Size() int { return int(h.outLen) }
// Reset resets hash to its state after initialization.
// If hash was initialized with arguments, such as key,
// these arguments are preserved.
func (h *Hash) Reset() {
// Restore initial chain value.
h.k = h.ik
// Reset buffer.
h.nx = 0
// Init tweak to first message block.
h.t[0] = 0
h.t[1] = messageArg<<56 | firstBlockFlag
}
// OutputReader returns an io.Reader that can be used to read
// arbitrary-length output of the hash.
// Reading from it doesn't change the underlying hash state.
func (h *Hash) OutputReader() io.Reader {
return newOutputReader(h)
}
// outputReader implements io.Reader and cipher.Stream interfaces.
// It is used for reading arbitrary-length output of Skein.
type outputReader struct {
Hash
counter uint64
}
// newOutputReader returns a new outputReader initialized with
// a copy of the given hash.
func newOutputReader(h *Hash) *outputReader {
// Initialize with the copy of h.
r := &outputReader{Hash: *h}
if !r.noMsg {
// Finalize message.
r.hashLastBlock()
}
// Set buffer position to end.
r.nx = BlockSize
return r
}
// nextBlock puts the next hash output block into the internal buffer.
func (r *outputReader) nextBlock() {
r.outputBlock(&r.x, r.counter)
r.counter++ // increment counter
r.nx = 0
}
// Read puts the next len(p) bytes of hash output into p.
// It never returns an error.
func (r *outputReader) Read(p []byte) (n int, err error) {
n = len(p)
left := BlockSize - r.nx
if len(p) < left {
r.nx += copy(p, r.x[r.nx:r.nx+len(p)])
return
}
copy(p, r.x[r.nx:])
p = p[left:]
r.nextBlock()
for len(p) >= BlockSize {
copy(p, r.x[:])
p = p[BlockSize:]
r.nextBlock()
}
if len(p) > 0 {
r.nx += copy(p, r.x[:len(p)])
}
return
}
// XORKeyStream XORs each byte in the given slice with the next byte from the
// hash output. Dst and src may point to the same memory.
func (r *outputReader) XORKeyStream(dst, src []byte) {
left := BlockSize - r.nx
if len(src) < left {
for i, v := range src {
dst[i] = v ^ r.x[r.nx]
r.nx++
}
return
}
for i, b := range r.x[r.nx:] {
dst[i] = src[i] ^ b
}
dst = dst[left:]
src = src[left:]
r.nextBlock()
for len(src) >= BlockSize {
for i, v := range src[:BlockSize] {
dst[i] = v ^ r.x[i]
}
dst = dst[BlockSize:]
src = src[BlockSize:]
r.nextBlock()
}
if len(src) > 0 {
for i, v := range src {
dst[i] = v ^ r.x[i]
r.nx++
}
}
}
// addArg adds Skein argument into the hash state.
func (h *Hash) addArg(argType uint64, arg []byte) {
h.t[0] = 0
h.t[1] = argType<<56 | firstBlockFlag
h.update(arg)
h.hashLastBlock()
}
// addConfig adds configuration block into the hash state.
func (h *Hash) addConfig(outBits uint64) {
var c [32]byte
copy(c[:], schemaId)
c[8] = byte(outBits)
c[9] = byte(outBits >> 8)
c[10] = byte(outBits >> 16)
c[11] = byte(outBits >> 24)
c[12] = byte(outBits >> 32)
c[13] = byte(outBits >> 40)
c[14] = byte(outBits >> 48)
c[15] = byte(outBits >> 56)
h.addArg(configArg, c[:])
}
// New returns a new skein.Hash configured with the given arguments. The final
// output length of hash function in bytes is outLen (for example, 64 when
// calculating 512-bit hash). Configuration arguments may be nil.
func New(outLen uint64, args *Args) *Hash {
h := new(Hash)
h.outLen = outLen
if args != nil && args.Key != nil {
// Key argument comes before configuration.
h.addArg(keyArg, args.Key)
// Configuration.
h.addConfig(outLen * 8)
} else {
// Configuration without key.
// Try using precomputed values for common sizes.
switch outLen {
case 224 / 8:
h.k = iv224
case 256 / 8:
h.k = iv256
case 384 / 8:
h.k = iv384
case 512 / 8:
h.k = iv512
default:
h.addConfig(outLen * 8)
}
}
// Other arguments, in specified order.
if args != nil {
h.noMsg = args.NoMsg
if args.Person != nil {
h.addArg(personArg, args.Person)
}
if args.PublicKey != nil {
h.addArg(publicKeyArg, args.PublicKey)
}
if args.KeyId != nil {
h.addArg(keyIDArg, args.KeyId)
}
if args.Nonce != nil {
h.addArg(nonceArg, args.Nonce)
}
}
// Init tweak to first message block.
h.t[0] = 0
h.t[1] = messageArg<<56 | firstBlockFlag
// Save a copy of initial chain value for Reset.
h.ik = h.k
return h
}
// NewHash returns hash.Hash calculating checksum of the given length in bytes
// (for example, to calculate 256-bit hash, outLen must be set to 32).
func NewHash(outLen uint64) hash.Hash {
return hash.Hash(New(outLen, nil))
}
// NewMAC returns hash.Hash calculating Skein Message Authentication Code of the
// given length in bytes. A MAC is a cryptographic hash that uses a key to
// authenticate a message. The receiver verifies the hash by recomputing it
// using the same key.
func NewMAC(outLen uint64, key []byte) hash.Hash {
return hash.Hash(New(outLen, &Args{Key: key}))
}
// NewStream returns a cipher.Stream for encrypting a message with the given key
// and nonce. The same key-nonce combination must not be used to encrypt more
// than one message. There are no limits on the length of key or nonce.
func NewStream(key []byte, nonce []byte) cipher.Stream {
const streamOutLen = (1<<64 - 1) / 8 // 2^64 - 1 bits
h := New(streamOutLen, &Args{Key: key, Nonce: nonce, NoMsg: true})
return newOutputReader(h)
}