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crypto/des: faster permutation.
This patch introduces specialized functions for initial and final permutations, and precomputes the output of the third permutation on the S-box elements. benchmark old ns/op new ns/op delta BenchmarkEncrypt 3581 1226 -65.76% BenchmarkDecrypt 3590 1224 -65.91% benchmark old MB/s new MB/s speedup BenchmarkEncrypt 2.23 6.52 2.92x BenchmarkDecrypt 2.23 6.53 2.93x R=golang-dev, rsc CC=golang-dev https://golang.org/cl/12072045
This commit is contained in:
Rémy Oudompheng
parent
d43ee1b714
commit
441ef7978d
@ -10,7 +10,7 @@ import (
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func cryptBlock(subkeys []uint64, dst, src []byte, decrypt bool) {
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b := binary.BigEndian.Uint64(src)
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b = permuteBlock(b, initialPermutation[:])
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b = permuteInitialBlock(b)
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left, right := uint32(b>>32), uint32(b)
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var subkey uint64
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@ -25,7 +25,7 @@ func cryptBlock(subkeys []uint64, dst, src []byte, decrypt bool) {
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}
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// switch left & right and perform final permutation
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preOutput := (uint64(right) << 32) | uint64(left)
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binary.BigEndian.PutUint64(dst, permuteBlock(preOutput, finalPermutation[:]))
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binary.BigEndian.PutUint64(dst, permuteFinalBlock(preOutput))
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}
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// Encrypt one block from src into dst, using the subkeys.
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@ -46,14 +46,18 @@ func feistel(right uint32, key uint64) (result uint32) {
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sBoxLocation := uint8(sBoxLocations>>42) & 0x3f
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sBoxLocations <<= 6
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// row determined by 1st and 6th bit
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row := (sBoxLocation & 0x1) | ((sBoxLocation & 0x20) >> 4)
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// column is middle four bits
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row := (sBoxLocation & 0x1) | ((sBoxLocation & 0x20) >> 4)
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column := (sBoxLocation >> 1) & 0xf
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sBoxResult |= uint32(sBoxes[i][row][column]) << (4 * (7 - i))
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sBoxResult ^= feistelBox[i][16*row+column]
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}
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return uint32(permuteBlock(uint64(sBoxResult), permutationFunction[:]))
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return sBoxResult
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}
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// feistelBox[s][16*i+j] contains the output of permutationFunction
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// for sBoxes[s][i][j] << 4*(7-s)
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var feistelBox [8][64]uint32
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// general purpose function to perform DES block permutations
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func permuteBlock(src uint64, permutation []uint8) (block uint64) {
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for position, n := range permutation {
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@ -63,18 +67,127 @@ func permuteBlock(src uint64, permutation []uint8) (block uint64) {
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return
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}
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func init() {
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for s := range sBoxes {
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for i := 0; i < 4; i++ {
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for j := 0; j < 16; j++ {
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f := uint64(sBoxes[s][i][j]) << (4 * (7 - uint(s)))
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f = permuteBlock(uint64(f), permutationFunction[:])
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feistelBox[s][16*i+j] = uint32(f)
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}
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}
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}
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}
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// expandBlock expands an input block of 32 bits,
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// producing an output block of 48 bits.
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func expandBlock(src uint32) (block uint64) {
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// rotate the 5 highest bits to the right.
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src = (src << 5) | (src >> 27)
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for i := 0; i < 8; i++ {
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block <<= 6
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// take the 6 bits on the right
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block |= uint64(src) & (1<<6 - 1)
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// advance by 4 bits.
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src = (src << 4) | (src >> 28)
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}
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return
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}
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// permuteInitialBlock is equivalent to the permutation defined
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// by initialPermutation.
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func permuteInitialBlock(block uint64) uint64 {
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// block = b7 b6 b5 b4 b3 b2 b1 b0 (8 bytes)
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b1 := block >> 48
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b2 := block << 48
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block ^= b1 ^ b2 ^ b1<<48 ^ b2>>48
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// block = b1 b0 b5 b4 b3 b2 b7 b6
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b1 = block >> 32 & 0xff00ff
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b2 = (block & 0xff00ff00)
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block ^= b1<<32 ^ b2 ^ b1<<8 ^ b2<<24 // exchange b0 b4 with b3 b7
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// block is now b1 b3 b5 b7 b0 b2 b4 b7, the permutation:
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// ... 8
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// ... 24
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// ... 40
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// ... 56
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// 7 6 5 4 3 2 1 0
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// 23 22 21 20 19 18 17 16
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// ... 32
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// ... 48
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// exchange 4,5,6,7 with 32,33,34,35 etc.
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b1 = block & 0x0f0f00000f0f0000
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b2 = block & 0x0000f0f00000f0f0
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block ^= b1 ^ b2 ^ b1>>12 ^ b2<<12
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// block is the permutation:
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//
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// [+8] [+40]
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//
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// 7 6 5 4
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// 23 22 21 20
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// 3 2 1 0
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// 19 18 17 16 [+32]
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// exchange 0,1,4,5 with 18,19,22,23
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b1 = block & 0x3300330033003300
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b2 = block & 0x00cc00cc00cc00cc
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block ^= b1 ^ b2 ^ b1>>6 ^ b2<<6
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// block is the permutation:
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// 15 14
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// 13 12
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// 11 10
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// 9 8
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// 7 6
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// 5 4
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// 3 2
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// 1 0 [+16] [+32] [+64]
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// exchange 0,2,4,6 with 9,11,13,15:
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b1 = block & 0xaaaaaaaa55555555
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block ^= b1 ^ b1>>33 ^ b1<<33
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// block is the permutation:
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// 6 14 22 30 38 46 54 62
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// 4 12 20 28 36 44 52 60
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// 2 10 18 26 34 42 50 58
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// 0 8 16 24 32 40 48 56
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// 7 15 23 31 39 47 55 63
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// 5 13 21 29 37 45 53 61
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// 3 11 19 27 35 43 51 59
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// 1 9 17 25 33 41 49 57
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return block
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}
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// permuteInitialBlock is equivalent to the permutation defined
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// by finalPermutation.
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func permuteFinalBlock(block uint64) uint64 {
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// Perform the same bit exchanges as permuteInitialBlock
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// but in reverse order.
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b1 := block & 0xaaaaaaaa55555555
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block ^= b1 ^ b1>>33 ^ b1<<33
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b1 = block & 0x3300330033003300
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b2 := block & 0x00cc00cc00cc00cc
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block ^= b1 ^ b2 ^ b1>>6 ^ b2<<6
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b1 = block & 0x0f0f00000f0f0000
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b2 = block & 0x0000f0f00000f0f0
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block ^= b1 ^ b2 ^ b1>>12 ^ b2<<12
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b1 = block >> 32 & 0xff00ff
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b2 = (block & 0xff00ff00)
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block ^= b1<<32 ^ b2 ^ b1<<8 ^ b2<<24
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b1 = block >> 48
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b2 = block << 48
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block ^= b1 ^ b2 ^ b1<<48 ^ b2>>48
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return block
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}
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// creates 16 28-bit blocks rotated according
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// to the rotation schedule
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func ksRotate(in uint32) (out []uint32) {
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@ -32,6 +32,17 @@ var finalPermutation = [64]byte{
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31, 63, 23, 55, 15, 47, 7, 39,
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}
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// Used to expand an input block of 32 bits, producing an output block of 48
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// bits.
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var expansionFunction = [48]byte{
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0, 31, 30, 29, 28, 27, 28, 27,
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26, 25, 24, 23, 24, 23, 22, 21,
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20, 19, 20, 19, 18, 17, 16, 15,
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16, 15, 14, 13, 12, 11, 12, 11,
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10, 9, 8, 7, 8, 7, 6, 5,
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4, 3, 4, 3, 2, 1, 0, 31,
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}
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// Yields a 32-bit output from a 32-bit input
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var permutationFunction = [32]byte{
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16, 25, 12, 11, 3, 20, 4, 15,
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@ -1504,6 +1504,39 @@ func TestSubstitutionTableKnownAnswerDecrypt(t *testing.T) {
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}
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}
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func TestInitialPermute(t *testing.T) {
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for i := uint(0); i < 64; i++ {
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bit := uint64(1) << i
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got := permuteInitialBlock(bit)
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want := uint64(1) << finalPermutation[63-i]
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if got != want {
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t.Errorf("permute(%x) = %x, want %x", bit, got, want)
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}
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}
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}
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func TestFinalPermute(t *testing.T) {
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for i := uint(0); i < 64; i++ {
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bit := uint64(1) << i
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got := permuteFinalBlock(bit)
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want := uint64(1) << initialPermutation[63-i]
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if got != want {
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t.Errorf("permute(%x) = %x, want %x", bit, got, want)
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}
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}
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}
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func TestExpandBlock(t *testing.T) {
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for i := uint(0); i < 32; i++ {
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bit := uint32(1) << i
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got := expandBlock(bit)
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want := permuteBlock(uint64(bit), expansionFunction[:])
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if got != want {
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t.Errorf("expand(%x) = %x, want %x", bit, got, want)
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}
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}
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}
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func BenchmarkEncrypt(b *testing.B) {
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tt := encryptDESTests[0]
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c, err := NewCipher(tt.key)
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