264 lines
6.9 KiB
Go
264 lines
6.9 KiB
Go
// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package des
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import (
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"encoding/binary"
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"sync"
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)
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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 = permuteInitialBlock(b)
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left, right := uint32(b>>32), uint32(b)
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left = (left << 1) | (left >> 31)
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right = (right << 1) | (right >> 31)
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if decrypt {
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for i := 0; i < 8; i++ {
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left, right = feistel(left, right, subkeys[15-2*i], subkeys[15-(2*i+1)])
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}
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} else {
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for i := 0; i < 8; i++ {
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left, right = feistel(left, right, subkeys[2*i], subkeys[2*i+1])
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}
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}
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left = (left << 31) | (left >> 1)
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right = (right << 31) | (right >> 1)
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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, permuteFinalBlock(preOutput))
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}
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// Encrypt one block from src into dst, using the subkeys.
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func encryptBlock(subkeys []uint64, dst, src []byte) {
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cryptBlock(subkeys, dst, src, false)
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}
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// Decrypt one block from src into dst, using the subkeys.
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func decryptBlock(subkeys []uint64, dst, src []byte) {
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cryptBlock(subkeys, dst, src, true)
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}
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// DES Feistel function. feistelBox must be initialized via
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// feistelBoxOnce.Do(initFeistelBox) first.
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func feistel(l, r uint32, k0, k1 uint64) (lout, rout uint32) {
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var t uint32
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t = r ^ uint32(k0>>32)
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l ^= feistelBox[7][t&0x3f] ^
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feistelBox[5][(t>>8)&0x3f] ^
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feistelBox[3][(t>>16)&0x3f] ^
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feistelBox[1][(t>>24)&0x3f]
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t = ((r << 28) | (r >> 4)) ^ uint32(k0)
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l ^= feistelBox[6][(t)&0x3f] ^
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feistelBox[4][(t>>8)&0x3f] ^
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feistelBox[2][(t>>16)&0x3f] ^
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feistelBox[0][(t>>24)&0x3f]
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t = l ^ uint32(k1>>32)
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r ^= feistelBox[7][t&0x3f] ^
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feistelBox[5][(t>>8)&0x3f] ^
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feistelBox[3][(t>>16)&0x3f] ^
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feistelBox[1][(t>>24)&0x3f]
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t = ((l << 28) | (l >> 4)) ^ uint32(k1)
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r ^= feistelBox[6][(t)&0x3f] ^
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feistelBox[4][(t>>8)&0x3f] ^
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feistelBox[2][(t>>16)&0x3f] ^
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feistelBox[0][(t>>24)&0x3f]
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return l, r
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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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var feistelBoxOnce sync.Once
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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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bit := (src >> n) & 1
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block |= bit << uint((len(permutation)-1)-position)
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}
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return
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}
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func initFeistelBox() {
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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(f, permutationFunction[:])
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// Row is determined by the 1st and 6th bit.
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// Column is the middle four bits.
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row := uint8(((i & 2) << 4) | i&1)
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col := uint8(j << 1)
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t := row | col
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// The rotation was performed in the feistel rounds, being factored out and now mixed into the feistelBox.
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f = (f << 1) | (f >> 31)
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feistelBox[s][t] = uint32(f)
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}
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}
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}
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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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out = make([]uint32, 16)
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last := in
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for i := 0; i < 16; i++ {
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// 28-bit circular left shift
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left := (last << (4 + ksRotations[i])) >> 4
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right := (last << 4) >> (32 - ksRotations[i])
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out[i] = left | right
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last = out[i]
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}
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return
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}
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// creates 16 56-bit subkeys from the original key
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func (c *desCipher) generateSubkeys(keyBytes []byte) {
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feistelBoxOnce.Do(initFeistelBox)
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// apply PC1 permutation to key
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key := binary.BigEndian.Uint64(keyBytes)
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permutedKey := permuteBlock(key, permutedChoice1[:])
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// rotate halves of permuted key according to the rotation schedule
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leftRotations := ksRotate(uint32(permutedKey >> 28))
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rightRotations := ksRotate(uint32(permutedKey<<4) >> 4)
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// generate subkeys
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for i := 0; i < 16; i++ {
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// combine halves to form 56-bit input to PC2
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pc2Input := uint64(leftRotations[i])<<28 | uint64(rightRotations[i])
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// apply PC2 permutation to 7 byte input
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c.subkeys[i] = unpack(permuteBlock(pc2Input, permutedChoice2[:]))
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}
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}
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// Expand 48-bit input to 64-bit, with each 6-bit block padded by extra two bits at the top.
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// By doing so, we can have the input blocks (four bits each), and the key blocks (six bits each) well-aligned without
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// extra shifts/rotations for alignments.
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func unpack(x uint64) uint64 {
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var result uint64
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result = ((x>>(6*1))&0xff)<<(8*0) |
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((x>>(6*3))&0xff)<<(8*1) |
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((x>>(6*5))&0xff)<<(8*2) |
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((x>>(6*7))&0xff)<<(8*3) |
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((x>>(6*0))&0xff)<<(8*4) |
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((x>>(6*2))&0xff)<<(8*5) |
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((x>>(6*4))&0xff)<<(8*6) |
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((x>>(6*6))&0xff)<<(8*7)
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return result
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}
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