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// Copyright 2011 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 des
import (
"encoding/binary"
)
func cryptBlock(subkeys []uint64, dst, src []byte, decrypt bool) {
b := binary.BigEndian.Uint64(src)
b = permuteInitialBlock(b)
left, right := uint32(b>>32), uint32(b)
var subkey uint64
for i := 0; i < 16; i++ {
if decrypt {
subkey = subkeys[15-i]
} else {
subkey = subkeys[i]
}
left, right = right, left^feistel(right, subkey)
}
// switch left & right and perform final permutation
preOutput := (uint64(right) << 32) | uint64(left)
binary.BigEndian.PutUint64(dst, permuteFinalBlock(preOutput))
}
// Encrypt one block from src into dst, using the subkeys.
func encryptBlock(subkeys []uint64, dst, src []byte) {
cryptBlock(subkeys, dst, src, false)
}
// Decrypt one block from src into dst, using the subkeys.
func decryptBlock(subkeys []uint64, dst, src []byte) {
cryptBlock(subkeys, dst, src, true)
}
// DES Feistel function
func feistel(right uint32, key uint64) (result uint32) {
sBoxLocations := key ^ expandBlock(right)
var sBoxResult uint32
for i := uint8(0); i < 8; i++ {
sBoxLocation := uint8(sBoxLocations>>42) & 0x3f
sBoxLocations <<= 6
// row determined by 1st and 6th bit
// column is middle four bits
row := (sBoxLocation & 0x1) | ((sBoxLocation & 0x20) >> 4)
column := (sBoxLocation >> 1) & 0xf
sBoxResult ^= feistelBox[i][16*row+column]
}
return sBoxResult
}
// feistelBox[s][16*i+j] contains the output of permutationFunction
// for sBoxes[s][i][j] << 4*(7-s)
var feistelBox [8][64]uint32
// general purpose function to perform DES block permutations
func permuteBlock(src uint64, permutation []uint8) (block uint64) {
for position, n := range permutation {
bit := (src >> n) & 1
block |= bit << uint((len(permutation)-1)-position)
}
return
}
func init() {
for s := range sBoxes {
for i := 0; i < 4; i++ {
for j := 0; j < 16; j++ {
f := uint64(sBoxes[s][i][j]) << (4 * (7 - uint(s)))
f = permuteBlock(uint64(f), permutationFunction[:])
feistelBox[s][16*i+j] = uint32(f)
}
}
}
}
// expandBlock expands an input block of 32 bits,
// producing an output block of 48 bits.
func expandBlock(src uint32) (block uint64) {
// rotate the 5 highest bits to the right.
src = (src << 5) | (src >> 27)
for i := 0; i < 8; i++ {
block <<= 6
// take the 6 bits on the right
block |= uint64(src) & (1<<6 - 1)
// advance by 4 bits.
src = (src << 4) | (src >> 28)
}
return
}
// permuteInitialBlock is equivalent to the permutation defined
// by initialPermutation.
func permuteInitialBlock(block uint64) uint64 {
// block = b7 b6 b5 b4 b3 b2 b1 b0 (8 bytes)
b1 := block >> 48
b2 := block << 48
block ^= b1 ^ b2 ^ b1<<48 ^ b2>>48
// block = b1 b0 b5 b4 b3 b2 b7 b6
b1 = block >> 32 & 0xff00ff
b2 = (block & 0xff00ff00)
block ^= b1<<32 ^ b2 ^ b1<<8 ^ b2<<24 // exchange b0 b4 with b3 b7
// block is now b1 b3 b5 b7 b0 b2 b4 b7, the permutation:
// ... 8
// ... 24
// ... 40
// ... 56
// 7 6 5 4 3 2 1 0
// 23 22 21 20 19 18 17 16
// ... 32
// ... 48
// exchange 4,5,6,7 with 32,33,34,35 etc.
b1 = block & 0x0f0f00000f0f0000
b2 = block & 0x0000f0f00000f0f0
block ^= b1 ^ b2 ^ b1>>12 ^ b2<<12
// block is the permutation:
//
// [+8] [+40]
//
// 7 6 5 4
// 23 22 21 20
// 3 2 1 0
// 19 18 17 16 [+32]
// exchange 0,1,4,5 with 18,19,22,23
b1 = block & 0x3300330033003300
b2 = block & 0x00cc00cc00cc00cc
block ^= b1 ^ b2 ^ b1>>6 ^ b2<<6
// block is the permutation:
// 15 14
// 13 12
// 11 10
// 9 8
// 7 6
// 5 4
// 3 2
// 1 0 [+16] [+32] [+64]
// exchange 0,2,4,6 with 9,11,13,15:
b1 = block & 0xaaaaaaaa55555555
block ^= b1 ^ b1>>33 ^ b1<<33
// block is the permutation:
// 6 14 22 30 38 46 54 62
// 4 12 20 28 36 44 52 60
// 2 10 18 26 34 42 50 58
// 0 8 16 24 32 40 48 56
// 7 15 23 31 39 47 55 63
// 5 13 21 29 37 45 53 61
// 3 11 19 27 35 43 51 59
// 1 9 17 25 33 41 49 57
return block
}
// permuteInitialBlock is equivalent to the permutation defined
// by finalPermutation.
func permuteFinalBlock(block uint64) uint64 {
// Perform the same bit exchanges as permuteInitialBlock
// but in reverse order.
b1 := block & 0xaaaaaaaa55555555
block ^= b1 ^ b1>>33 ^ b1<<33
b1 = block & 0x3300330033003300
b2 := block & 0x00cc00cc00cc00cc
block ^= b1 ^ b2 ^ b1>>6 ^ b2<<6
b1 = block & 0x0f0f00000f0f0000
b2 = block & 0x0000f0f00000f0f0
block ^= b1 ^ b2 ^ b1>>12 ^ b2<<12
b1 = block >> 32 & 0xff00ff
b2 = (block & 0xff00ff00)
block ^= b1<<32 ^ b2 ^ b1<<8 ^ b2<<24
b1 = block >> 48
b2 = block << 48
block ^= b1 ^ b2 ^ b1<<48 ^ b2>>48
return block
}
// creates 16 28-bit blocks rotated according
// to the rotation schedule
func ksRotate(in uint32) (out []uint32) {
out = make([]uint32, 16)
last := in
for i := 0; i < 16; i++ {
// 28-bit circular left shift
left := (last << (4 + ksRotations[i])) >> 4
right := (last << 4) >> (32 - ksRotations[i])
out[i] = left | right
last = out[i]
}
return
}
// creates 16 56-bit subkeys from the original key
func (c *desCipher) generateSubkeys(keyBytes []byte) {
// apply PC1 permutation to key
key := binary.BigEndian.Uint64(keyBytes)
permutedKey := permuteBlock(key, permutedChoice1[:])
// rotate halves of permuted key according to the rotation schedule
leftRotations := ksRotate(uint32(permutedKey >> 28))
rightRotations := ksRotate(uint32(permutedKey<<4) >> 4)
// generate subkeys
for i := 0; i < 16; i++ {
// combine halves to form 56-bit input to PC2
pc2Input := uint64(leftRotations[i])<<28 | uint64(rightRotations[i])
// apply PC2 permutation to 7 byte input
c.subkeys[i] = permuteBlock(pc2Input, permutedChoice2[:])
}
}
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