| // 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[:]) |
| } |
| } |