| // 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) |
| |
| left = (left << 1) | (left >> 31) |
| right = (right << 1) | (right >> 31) |
| |
| if decrypt { |
| for i := 0; i < 8; i++ { |
| left, right = feistel(left, right, subkeys[15-2*i], subkeys[15-(2*i+1)]) |
| } |
| } else { |
| for i := 0; i < 8; i++ { |
| left, right = feistel(left, right, subkeys[2*i], subkeys[2*i+1]) |
| } |
| } |
| |
| left = (left << 31) | (left >> 1) |
| right = (right << 31) | (right >> 1) |
| |
| // 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(l, r uint32, k0, k1 uint64) (lout, rout uint32) { |
| var t uint32 |
| |
| t = r ^ uint32(k0>>32) |
| l ^= feistelBox[7][t&0x3f] ^ |
| feistelBox[5][(t>>8)&0x3f] ^ |
| feistelBox[3][(t>>16)&0x3f] ^ |
| feistelBox[1][(t>>24)&0x3f] |
| |
| t = ((r << 28) | (r >> 4)) ^ uint32(k0) |
| l ^= feistelBox[6][(t)&0x3f] ^ |
| feistelBox[4][(t>>8)&0x3f] ^ |
| feistelBox[2][(t>>16)&0x3f] ^ |
| feistelBox[0][(t>>24)&0x3f] |
| |
| t = l ^ uint32(k1>>32) |
| r ^= feistelBox[7][t&0x3f] ^ |
| feistelBox[5][(t>>8)&0x3f] ^ |
| feistelBox[3][(t>>16)&0x3f] ^ |
| feistelBox[1][(t>>24)&0x3f] |
| |
| t = ((l << 28) | (l >> 4)) ^ uint32(k1) |
| r ^= feistelBox[6][(t)&0x3f] ^ |
| feistelBox[4][(t>>8)&0x3f] ^ |
| feistelBox[2][(t>>16)&0x3f] ^ |
| feistelBox[0][(t>>24)&0x3f] |
| |
| return l, r |
| } |
| |
| // 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(f, permutationFunction[:]) |
| |
| // Row is determined by the 1st and 6th bit. |
| // Column is the middle four bits. |
| row := uint8(((i & 2) << 4) | i&1) |
| col := uint8(j << 1) |
| t := row | col |
| |
| // The rotation was performed in the feistel rounds, being factored out and now mixed into the feistelBox. |
| f = (f << 1) | (f >> 31) |
| |
| feistelBox[s][t] = uint32(f) |
| } |
| } |
| } |
| } |
| |
| // 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] = unpack(permuteBlock(pc2Input, permutedChoice2[:])) |
| } |
| } |
| |
| // Expand 48-bit input to 64-bit, with each 6-bit block padded by extra two bits at the top. |
| // By doing so, we can have the input blocks (four bits each), and the key blocks (six bits each) well-aligned without |
| // extra shifts/rotations for alignments. |
| func unpack(x uint64) uint64 { |
| var result uint64 |
| |
| result = ((x>>(6*1))&0xff)<<(8*0) | |
| ((x>>(6*3))&0xff)<<(8*1) | |
| ((x>>(6*5))&0xff)<<(8*2) | |
| ((x>>(6*7))&0xff)<<(8*3) | |
| ((x>>(6*0))&0xff)<<(8*4) | |
| ((x>>(6*2))&0xff)<<(8*5) | |
| ((x>>(6*4))&0xff)<<(8*6) | |
| ((x>>(6*6))&0xff)<<(8*7) |
| |
| return result |
| } |
