1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
|
// 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"
"sync"
)
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. feistelBox must be initialized via
// feistelBoxOnce.Do(initFeistelBox) first.
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
var feistelBoxOnce sync.Once
// 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 initFeistelBox() {
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 b6, 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) {
feistelBoxOnce.Do(initFeistelBox)
// 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
}
|
