1// Copyright 2011 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package des
6
7import (
8	"internal/byteorder"
9	"sync"
10)
11
12func cryptBlock(subkeys []uint64, dst, src []byte, decrypt bool) {
13	b := byteorder.BeUint64(src)
14	b = permuteInitialBlock(b)
15	left, right := uint32(b>>32), uint32(b)
16
17	left = (left << 1) | (left >> 31)
18	right = (right << 1) | (right >> 31)
19
20	if decrypt {
21		for i := 0; i < 8; i++ {
22			left, right = feistel(left, right, subkeys[15-2*i], subkeys[15-(2*i+1)])
23		}
24	} else {
25		for i := 0; i < 8; i++ {
26			left, right = feistel(left, right, subkeys[2*i], subkeys[2*i+1])
27		}
28	}
29
30	left = (left << 31) | (left >> 1)
31	right = (right << 31) | (right >> 1)
32
33	// switch left & right and perform final permutation
34	preOutput := (uint64(right) << 32) | uint64(left)
35	byteorder.BePutUint64(dst, permuteFinalBlock(preOutput))
36}
37
38// DES Feistel function. feistelBox must be initialized via
39// feistelBoxOnce.Do(initFeistelBox) first.
40func feistel(l, r uint32, k0, k1 uint64) (lout, rout uint32) {
41	var t uint32
42
43	t = r ^ uint32(k0>>32)
44	l ^= feistelBox[7][t&0x3f] ^
45		feistelBox[5][(t>>8)&0x3f] ^
46		feistelBox[3][(t>>16)&0x3f] ^
47		feistelBox[1][(t>>24)&0x3f]
48
49	t = ((r << 28) | (r >> 4)) ^ uint32(k0)
50	l ^= feistelBox[6][(t)&0x3f] ^
51		feistelBox[4][(t>>8)&0x3f] ^
52		feistelBox[2][(t>>16)&0x3f] ^
53		feistelBox[0][(t>>24)&0x3f]
54
55	t = l ^ uint32(k1>>32)
56	r ^= feistelBox[7][t&0x3f] ^
57		feistelBox[5][(t>>8)&0x3f] ^
58		feistelBox[3][(t>>16)&0x3f] ^
59		feistelBox[1][(t>>24)&0x3f]
60
61	t = ((l << 28) | (l >> 4)) ^ uint32(k1)
62	r ^= feistelBox[6][(t)&0x3f] ^
63		feistelBox[4][(t>>8)&0x3f] ^
64		feistelBox[2][(t>>16)&0x3f] ^
65		feistelBox[0][(t>>24)&0x3f]
66
67	return l, r
68}
69
70// feistelBox[s][16*i+j] contains the output of permutationFunction
71// for sBoxes[s][i][j] << 4*(7-s)
72var feistelBox [8][64]uint32
73
74var feistelBoxOnce sync.Once
75
76// general purpose function to perform DES block permutations.
77func permuteBlock(src uint64, permutation []uint8) (block uint64) {
78	for position, n := range permutation {
79		bit := (src >> n) & 1
80		block |= bit << uint((len(permutation)-1)-position)
81	}
82	return
83}
84
85func initFeistelBox() {
86	for s := range sBoxes {
87		for i := 0; i < 4; i++ {
88			for j := 0; j < 16; j++ {
89				f := uint64(sBoxes[s][i][j]) << (4 * (7 - uint(s)))
90				f = permuteBlock(f, permutationFunction[:])
91
92				// Row is determined by the 1st and 6th bit.
93				// Column is the middle four bits.
94				row := uint8(((i & 2) << 4) | i&1)
95				col := uint8(j << 1)
96				t := row | col
97
98				// The rotation was performed in the feistel rounds, being factored out and now mixed into the feistelBox.
99				f = (f << 1) | (f >> 31)
100
101				feistelBox[s][t] = uint32(f)
102			}
103		}
104	}
105}
106
107// permuteInitialBlock is equivalent to the permutation defined
108// by initialPermutation.
109func permuteInitialBlock(block uint64) uint64 {
110	// block = b7 b6 b5 b4 b3 b2 b1 b0 (8 bytes)
111	b1 := block >> 48
112	b2 := block << 48
113	block ^= b1 ^ b2 ^ b1<<48 ^ b2>>48
114
115	// block = b1 b0 b5 b4 b3 b2 b7 b6
116	b1 = block >> 32 & 0xff00ff
117	b2 = (block & 0xff00ff00)
118	block ^= b1<<32 ^ b2 ^ b1<<8 ^ b2<<24 // exchange b0 b4 with b3 b7
119
120	// block is now b1 b3 b5 b7 b0 b2 b4 b6, the permutation:
121	//                  ...  8
122	//                  ... 24
123	//                  ... 40
124	//                  ... 56
125	//  7  6  5  4  3  2  1  0
126	// 23 22 21 20 19 18 17 16
127	//                  ... 32
128	//                  ... 48
129
130	// exchange 4,5,6,7 with 32,33,34,35 etc.
131	b1 = block & 0x0f0f00000f0f0000
132	b2 = block & 0x0000f0f00000f0f0
133	block ^= b1 ^ b2 ^ b1>>12 ^ b2<<12
134
135	// block is the permutation:
136	//
137	//   [+8]         [+40]
138	//
139	//  7  6  5  4
140	// 23 22 21 20
141	//  3  2  1  0
142	// 19 18 17 16    [+32]
143
144	// exchange 0,1,4,5 with 18,19,22,23
145	b1 = block & 0x3300330033003300
146	b2 = block & 0x00cc00cc00cc00cc
147	block ^= b1 ^ b2 ^ b1>>6 ^ b2<<6
148
149	// block is the permutation:
150	// 15 14
151	// 13 12
152	// 11 10
153	//  9  8
154	//  7  6
155	//  5  4
156	//  3  2
157	//  1  0 [+16] [+32] [+64]
158
159	// exchange 0,2,4,6 with 9,11,13,15:
160	b1 = block & 0xaaaaaaaa55555555
161	block ^= b1 ^ b1>>33 ^ b1<<33
162
163	// block is the permutation:
164	// 6 14 22 30 38 46 54 62
165	// 4 12 20 28 36 44 52 60
166	// 2 10 18 26 34 42 50 58
167	// 0  8 16 24 32 40 48 56
168	// 7 15 23 31 39 47 55 63
169	// 5 13 21 29 37 45 53 61
170	// 3 11 19 27 35 43 51 59
171	// 1  9 17 25 33 41 49 57
172	return block
173}
174
175// permuteFinalBlock is equivalent to the permutation defined
176// by finalPermutation.
177func permuteFinalBlock(block uint64) uint64 {
178	// Perform the same bit exchanges as permuteInitialBlock
179	// but in reverse order.
180	b1 := block & 0xaaaaaaaa55555555
181	block ^= b1 ^ b1>>33 ^ b1<<33
182
183	b1 = block & 0x3300330033003300
184	b2 := block & 0x00cc00cc00cc00cc
185	block ^= b1 ^ b2 ^ b1>>6 ^ b2<<6
186
187	b1 = block & 0x0f0f00000f0f0000
188	b2 = block & 0x0000f0f00000f0f0
189	block ^= b1 ^ b2 ^ b1>>12 ^ b2<<12
190
191	b1 = block >> 32 & 0xff00ff
192	b2 = (block & 0xff00ff00)
193	block ^= b1<<32 ^ b2 ^ b1<<8 ^ b2<<24
194
195	b1 = block >> 48
196	b2 = block << 48
197	block ^= b1 ^ b2 ^ b1<<48 ^ b2>>48
198	return block
199}
200
201// creates 16 28-bit blocks rotated according
202// to the rotation schedule.
203func ksRotate(in uint32) (out []uint32) {
204	out = make([]uint32, 16)
205	last := in
206	for i := 0; i < 16; i++ {
207		// 28-bit circular left shift
208		left := (last << (4 + ksRotations[i])) >> 4
209		right := (last << 4) >> (32 - ksRotations[i])
210		out[i] = left | right
211		last = out[i]
212	}
213	return
214}
215
216// creates 16 56-bit subkeys from the original key.
217func (c *desCipher) generateSubkeys(keyBytes []byte) {
218	feistelBoxOnce.Do(initFeistelBox)
219
220	// apply PC1 permutation to key
221	key := byteorder.BeUint64(keyBytes)
222	permutedKey := permuteBlock(key, permutedChoice1[:])
223
224	// rotate halves of permuted key according to the rotation schedule
225	leftRotations := ksRotate(uint32(permutedKey >> 28))
226	rightRotations := ksRotate(uint32(permutedKey<<4) >> 4)
227
228	// generate subkeys
229	for i := 0; i < 16; i++ {
230		// combine halves to form 56-bit input to PC2
231		pc2Input := uint64(leftRotations[i])<<28 | uint64(rightRotations[i])
232		// apply PC2 permutation to 7 byte input
233		c.subkeys[i] = unpack(permuteBlock(pc2Input, permutedChoice2[:]))
234	}
235}
236
237// Expand 48-bit input to 64-bit, with each 6-bit block padded by extra two bits at the top.
238// By doing so, we can have the input blocks (four bits each), and the key blocks (six bits each) well-aligned without
239// extra shifts/rotations for alignments.
240func unpack(x uint64) uint64 {
241	return ((x>>(6*1))&0xff)<<(8*0) |
242		((x>>(6*3))&0xff)<<(8*1) |
243		((x>>(6*5))&0xff)<<(8*2) |
244		((x>>(6*7))&0xff)<<(8*3) |
245		((x>>(6*0))&0xff)<<(8*4) |
246		((x>>(6*2))&0xff)<<(8*5) |
247		((x>>(6*4))&0xff)<<(8*6) |
248		((x>>(6*6))&0xff)<<(8*7)
249}
250