1 /*
2 * Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
3 *
4 * Permission is hereby granted, free of charge, to any person obtaining
5 * a copy of this software and associated documentation files (the
6 * "Software"), to deal in the Software without restriction, including
7 * without limitation the rights to use, copy, modify, merge, publish,
8 * distribute, sublicense, and/or sell copies of the Software, and to
9 * permit persons to whom the Software is furnished to do so, subject to
10 * the following conditions:
11 *
12 * The above copyright notice and this permission notice shall be
13 * included in all copies or substantial portions of the Software.
14 *
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
16 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
17 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
18 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
19 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
20 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
21 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
22 * SOFTWARE.
23 */
24
25 #include "inner.h"
26
27 /* see inner.h */
28 void
br_aes_ct_bitslice_invSbox(uint32_t * q)29 br_aes_ct_bitslice_invSbox(uint32_t *q)
30 {
31 /*
32 * AES S-box is:
33 * S(x) = A(I(x)) ^ 0x63
34 * where I() is inversion in GF(256), and A() is a linear
35 * transform (0 is formally defined to be its own inverse).
36 * Since inversion is an involution, the inverse S-box can be
37 * computed from the S-box as:
38 * iS(x) = B(S(B(x ^ 0x63)) ^ 0x63)
39 * where B() is the inverse of A(). Indeed, for any y in GF(256):
40 * iS(S(y)) = B(A(I(B(A(I(y)) ^ 0x63 ^ 0x63))) ^ 0x63 ^ 0x63) = y
41 *
42 * Note: we reuse the implementation of the forward S-box,
43 * instead of duplicating it here, so that total code size is
44 * lower. By merging the B() transforms into the S-box circuit
45 * we could make faster CBC decryption, but CBC decryption is
46 * already quite faster than CBC encryption because we can
47 * process two blocks in parallel.
48 */
49 uint32_t q0, q1, q2, q3, q4, q5, q6, q7;
50
51 q0 = ~q[0];
52 q1 = ~q[1];
53 q2 = q[2];
54 q3 = q[3];
55 q4 = q[4];
56 q5 = ~q[5];
57 q6 = ~q[6];
58 q7 = q[7];
59 q[7] = q1 ^ q4 ^ q6;
60 q[6] = q0 ^ q3 ^ q5;
61 q[5] = q7 ^ q2 ^ q4;
62 q[4] = q6 ^ q1 ^ q3;
63 q[3] = q5 ^ q0 ^ q2;
64 q[2] = q4 ^ q7 ^ q1;
65 q[1] = q3 ^ q6 ^ q0;
66 q[0] = q2 ^ q5 ^ q7;
67
68 br_aes_ct_bitslice_Sbox(q);
69
70 q0 = ~q[0];
71 q1 = ~q[1];
72 q2 = q[2];
73 q3 = q[3];
74 q4 = q[4];
75 q5 = ~q[5];
76 q6 = ~q[6];
77 q7 = q[7];
78 q[7] = q1 ^ q4 ^ q6;
79 q[6] = q0 ^ q3 ^ q5;
80 q[5] = q7 ^ q2 ^ q4;
81 q[4] = q6 ^ q1 ^ q3;
82 q[3] = q5 ^ q0 ^ q2;
83 q[2] = q4 ^ q7 ^ q1;
84 q[1] = q3 ^ q6 ^ q0;
85 q[0] = q2 ^ q5 ^ q7;
86 }
87
88 static void
add_round_key(uint32_t * q,const uint32_t * sk)89 add_round_key(uint32_t *q, const uint32_t *sk)
90 {
91 int i;
92
93 for (i = 0; i < 8; i ++) {
94 q[i] ^= sk[i];
95 }
96 }
97
98 static void
inv_shift_rows(uint32_t * q)99 inv_shift_rows(uint32_t *q)
100 {
101 int i;
102
103 for (i = 0; i < 8; i ++) {
104 uint32_t x;
105
106 x = q[i];
107 q[i] = (x & 0x000000FF)
108 | ((x & 0x00003F00) << 2) | ((x & 0x0000C000) >> 6)
109 | ((x & 0x000F0000) << 4) | ((x & 0x00F00000) >> 4)
110 | ((x & 0x03000000) << 6) | ((x & 0xFC000000) >> 2);
111 }
112 }
113
114 static inline uint32_t
rotr16(uint32_t x)115 rotr16(uint32_t x)
116 {
117 return (x << 16) | (x >> 16);
118 }
119
120 static void
inv_mix_columns(uint32_t * q)121 inv_mix_columns(uint32_t *q)
122 {
123 uint32_t q0, q1, q2, q3, q4, q5, q6, q7;
124 uint32_t r0, r1, r2, r3, r4, r5, r6, r7;
125
126 q0 = q[0];
127 q1 = q[1];
128 q2 = q[2];
129 q3 = q[3];
130 q4 = q[4];
131 q5 = q[5];
132 q6 = q[6];
133 q7 = q[7];
134 r0 = (q0 >> 8) | (q0 << 24);
135 r1 = (q1 >> 8) | (q1 << 24);
136 r2 = (q2 >> 8) | (q2 << 24);
137 r3 = (q3 >> 8) | (q3 << 24);
138 r4 = (q4 >> 8) | (q4 << 24);
139 r5 = (q5 >> 8) | (q5 << 24);
140 r6 = (q6 >> 8) | (q6 << 24);
141 r7 = (q7 >> 8) | (q7 << 24);
142
143 q[0] = q5 ^ q6 ^ q7 ^ r0 ^ r5 ^ r7 ^ rotr16(q0 ^ q5 ^ q6 ^ r0 ^ r5);
144 q[1] = q0 ^ q5 ^ r0 ^ r1 ^ r5 ^ r6 ^ r7 ^ rotr16(q1 ^ q5 ^ q7 ^ r1 ^ r5 ^ r6);
145 q[2] = q0 ^ q1 ^ q6 ^ r1 ^ r2 ^ r6 ^ r7 ^ rotr16(q0 ^ q2 ^ q6 ^ r2 ^ r6 ^ r7);
146 q[3] = q0 ^ q1 ^ q2 ^ q5 ^ q6 ^ r0 ^ r2 ^ r3 ^ r5 ^ rotr16(q0 ^ q1 ^ q3 ^ q5 ^ q6 ^ q7 ^ r0 ^ r3 ^ r5 ^ r7);
147 q[4] = q1 ^ q2 ^ q3 ^ q5 ^ r1 ^ r3 ^ r4 ^ r5 ^ r6 ^ r7 ^ rotr16(q1 ^ q2 ^ q4 ^ q5 ^ q7 ^ r1 ^ r4 ^ r5 ^ r6);
148 q[5] = q2 ^ q3 ^ q4 ^ q6 ^ r2 ^ r4 ^ r5 ^ r6 ^ r7 ^ rotr16(q2 ^ q3 ^ q5 ^ q6 ^ r2 ^ r5 ^ r6 ^ r7);
149 q[6] = q3 ^ q4 ^ q5 ^ q7 ^ r3 ^ r5 ^ r6 ^ r7 ^ rotr16(q3 ^ q4 ^ q6 ^ q7 ^ r3 ^ r6 ^ r7);
150 q[7] = q4 ^ q5 ^ q6 ^ r4 ^ r6 ^ r7 ^ rotr16(q4 ^ q5 ^ q7 ^ r4 ^ r7);
151 }
152
153 /* see inner.h */
154 void
br_aes_ct_bitslice_decrypt(unsigned num_rounds,const uint32_t * skey,uint32_t * q)155 br_aes_ct_bitslice_decrypt(unsigned num_rounds,
156 const uint32_t *skey, uint32_t *q)
157 {
158 unsigned u;
159
160 add_round_key(q, skey + (num_rounds << 3));
161 for (u = num_rounds - 1; u > 0; u --) {
162 inv_shift_rows(q);
163 br_aes_ct_bitslice_invSbox(q);
164 add_round_key(q, skey + (u << 3));
165 inv_mix_columns(q);
166 }
167 inv_shift_rows(q);
168 br_aes_ct_bitslice_invSbox(q);
169 add_round_key(q, skey);
170 }
171