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 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 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 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 115 rotr16(uint32_t x) 116 { 117 return (x << 16) | (x >> 16); 118 } 119 120 static void 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 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