1 /* 2 * AES (Rijndael) cipher - decrypt 3 * 4 * Modifications to public domain implementation: 5 * - cleanup 6 * - use C pre-processor to make it easier to change S table access 7 * - added option (AES_SMALL_TABLES) for reducing code size by about 8 kB at 8 * cost of reduced throughput (quite small difference on Pentium 4, 9 * 10-25% when using -O1 or -O2 optimization) 10 * 11 * Copyright (c) 2003-2012, Jouni Malinen <j@w1.fi> 12 * 13 * This software may be distributed under the terms of the BSD license. 14 * See README for more details. 15 */ 16 17 #include "includes.h" 18 19 #include "common.h" 20 #include "crypto.h" 21 #include "aes_i.h" 22 23 /** 24 * Expand the cipher key into the decryption key schedule. 25 * 26 * @return the number of rounds for the given cipher key size. 27 */ 28 static int rijndaelKeySetupDec(u32 rk[], const u8 cipherKey[], int keyBits) 29 { 30 int Nr, i, j; 31 u32 temp; 32 33 /* expand the cipher key: */ 34 Nr = rijndaelKeySetupEnc(rk, cipherKey, keyBits); 35 if (Nr < 0) 36 return Nr; 37 /* invert the order of the round keys: */ 38 for (i = 0, j = 4*Nr; i < j; i += 4, j -= 4) { 39 temp = rk[i ]; rk[i ] = rk[j ]; rk[j ] = temp; 40 temp = rk[i + 1]; rk[i + 1] = rk[j + 1]; rk[j + 1] = temp; 41 temp = rk[i + 2]; rk[i + 2] = rk[j + 2]; rk[j + 2] = temp; 42 temp = rk[i + 3]; rk[i + 3] = rk[j + 3]; rk[j + 3] = temp; 43 } 44 /* apply the inverse MixColumn transform to all round keys but the 45 * first and the last: */ 46 for (i = 1; i < Nr; i++) { 47 rk += 4; 48 for (j = 0; j < 4; j++) { 49 rk[j] = TD0_(TE4((rk[j] >> 24) )) ^ 50 TD1_(TE4((rk[j] >> 16) & 0xff)) ^ 51 TD2_(TE4((rk[j] >> 8) & 0xff)) ^ 52 TD3_(TE4((rk[j] ) & 0xff)); 53 } 54 } 55 56 return Nr; 57 } 58 59 void * aes_decrypt_init(const u8 *key, size_t len) 60 { 61 u32 *rk; 62 int res; 63 rk = os_malloc(AES_PRIV_SIZE); 64 if (rk == NULL) 65 return NULL; 66 res = rijndaelKeySetupDec(rk, key, len * 8); 67 if (res < 0) { 68 os_free(rk); 69 return NULL; 70 } 71 rk[AES_PRIV_NR_POS] = res; 72 return rk; 73 } 74 75 static void rijndaelDecrypt(const u32 rk[/*44*/], int Nr, const u8 ct[16], 76 u8 pt[16]) 77 { 78 u32 s0, s1, s2, s3, t0, t1, t2, t3; 79 #ifndef FULL_UNROLL 80 int r; 81 #endif /* ?FULL_UNROLL */ 82 83 /* 84 * map byte array block to cipher state 85 * and add initial round key: 86 */ 87 s0 = GETU32(ct ) ^ rk[0]; 88 s1 = GETU32(ct + 4) ^ rk[1]; 89 s2 = GETU32(ct + 8) ^ rk[2]; 90 s3 = GETU32(ct + 12) ^ rk[3]; 91 92 #define ROUND(i,d,s) \ 93 d##0 = TD0(s##0) ^ TD1(s##3) ^ TD2(s##2) ^ TD3(s##1) ^ rk[4 * i]; \ 94 d##1 = TD0(s##1) ^ TD1(s##0) ^ TD2(s##3) ^ TD3(s##2) ^ rk[4 * i + 1]; \ 95 d##2 = TD0(s##2) ^ TD1(s##1) ^ TD2(s##0) ^ TD3(s##3) ^ rk[4 * i + 2]; \ 96 d##3 = TD0(s##3) ^ TD1(s##2) ^ TD2(s##1) ^ TD3(s##0) ^ rk[4 * i + 3] 97 98 #ifdef FULL_UNROLL 99 100 ROUND(1,t,s); 101 ROUND(2,s,t); 102 ROUND(3,t,s); 103 ROUND(4,s,t); 104 ROUND(5,t,s); 105 ROUND(6,s,t); 106 ROUND(7,t,s); 107 ROUND(8,s,t); 108 ROUND(9,t,s); 109 if (Nr > 10) { 110 ROUND(10,s,t); 111 ROUND(11,t,s); 112 if (Nr > 12) { 113 ROUND(12,s,t); 114 ROUND(13,t,s); 115 } 116 } 117 118 rk += Nr << 2; 119 120 #else /* !FULL_UNROLL */ 121 122 /* Nr - 1 full rounds: */ 123 r = Nr >> 1; 124 for (;;) { 125 ROUND(1,t,s); 126 rk += 8; 127 if (--r == 0) 128 break; 129 ROUND(0,s,t); 130 } 131 132 #endif /* ?FULL_UNROLL */ 133 134 #undef ROUND 135 136 /* 137 * apply last round and 138 * map cipher state to byte array block: 139 */ 140 s0 = TD41(t0) ^ TD42(t3) ^ TD43(t2) ^ TD44(t1) ^ rk[0]; 141 PUTU32(pt , s0); 142 s1 = TD41(t1) ^ TD42(t0) ^ TD43(t3) ^ TD44(t2) ^ rk[1]; 143 PUTU32(pt + 4, s1); 144 s2 = TD41(t2) ^ TD42(t1) ^ TD43(t0) ^ TD44(t3) ^ rk[2]; 145 PUTU32(pt + 8, s2); 146 s3 = TD41(t3) ^ TD42(t2) ^ TD43(t1) ^ TD44(t0) ^ rk[3]; 147 PUTU32(pt + 12, s3); 148 } 149 150 151 int aes_decrypt(void *ctx, const u8 *crypt, u8 *plain) 152 { 153 u32 *rk = ctx; 154 rijndaelDecrypt(ctx, rk[AES_PRIV_NR_POS], crypt, plain); 155 return 0; 156 } 157 158 159 void aes_decrypt_deinit(void *ctx) 160 { 161 os_memset(ctx, 0, AES_PRIV_SIZE); 162 os_free(ctx); 163 } 164