1 /* 2 * AES (Rijndael) cipher - decrypt 3 * 4 * Modifications to public domain implementation: 5 * - support only 128-bit keys 6 * - cleanup 7 * - use C pre-processor to make it easier to change S table access 8 * - added option (AES_SMALL_TABLES) for reducing code size by about 8 kB at 9 * cost of reduced throughput (quite small difference on Pentium 4, 10 * 10-25% when using -O1 or -O2 optimization) 11 * 12 * Copyright (c) 2003-2005, Jouni Malinen <j (at) w1.fi> 13 * 14 * This software may be distributed under the terms of the BSD license. 15 * See README for more details. 16 */ 17 18 #include "includes.h" 19 20 #include "common.h" 21 #include "crypto.h" 22 #include "aes_i.h" 23 24 /** 25 * Expand the cipher key into the decryption key schedule. 26 * 27 * @return the number of rounds for the given cipher key size. 28 */ 29 static void rijndaelKeySetupDec(u32 rk[/*44*/], const u8 cipherKey[]) 30 { 31 int Nr = 10, i, j; 32 u32 temp; 33 34 /* expand the cipher key: */ 35 rijndaelKeySetupEnc(rk, cipherKey); 36 /* invert the order of the round keys: */ 37 for (i = 0, j = 4*Nr; i < j; i += 4, j -= 4) { 38 temp = rk[i ]; rk[i ] = rk[j ]; rk[j ] = temp; 39 temp = rk[i + 1]; rk[i + 1] = rk[j + 1]; rk[j + 1] = temp; 40 temp = rk[i + 2]; rk[i + 2] = rk[j + 2]; rk[j + 2] = temp; 41 temp = rk[i + 3]; rk[i + 3] = rk[j + 3]; rk[j + 3] = temp; 42 } 43 /* apply the inverse MixColumn transform to all round keys but the 44 * first and the last: */ 45 for (i = 1; i < Nr; i++) { 46 rk += 4; 47 for (j = 0; j < 4; j++) { 48 rk[j] = TD0_(TE4((rk[j] >> 24) )) ^ 49 TD1_(TE4((rk[j] >> 16) & 0xff)) ^ 50 TD2_(TE4((rk[j] >> 8) & 0xff)) ^ 51 TD3_(TE4((rk[j] ) & 0xff)); 52 } 53 } 54 } 55 56 void * aes_decrypt_init(const u8 *key, size_t len) 57 { 58 u32 *rk; 59 if (len != 16) 60 return NULL; 61 rk = os_malloc(AES_PRIV_SIZE); 62 if (rk == NULL) 63 return NULL; 64 rijndaelKeySetupDec(rk, key); 65 return rk; 66 } 67 68 static void rijndaelDecrypt(const u32 rk[/*44*/], const u8 ct[16], u8 pt[16]) 69 { 70 u32 s0, s1, s2, s3, t0, t1, t2, t3; 71 const int Nr = 10; 72 #ifndef FULL_UNROLL 73 int r; 74 #endif /* ?FULL_UNROLL */ 75 76 /* 77 * map byte array block to cipher state 78 * and add initial round key: 79 */ 80 s0 = GETU32(ct ) ^ rk[0]; 81 s1 = GETU32(ct + 4) ^ rk[1]; 82 s2 = GETU32(ct + 8) ^ rk[2]; 83 s3 = GETU32(ct + 12) ^ rk[3]; 84 85 #define ROUND(i,d,s) \ 86 d##0 = TD0(s##0) ^ TD1(s##3) ^ TD2(s##2) ^ TD3(s##1) ^ rk[4 * i]; \ 87 d##1 = TD0(s##1) ^ TD1(s##0) ^ TD2(s##3) ^ TD3(s##2) ^ rk[4 * i + 1]; \ 88 d##2 = TD0(s##2) ^ TD1(s##1) ^ TD2(s##0) ^ TD3(s##3) ^ rk[4 * i + 2]; \ 89 d##3 = TD0(s##3) ^ TD1(s##2) ^ TD2(s##1) ^ TD3(s##0) ^ rk[4 * i + 3] 90 91 #ifdef FULL_UNROLL 92 93 ROUND(1,t,s); 94 ROUND(2,s,t); 95 ROUND(3,t,s); 96 ROUND(4,s,t); 97 ROUND(5,t,s); 98 ROUND(6,s,t); 99 ROUND(7,t,s); 100 ROUND(8,s,t); 101 ROUND(9,t,s); 102 103 rk += Nr << 2; 104 105 #else /* !FULL_UNROLL */ 106 107 /* Nr - 1 full rounds: */ 108 r = Nr >> 1; 109 for (;;) { 110 ROUND(1,t,s); 111 rk += 8; 112 if (--r == 0) 113 break; 114 ROUND(0,s,t); 115 } 116 117 #endif /* ?FULL_UNROLL */ 118 119 #undef ROUND 120 121 /* 122 * apply last round and 123 * map cipher state to byte array block: 124 */ 125 s0 = TD41(t0) ^ TD42(t3) ^ TD43(t2) ^ TD44(t1) ^ rk[0]; 126 PUTU32(pt , s0); 127 s1 = TD41(t1) ^ TD42(t0) ^ TD43(t3) ^ TD44(t2) ^ rk[1]; 128 PUTU32(pt + 4, s1); 129 s2 = TD41(t2) ^ TD42(t1) ^ TD43(t0) ^ TD44(t3) ^ rk[2]; 130 PUTU32(pt + 8, s2); 131 s3 = TD41(t3) ^ TD42(t2) ^ TD43(t1) ^ TD44(t0) ^ rk[3]; 132 PUTU32(pt + 12, s3); 133 } 134 135 void aes_decrypt(void *ctx, const u8 *crypt, u8 *plain) 136 { 137 rijndaelDecrypt(ctx, crypt, plain); 138 } 139 140 141 void aes_decrypt_deinit(void *ctx) 142 { 143 os_memset(ctx, 0, AES_PRIV_SIZE); 144 os_free(ctx); 145 } 146
