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@w1.fi> 13 * 14 * This program is free software; you can redistribute it and/or modify 15 * it under the terms of the GNU General Public License version 2 as 16 * published by the Free Software Foundation. 17 * 18 * Alternatively, this software may be distributed under the terms of BSD 19 * license. 20 * 21 * See README and COPYING for more details. 22 */ 23 24 #include "includes.h" 25 26 #include "common.h" 27 #include "crypto.h" 28 #include "aes_i.h" 29 30 /** 31 * Expand the cipher key into the decryption key schedule. 32 * 33 * @return the number of rounds for the given cipher key size. 34 */ 35 void rijndaelKeySetupDec(u32 rk[/*44*/], const u8 cipherKey[]) 36 { 37 int Nr = 10, i, j; 38 u32 temp; 39 40 /* expand the cipher key: */ 41 rijndaelKeySetupEnc(rk, cipherKey); 42 /* invert the order of the round keys: */ 43 for (i = 0, j = 4*Nr; i < j; i += 4, j -= 4) { 44 temp = rk[i ]; rk[i ] = rk[j ]; rk[j ] = temp; 45 temp = rk[i + 1]; rk[i + 1] = rk[j + 1]; rk[j + 1] = temp; 46 temp = rk[i + 2]; rk[i + 2] = rk[j + 2]; rk[j + 2] = temp; 47 temp = rk[i + 3]; rk[i + 3] = rk[j + 3]; rk[j + 3] = temp; 48 } 49 /* apply the inverse MixColumn transform to all round keys but the 50 * first and the last: */ 51 for (i = 1; i < Nr; i++) { 52 rk += 4; 53 for (j = 0; j < 4; j++) { 54 rk[j] = TD0_(TE4((rk[j] >> 24) )) ^ 55 TD1_(TE4((rk[j] >> 16) & 0xff)) ^ 56 TD2_(TE4((rk[j] >> 8) & 0xff)) ^ 57 TD3_(TE4((rk[j] ) & 0xff)); 58 } 59 } 60 } 61 62 void * aes_decrypt_init(const u8 *key, size_t len) 63 { 64 u32 *rk; 65 if (len != 16) 66 return NULL; 67 rk = os_malloc(AES_PRIV_SIZE); 68 if (rk == NULL) 69 return NULL; 70 rijndaelKeySetupDec(rk, key); 71 return rk; 72 } 73 74 static void rijndaelDecrypt(const u32 rk[/*44*/], const u8 ct[16], u8 pt[16]) 75 { 76 u32 s0, s1, s2, s3, t0, t1, t2, t3; 77 const int Nr = 10; 78 #ifndef FULL_UNROLL 79 int r; 80 #endif /* ?FULL_UNROLL */ 81 82 /* 83 * map byte array block to cipher state 84 * and add initial round key: 85 */ 86 s0 = GETU32(ct ) ^ rk[0]; 87 s1 = GETU32(ct + 4) ^ rk[1]; 88 s2 = GETU32(ct + 8) ^ rk[2]; 89 s3 = GETU32(ct + 12) ^ rk[3]; 90 91 #define ROUND(i,d,s) \ 92 d##0 = TD0(s##0) ^ TD1(s##3) ^ TD2(s##2) ^ TD3(s##1) ^ rk[4 * i]; \ 93 d##1 = TD0(s##1) ^ TD1(s##0) ^ TD2(s##3) ^ TD3(s##2) ^ rk[4 * i + 1]; \ 94 d##2 = TD0(s##2) ^ TD1(s##1) ^ TD2(s##0) ^ TD3(s##3) ^ rk[4 * i + 2]; \ 95 d##3 = TD0(s##3) ^ TD1(s##2) ^ TD2(s##1) ^ TD3(s##0) ^ rk[4 * i + 3] 96 97 #ifdef FULL_UNROLL 98 99 ROUND(1,t,s); 100 ROUND(2,s,t); 101 ROUND(3,t,s); 102 ROUND(4,s,t); 103 ROUND(5,t,s); 104 ROUND(6,s,t); 105 ROUND(7,t,s); 106 ROUND(8,s,t); 107 ROUND(9,t,s); 108 109 rk += Nr << 2; 110 111 #else /* !FULL_UNROLL */ 112 113 /* Nr - 1 full rounds: */ 114 r = Nr >> 1; 115 for (;;) { 116 ROUND(1,t,s); 117 rk += 8; 118 if (--r == 0) 119 break; 120 ROUND(0,s,t); 121 } 122 123 #endif /* ?FULL_UNROLL */ 124 125 #undef ROUND 126 127 /* 128 * apply last round and 129 * map cipher state to byte array block: 130 */ 131 s0 = TD41(t0) ^ TD42(t3) ^ TD43(t2) ^ TD44(t1) ^ rk[0]; 132 PUTU32(pt , s0); 133 s1 = TD41(t1) ^ TD42(t0) ^ TD43(t3) ^ TD44(t2) ^ rk[1]; 134 PUTU32(pt + 4, s1); 135 s2 = TD41(t2) ^ TD42(t1) ^ TD43(t0) ^ TD44(t3) ^ rk[2]; 136 PUTU32(pt + 8, s2); 137 s3 = TD41(t3) ^ TD42(t2) ^ TD43(t1) ^ TD44(t0) ^ rk[3]; 138 PUTU32(pt + 12, s3); 139 } 140 141 void aes_decrypt(void *ctx, const u8 *crypt, u8 *plain) 142 { 143 rijndaelDecrypt(ctx, crypt, plain); 144 } 145 146 147 void aes_decrypt_deinit(void *ctx) 148 { 149 os_memset(ctx, 0, AES_PRIV_SIZE); 150 os_free(ctx); 151 } 152