2 * AES (Rijndael) cipher - decrypt
4 * Modifications to public domain implementation:
5 * - support only 128-bit keys
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)
12 * Copyright (c) 2003-2005, Jouni Malinen <j@w1.fi>
14 * This software may be distributed under the terms of the BSD license.
15 * See README for more details.
25 * Expand the cipher key into the decryption key schedule.
27 * @return the number of rounds for the given cipher key size.
29 static void rijndaelKeySetupDec(u32 rk[/*44*/], const u8 cipherKey[])
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;
43 /* apply the inverse MixColumn transform to all round keys but the
44 * first and the last: */
45 for (i = 1; i < Nr; i++) {
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));
56 void * aes_decrypt_init(const u8 *key, size_t len)
61 rk = os_malloc(AES_PRIV_SIZE);
64 rijndaelKeySetupDec(rk, key);
68 static void rijndaelDecrypt(const u32 rk[/*44*/], const u8 ct[16], u8 pt[16])
70 u32 s0, s1, s2, s3, t0, t1, t2, t3;
74 #endif /* ?FULL_UNROLL */
77 * map byte array block to cipher state
78 * and add initial round key:
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];
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]
105 #else /* !FULL_UNROLL */
107 /* Nr - 1 full rounds: */
117 #endif /* ?FULL_UNROLL */
122 * apply last round and
123 * map cipher state to byte array block:
125 s0 = TD41(t0) ^ TD42(t3) ^ TD43(t2) ^ TD44(t1) ^ rk[0];
127 s1 = TD41(t1) ^ TD42(t0) ^ TD43(t3) ^ TD44(t2) ^ rk[1];
129 s2 = TD41(t2) ^ TD42(t1) ^ TD43(t0) ^ TD44(t3) ^ rk[2];
131 s3 = TD41(t3) ^ TD42(t2) ^ TD43(t1) ^ TD44(t0) ^ rk[3];
135 void aes_decrypt(void *ctx, const u8 *crypt, u8 *plain)
137 rijndaelDecrypt(ctx, crypt, plain);
141 void aes_decrypt_deinit(void *ctx)
143 os_memset(ctx, 0, AES_PRIV_SIZE);