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 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 */
rijndaelKeySetupDec(u32 rk[],const u8 cipherKey[])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
aes_decrypt_init(const u8 * key,size_t len)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
rijndaelDecrypt(const u32 rk[],const u8 ct[16],u8 pt[16])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
aes_decrypt(void * ctx,const u8 * crypt,u8 * plain)135 void aes_decrypt(void *ctx, const u8 *crypt, u8 *plain)
136 {
137 rijndaelDecrypt(ctx, crypt, plain);
138 }
139
140
aes_decrypt_deinit(void * ctx)141 void aes_decrypt_deinit(void *ctx)
142 {
143 os_memset(ctx, 0, AES_PRIV_SIZE);
144 os_free(ctx);
145 }
146