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 */
rijndaelKeySetupDec(u32 rk[],const u8 cipherKey[],int keyBits)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
aes_decrypt_init(const u8 * key,size_t len)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
rijndaelDecrypt(const u32 rk[],int Nr,const u8 ct[16],u8 pt[16])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
aes_decrypt(void * ctx,const u8 * crypt,u8 * plain)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
aes_decrypt_deinit(void * ctx)159 void aes_decrypt_deinit(void *ctx)
160 {
161 os_memset(ctx, 0, AES_PRIV_SIZE);
162 os_free(ctx);
163 }
164