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