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      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 (at) 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  */
     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 
     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 
     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 void aes_decrypt(void *ctx, const u8 *crypt, u8 *plain)
    151 {
    152 	u32 *rk = ctx;
    153 	rijndaelDecrypt(ctx, rk[AES_PRIV_NR_POS], crypt, plain);
    154 }
    155 
    156 
    157 void aes_decrypt_deinit(void *ctx)
    158 {
    159 	os_memset(ctx, 0, AES_PRIV_SIZE);
    160 	os_free(ctx);
    161 }
    162