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      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 (at) 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  */
     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 
     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 
     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 
    135 void aes_decrypt(void *ctx, const u8 *crypt, u8 *plain)
    136 {
    137 	rijndaelDecrypt(ctx, crypt, plain);
    138 }
    139 
    140 
    141 void aes_decrypt_deinit(void *ctx)
    142 {
    143 	os_memset(ctx, 0, AES_PRIV_SIZE);
    144 	os_free(ctx);
    145 }
    146