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/*
* AES (Rijndael) cipher - decrypt
*
* Modifications to public domain implementation:
* - support only 128-bit keys
* - cleanup
* - use C pre-processor to make it easier to change S table access
* - added option (AES_SMALL_TABLES) for reducing code size by about 8 kB at
* cost of reduced throughput (quite small difference on Pentium 4,
* 10-25% when using -O1 or -O2 optimization)
*
* Copyright (c) 2003-2005, Jouni Malinen <j@w1.fi>
*
* This software may be distributed under the terms of the BSD license.
* See README for more details.
*/
#include "includes.h"
#include "common.h"
#include "crypto.h"
#include "aes_i.h"
/**
* Expand the cipher key into the decryption key schedule.
*
* @return the number of rounds for the given cipher key size.
*/
static void rijndaelKeySetupDec(u32 rk[/*44*/], const u8 cipherKey[])
{
int Nr = 10, i, j;
u32 temp;
/* expand the cipher key: */
rijndaelKeySetupEnc(rk, cipherKey);
/* invert the order of the round keys: */
for (i = 0, j = 4*Nr; i < j; i += 4, j -= 4) {
temp = rk[i ]; rk[i ] = rk[j ]; rk[j ] = temp;
temp = rk[i + 1]; rk[i + 1] = rk[j + 1]; rk[j + 1] = temp;
temp = rk[i + 2]; rk[i + 2] = rk[j + 2]; rk[j + 2] = temp;
temp = rk[i + 3]; rk[i + 3] = rk[j + 3]; rk[j + 3] = temp;
}
/* apply the inverse MixColumn transform to all round keys but the
* first and the last: */
for (i = 1; i < Nr; i++) {
rk += 4;
for (j = 0; j < 4; j++) {
rk[j] = TD0_(TE4((rk[j] >> 24) )) ^
TD1_(TE4((rk[j] >> 16) & 0xff)) ^
TD2_(TE4((rk[j] >> 8) & 0xff)) ^
TD3_(TE4((rk[j] ) & 0xff));
}
}
}
void * aes_decrypt_init(const u8 *key, size_t len)
{
u32 *rk;
if (len != 16)
return NULL;
rk = os_malloc(AES_PRIV_SIZE);
if (rk == NULL)
return NULL;
rijndaelKeySetupDec(rk, key);
return rk;
}
static void rijndaelDecrypt(const u32 rk[/*44*/], const u8 ct[16], u8 pt[16])
{
u32 s0, s1, s2, s3, t0, t1, t2, t3;
const int Nr = 10;
#ifndef FULL_UNROLL
int r;
#endif /* ?FULL_UNROLL */
/*
* map byte array block to cipher state
* and add initial round key:
*/
s0 = GETU32(ct ) ^ rk[0];
s1 = GETU32(ct + 4) ^ rk[1];
s2 = GETU32(ct + 8) ^ rk[2];
s3 = GETU32(ct + 12) ^ rk[3];
#define ROUND(i,d,s) \
d##0 = TD0(s##0) ^ TD1(s##3) ^ TD2(s##2) ^ TD3(s##1) ^ rk[4 * i]; \
d##1 = TD0(s##1) ^ TD1(s##0) ^ TD2(s##3) ^ TD3(s##2) ^ rk[4 * i + 1]; \
d##2 = TD0(s##2) ^ TD1(s##1) ^ TD2(s##0) ^ TD3(s##3) ^ rk[4 * i + 2]; \
d##3 = TD0(s##3) ^ TD1(s##2) ^ TD2(s##1) ^ TD3(s##0) ^ rk[4 * i + 3]
#ifdef FULL_UNROLL
ROUND(1,t,s);
ROUND(2,s,t);
ROUND(3,t,s);
ROUND(4,s,t);
ROUND(5,t,s);
ROUND(6,s,t);
ROUND(7,t,s);
ROUND(8,s,t);
ROUND(9,t,s);
rk += Nr << 2;
#else /* !FULL_UNROLL */
/* Nr - 1 full rounds: */
r = Nr >> 1;
for (;;) {
ROUND(1,t,s);
rk += 8;
if (--r == 0)
break;
ROUND(0,s,t);
}
#endif /* ?FULL_UNROLL */
#undef ROUND
/*
* apply last round and
* map cipher state to byte array block:
*/
s0 = TD41(t0) ^ TD42(t3) ^ TD43(t2) ^ TD44(t1) ^ rk[0];
PUTU32(pt , s0);
s1 = TD41(t1) ^ TD42(t0) ^ TD43(t3) ^ TD44(t2) ^ rk[1];
PUTU32(pt + 4, s1);
s2 = TD41(t2) ^ TD42(t1) ^ TD43(t0) ^ TD44(t3) ^ rk[2];
PUTU32(pt + 8, s2);
s3 = TD41(t3) ^ TD42(t2) ^ TD43(t1) ^ TD44(t0) ^ rk[3];
PUTU32(pt + 12, s3);
}
void aes_decrypt(void *ctx, const u8 *crypt, u8 *plain)
{
rijndaelDecrypt(ctx, crypt, plain);
}
void aes_decrypt_deinit(void *ctx)
{
os_memset(ctx, 0, AES_PRIV_SIZE);
os_free(ctx);
}
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