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@w1.fi>
13 *
14 * This program is free software; you can redistribute it and/or modify
15 * it under the terms of the GNU General Public License version 2 as
16 * published by the Free Software Foundation.
17 *
18 * Alternatively, this software may be distributed under the terms of BSD
19 * license.
20 *
21 * See README and COPYING for more details.
22 */
23
24#include "includes.h"
25
26#include "common.h"
27#include "crypto.h"
28#include "aes_i.h"
29
30/**
31 * Expand the cipher key into the decryption key schedule.
32 *
33 * @return	the number of rounds for the given cipher key size.
34 */
35void rijndaelKeySetupDec(u32 rk[/*44*/], const u8 cipherKey[])
36{
37	int Nr = 10, i, j;
38	u32 temp;
39
40	/* expand the cipher key: */
41	rijndaelKeySetupEnc(rk, cipherKey);
42	/* invert the order of the round keys: */
43	for (i = 0, j = 4*Nr; i < j; i += 4, j -= 4) {
44		temp = rk[i    ]; rk[i    ] = rk[j    ]; rk[j    ] = temp;
45		temp = rk[i + 1]; rk[i + 1] = rk[j + 1]; rk[j + 1] = temp;
46		temp = rk[i + 2]; rk[i + 2] = rk[j + 2]; rk[j + 2] = temp;
47		temp = rk[i + 3]; rk[i + 3] = rk[j + 3]; rk[j + 3] = temp;
48	}
49	/* apply the inverse MixColumn transform to all round keys but the
50	 * first and the last: */
51	for (i = 1; i < Nr; i++) {
52		rk += 4;
53		for (j = 0; j < 4; j++) {
54			rk[j] = TD0_(TE4((rk[j] >> 24)       )) ^
55				TD1_(TE4((rk[j] >> 16) & 0xff)) ^
56				TD2_(TE4((rk[j] >>  8) & 0xff)) ^
57				TD3_(TE4((rk[j]      ) & 0xff));
58		}
59	}
60}
61
62void * aes_decrypt_init(const u8 *key, size_t len)
63{
64	u32 *rk;
65	if (len != 16)
66		return NULL;
67	rk = os_malloc(AES_PRIV_SIZE);
68	if (rk == NULL)
69		return NULL;
70	rijndaelKeySetupDec(rk, key);
71	return rk;
72}
73
74static void rijndaelDecrypt(const u32 rk[/*44*/], const u8 ct[16], u8 pt[16])
75{
76	u32 s0, s1, s2, s3, t0, t1, t2, t3;
77	const int Nr = 10;
78#ifndef FULL_UNROLL
79	int r;
80#endif /* ?FULL_UNROLL */
81
82	/*
83	 * map byte array block to cipher state
84	 * and add initial round key:
85	 */
86	s0 = GETU32(ct     ) ^ rk[0];
87	s1 = GETU32(ct +  4) ^ rk[1];
88	s2 = GETU32(ct +  8) ^ rk[2];
89	s3 = GETU32(ct + 12) ^ rk[3];
90
91#define ROUND(i,d,s) \
92d##0 = TD0(s##0) ^ TD1(s##3) ^ TD2(s##2) ^ TD3(s##1) ^ rk[4 * i]; \
93d##1 = TD0(s##1) ^ TD1(s##0) ^ TD2(s##3) ^ TD3(s##2) ^ rk[4 * i + 1]; \
94d##2 = TD0(s##2) ^ TD1(s##1) ^ TD2(s##0) ^ TD3(s##3) ^ rk[4 * i + 2]; \
95d##3 = TD0(s##3) ^ TD1(s##2) ^ TD2(s##1) ^ TD3(s##0) ^ rk[4 * i + 3]
96
97#ifdef FULL_UNROLL
98
99	ROUND(1,t,s);
100	ROUND(2,s,t);
101	ROUND(3,t,s);
102	ROUND(4,s,t);
103	ROUND(5,t,s);
104	ROUND(6,s,t);
105	ROUND(7,t,s);
106	ROUND(8,s,t);
107	ROUND(9,t,s);
108
109	rk += Nr << 2;
110
111#else  /* !FULL_UNROLL */
112
113	/* Nr - 1 full rounds: */
114	r = Nr >> 1;
115	for (;;) {
116		ROUND(1,t,s);
117		rk += 8;
118		if (--r == 0)
119			break;
120		ROUND(0,s,t);
121	}
122
123#endif /* ?FULL_UNROLL */
124
125#undef ROUND
126
127	/*
128	 * apply last round and
129	 * map cipher state to byte array block:
130	 */
131	s0 = TD41(t0) ^ TD42(t3) ^ TD43(t2) ^ TD44(t1) ^ rk[0];
132	PUTU32(pt     , s0);
133	s1 = TD41(t1) ^ TD42(t0) ^ TD43(t3) ^ TD44(t2) ^ rk[1];
134	PUTU32(pt +  4, s1);
135	s2 = TD41(t2) ^ TD42(t1) ^ TD43(t0) ^ TD44(t3) ^ rk[2];
136	PUTU32(pt +  8, s2);
137	s3 = TD41(t3) ^ TD42(t2) ^ TD43(t1) ^ TD44(t0) ^ rk[3];
138	PUTU32(pt + 12, s3);
139}
140
141void aes_decrypt(void *ctx, const u8 *crypt, u8 *plain)
142{
143	rijndaelDecrypt(ctx, crypt, plain);
144}
145
146
147void aes_decrypt_deinit(void *ctx)
148{
149	os_memset(ctx, 0, AES_PRIV_SIZE);
150	os_free(ctx);
151}
152