aes-internal-dec.c revision 9bce59c7fef20e34a05f04d1e33a4076083dca0c 
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 */
28static 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
59void * 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
75static 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) \
93d##0 = TD0(s##0) ^ TD1(s##3) ^ TD2(s##2) ^ TD3(s##1) ^ rk[4 * i]; \
94d##1 = TD0(s##1) ^ TD1(s##0) ^ TD2(s##3) ^ TD3(s##2) ^ rk[4 * i + 1]; \
95d##2 = TD0(s##2) ^ TD1(s##1) ^ TD2(s##0) ^ TD3(s##3) ^ rk[4 * i + 2]; \
96d##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
150void 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
157void aes_decrypt_deinit(void *ctx)
158{
159	os_memset(ctx, 0, AES_PRIV_SIZE);
160	os_free(ctx);
161}
162