aes-internal-dec.c revision c5ec7f57ead87efa365800228aa0b09a12d9e6c4 
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 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 */
29static 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
56void * 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
68static 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) \
86d##0 = TD0(s##0) ^ TD1(s##3) ^ TD2(s##2) ^ TD3(s##1) ^ rk[4 * i]; \
87d##1 = TD0(s##1) ^ TD1(s##0) ^ TD2(s##3) ^ TD3(s##2) ^ rk[4 * i + 1]; \
88d##2 = TD0(s##2) ^ TD1(s##1) ^ TD2(s##0) ^ TD3(s##3) ^ rk[4 * i + 2]; \
89d##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
135void aes_decrypt(void *ctx, const u8 *crypt, u8 *plain)
136{
137	rijndaelDecrypt(ctx, crypt, plain);
138}
139
140
141void aes_decrypt_deinit(void *ctx)
142{
143	os_memset(ctx, 0, AES_PRIV_SIZE);
144	os_free(ctx);
145}
146