1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
|
/*
* ASF decryption
* Copyright (c) 2007 Reimar Doeffinger
* This is a rewrite of code contained in freeme/freeme2
*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include <stddef.h>
#include "libavutil/bswap.h"
#include "libavutil/des.h"
#include "libavutil/intreadwrite.h"
#include "libavutil/mem.h"
#include "libavutil/rc4.h"
#include "asfcrypt.h"
/**
* @brief find multiplicative inverse modulo 2 ^ 32
* @param v number to invert, must be odd!
* @return number so that result * v = 1 (mod 2^32)
*/
static uint32_t inverse(uint32_t v)
{
// v ^ 3 gives the inverse (mod 16), could also be implemented
// as table etc. (only lowest 4 bits matter!)
uint32_t inverse = v * v * v;
// uses a fixpoint-iteration that doubles the number
// of correct lowest bits each time
inverse *= 2 - v * inverse;
inverse *= 2 - v * inverse;
inverse *= 2 - v * inverse;
return inverse;
}
/**
* @brief read keys from keybuf into keys
* @param keybuf buffer containing the keys
* @param keys output key array containing the keys for encryption in
* native endianness
*/
static void multiswap_init(const uint8_t keybuf[48], uint32_t keys[12])
{
int i;
for (i = 0; i < 12; i++)
keys[i] = AV_RL32(keybuf + (i << 2)) | 1;
}
/**
* @brief invert the keys so that encryption become decryption keys and
* the other way round.
* @param keys key array of ints to invert
*/
static void multiswap_invert_keys(uint32_t keys[12])
{
int i;
for (i = 0; i < 5; i++)
keys[i] = inverse(keys[i]);
for (i = 6; i < 11; i++)
keys[i] = inverse(keys[i]);
}
static uint32_t multiswap_step(const uint32_t keys[6], uint32_t v)
{
int i;
v *= keys[0];
for (i = 1; i < 5; i++) {
v = (v >> 16) | (v << 16);
v *= keys[i];
}
v += keys[5];
return v;
}
static uint32_t multiswap_inv_step(const uint32_t keys[6], uint32_t v)
{
int i;
v -= keys[5];
for (i = 4; i > 0; i--) {
v *= keys[i];
v = (v >> 16) | (v << 16);
}
v *= keys[0];
return v;
}
/**
* @brief "MultiSwap" encryption
* @param keys 32 bit numbers in machine endianness,
* 0-4 and 6-10 must be inverted from decryption
* @param key another key, this one must be the same for the decryption
* @param data data to encrypt
* @return encrypted data
*/
static uint64_t multiswap_enc(const uint32_t keys[12],
uint64_t key, uint64_t data)
{
uint32_t a = data;
uint32_t b = data >> 32;
uint32_t c;
uint32_t tmp;
a += key;
tmp = multiswap_step(keys, a);
b += tmp;
c = (key >> 32) + tmp;
tmp = multiswap_step(keys + 6, b);
c += tmp;
return ((uint64_t)c << 32) | tmp;
}
/**
* @brief "MultiSwap" decryption
* @param keys 32 bit numbers in machine endianness,
* 0-4 and 6-10 must be inverted from encryption
* @param key another key, this one must be the same as for the encryption
* @param data data to decrypt
* @return decrypted data
*/
static uint64_t multiswap_dec(const uint32_t keys[12],
uint64_t key, uint64_t data)
{
uint32_t a;
uint32_t b;
uint32_t c = data >> 32;
uint32_t tmp = data;
c -= tmp;
b = multiswap_inv_step(keys + 6, tmp);
tmp = c - (key >> 32);
b -= tmp;
a = multiswap_inv_step(keys, tmp);
a -= key;
return ((uint64_t)b << 32) | a;
}
void ff_asfcrypt_dec(const uint8_t key[20], uint8_t *data, int len)
{
struct AVDES *des;
struct AVRC4 *rc4;
int num_qwords = len >> 3;
uint8_t *qwords = data;
uint64_t rc4buff[8] = { 0 };
uint64_t packetkey;
uint32_t ms_keys[12];
uint64_t ms_state;
int i;
if (len < 16) {
for (i = 0; i < len; i++)
data[i] ^= key[i];
return;
}
des = av_des_alloc();
rc4 = av_rc4_alloc();
if (!des || !rc4) {
av_freep(&des);
av_freep(&rc4);
return;
}
av_rc4_init(rc4, key, 12 * 8, 1);
av_rc4_crypt(rc4, (uint8_t *)rc4buff, NULL, sizeof(rc4buff), NULL, 1);
multiswap_init((uint8_t *)rc4buff, ms_keys);
packetkey = AV_RN64(&qwords[num_qwords * 8 - 8]);
packetkey ^= rc4buff[7];
av_des_init(des, key + 12, 64, 1);
av_des_crypt(des, (uint8_t *)&packetkey, (uint8_t *)&packetkey, 1, NULL, 1);
packetkey ^= rc4buff[6];
av_rc4_init(rc4, (uint8_t *)&packetkey, 64, 1);
av_rc4_crypt(rc4, data, data, len, NULL, 1);
ms_state = 0;
for (i = 0; i < num_qwords - 1; i++, qwords += 8)
ms_state = multiswap_enc(ms_keys, ms_state, AV_RL64(qwords));
multiswap_invert_keys(ms_keys);
packetkey = (packetkey << 32) | (packetkey >> 32);
packetkey = av_le2ne64(packetkey);
packetkey = multiswap_dec(ms_keys, ms_state, packetkey);
AV_WL64(qwords, packetkey);
av_free(rc4);
av_free(des);
}
|
