blob: 221a8a89bc013737efd8cad0c74e3f97f9dccdc1
1 | /* |
2 | * ASF decryption |
3 | * Copyright (c) 2007 Reimar Doeffinger |
4 | * This is a rewrite of code contained in freeme/freeme2 |
5 | * |
6 | * This file is part of FFmpeg. |
7 | * |
8 | * FFmpeg is free software; you can redistribute it and/or |
9 | * modify it under the terms of the GNU Lesser General Public |
10 | * License as published by the Free Software Foundation; either |
11 | * version 2.1 of the License, or (at your option) any later version. |
12 | * |
13 | * FFmpeg is distributed in the hope that it will be useful, |
14 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
15 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
16 | * Lesser General Public License for more details. |
17 | * |
18 | * You should have received a copy of the GNU Lesser General Public |
19 | * License along with FFmpeg; if not, write to the Free Software |
20 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
21 | */ |
22 | |
23 | #include "libavutil/bswap.h" |
24 | #include "libavutil/common.h" |
25 | #include "libavutil/des.h" |
26 | #include "libavutil/intreadwrite.h" |
27 | #include "libavutil/rc4.h" |
28 | #include "asfcrypt.h" |
29 | |
30 | /** |
31 | * @brief find multiplicative inverse modulo 2 ^ 32 |
32 | * @param v number to invert, must be odd! |
33 | * @return number so that result * v = 1 (mod 2^32) |
34 | */ |
35 | static uint32_t inverse(uint32_t v) |
36 | { |
37 | // v ^ 3 gives the inverse (mod 16), could also be implemented |
38 | // as table etc. (only lowest 4 bits matter!) |
39 | uint32_t inverse = v * v * v; |
40 | // uses a fixpoint-iteration that doubles the number |
41 | // of correct lowest bits each time |
42 | inverse *= 2 - v * inverse; |
43 | inverse *= 2 - v * inverse; |
44 | inverse *= 2 - v * inverse; |
45 | return inverse; |
46 | } |
47 | |
48 | /** |
49 | * @brief read keys from keybuf into keys |
50 | * @param keybuf buffer containing the keys |
51 | * @param keys output key array containing the keys for encryption in |
52 | * native endianness |
53 | */ |
54 | static void multiswap_init(const uint8_t keybuf[48], uint32_t keys[12]) |
55 | { |
56 | int i; |
57 | for (i = 0; i < 12; i++) |
58 | keys[i] = AV_RL32(keybuf + (i << 2)) | 1; |
59 | } |
60 | |
61 | /** |
62 | * @brief invert the keys so that encryption become decryption keys and |
63 | * the other way round. |
64 | * @param keys key array of ints to invert |
65 | */ |
66 | static void multiswap_invert_keys(uint32_t keys[12]) |
67 | { |
68 | int i; |
69 | for (i = 0; i < 5; i++) |
70 | keys[i] = inverse(keys[i]); |
71 | for (i = 6; i < 11; i++) |
72 | keys[i] = inverse(keys[i]); |
73 | } |
74 | |
75 | static uint32_t multiswap_step(const uint32_t keys[12], uint32_t v) |
76 | { |
77 | int i; |
78 | v *= keys[0]; |
79 | for (i = 1; i < 5; i++) { |
80 | v = (v >> 16) | (v << 16); |
81 | v *= keys[i]; |
82 | } |
83 | v += keys[5]; |
84 | return v; |
85 | } |
86 | |
87 | static uint32_t multiswap_inv_step(const uint32_t keys[12], uint32_t v) |
88 | { |
89 | int i; |
90 | v -= keys[5]; |
91 | for (i = 4; i > 0; i--) { |
92 | v *= keys[i]; |
93 | v = (v >> 16) | (v << 16); |
94 | } |
95 | v *= keys[0]; |
96 | return v; |
97 | } |
98 | |
99 | /** |
100 | * @brief "MultiSwap" encryption |
101 | * @param keys 32 bit numbers in machine endianness, |
102 | * 0-4 and 6-10 must be inverted from decryption |
103 | * @param key another key, this one must be the same for the decryption |
104 | * @param data data to encrypt |
105 | * @return encrypted data |
106 | */ |
107 | static uint64_t multiswap_enc(const uint32_t keys[12], |
108 | uint64_t key, uint64_t data) |
109 | { |
110 | uint32_t a = data; |
111 | uint32_t b = data >> 32; |
112 | uint32_t c; |
113 | uint32_t tmp; |
114 | a += key; |
115 | tmp = multiswap_step(keys, a); |
116 | b += tmp; |
117 | c = (key >> 32) + tmp; |
118 | tmp = multiswap_step(keys + 6, b); |
119 | c += tmp; |
120 | return ((uint64_t)c << 32) | tmp; |
121 | } |
122 | |
123 | /** |
124 | * @brief "MultiSwap" decryption |
125 | * @param keys 32 bit numbers in machine endianness, |
126 | * 0-4 and 6-10 must be inverted from encryption |
127 | * @param key another key, this one must be the same as for the encryption |
128 | * @param data data to decrypt |
129 | * @return decrypted data |
130 | */ |
131 | static uint64_t multiswap_dec(const uint32_t keys[12], |
132 | uint64_t key, uint64_t data) |
133 | { |
134 | uint32_t a; |
135 | uint32_t b; |
136 | uint32_t c = data >> 32; |
137 | uint32_t tmp = data; |
138 | c -= tmp; |
139 | b = multiswap_inv_step(keys + 6, tmp); |
140 | tmp = c - (key >> 32); |
141 | b -= tmp; |
142 | a = multiswap_inv_step(keys, tmp); |
143 | a -= key; |
144 | return ((uint64_t)b << 32) | a; |
145 | } |
146 | |
147 | void ff_asfcrypt_dec(const uint8_t key[20], uint8_t *data, int len) |
148 | { |
149 | struct AVDES *des; |
150 | struct AVRC4 *rc4; |
151 | int num_qwords = len >> 3; |
152 | uint8_t *qwords = data; |
153 | uint64_t rc4buff[8] = { 0 }; |
154 | uint64_t packetkey; |
155 | uint32_t ms_keys[12]; |
156 | uint64_t ms_state; |
157 | int i; |
158 | if (len < 16) { |
159 | for (i = 0; i < len; i++) |
160 | data[i] ^= key[i]; |
161 | return; |
162 | } |
163 | des = av_des_alloc(); |
164 | rc4 = av_rc4_alloc(); |
165 | if (!des || !rc4) { |
166 | av_freep(&des); |
167 | av_freep(&rc4); |
168 | return; |
169 | } |
170 | |
171 | av_rc4_init(rc4, key, 12 * 8, 1); |
172 | av_rc4_crypt(rc4, (uint8_t *)rc4buff, NULL, sizeof(rc4buff), NULL, 1); |
173 | multiswap_init((uint8_t *)rc4buff, ms_keys); |
174 | |
175 | packetkey = AV_RN64(&qwords[num_qwords * 8 - 8]); |
176 | packetkey ^= rc4buff[7]; |
177 | av_des_init(des, key + 12, 64, 1); |
178 | av_des_crypt(des, (uint8_t *)&packetkey, (uint8_t *)&packetkey, 1, NULL, 1); |
179 | packetkey ^= rc4buff[6]; |
180 | |
181 | av_rc4_init(rc4, (uint8_t *)&packetkey, 64, 1); |
182 | av_rc4_crypt(rc4, data, data, len, NULL, 1); |
183 | |
184 | ms_state = 0; |
185 | for (i = 0; i < num_qwords - 1; i++, qwords += 8) |
186 | ms_state = multiswap_enc(ms_keys, ms_state, AV_RL64(qwords)); |
187 | multiswap_invert_keys(ms_keys); |
188 | packetkey = (packetkey << 32) | (packetkey >> 32); |
189 | packetkey = av_le2ne64(packetkey); |
190 | packetkey = multiswap_dec(ms_keys, ms_state, packetkey); |
191 | AV_WL64(qwords, packetkey); |
192 | |
193 | av_free(rc4); |
194 | av_free(des); |
195 | } |
196 |