FFmpeg coverage

Directory: ../../../ffmpeg/
File: src/libavformat/asfcrypt.c
Date: 2025-11-04 10:33:36
Exec Total Coverage
Lines: 81 84 96.4%
Functions: 8 8 100.0%
Branches: 18 20 90.0%
Line Branch Exec Source
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 <stddef.h>
24 #include "libavutil/bswap.h"
25 #include "libavutil/des.h"
26 #include "libavutil/intreadwrite.h"
27 #include "libavutil/mem.h"
28 #include "libavutil/rc4.h"
29 #include "asfcrypt.h"
30
31 /**
32 * @brief find multiplicative inverse modulo 2 ^ 32
33 * @param v number to invert, must be odd!
34 * @return number so that result * v = 1 (mod 2^32)
35 */
36 5430 static uint32_t inverse(uint32_t v)
37 {
38 // v ^ 3 gives the inverse (mod 16), could also be implemented
39 // as table etc. (only lowest 4 bits matter!)
40 5430 uint32_t inverse = v * v * v;
41 // uses a fixpoint-iteration that doubles the number
42 // of correct lowest bits each time
43 5430 inverse *= 2 - v * inverse;
44 5430 inverse *= 2 - v * inverse;
45 5430 inverse *= 2 - v * inverse;
46 5430 return inverse;
47 }
48
49 /**
50 * @brief read keys from keybuf into keys
51 * @param keybuf buffer containing the keys
52 * @param keys output key array containing the keys for encryption in
53 * native endianness
54 */
55 543 static void multiswap_init(const uint8_t keybuf[48], uint32_t keys[12])
56 {
57 int i;
58
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 7059 for (i = 0; i < 12; i++)
59 6516 keys[i] = AV_RL32(keybuf + (i << 2)) | 1;
60 543 }
61
62 /**
63 * @brief invert the keys so that encryption become decryption keys and
64 * the other way round.
65 * @param keys key array of ints to invert
66 */
67 543 static void multiswap_invert_keys(uint32_t keys[12])
68 {
69 int i;
70
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71 2715 keys[i] = inverse(keys[i]);
72
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73 2715 keys[i] = inverse(keys[i]);
74 543 }
75
76 90370 static uint32_t multiswap_step(const uint32_t keys[6], uint32_t v)
77 {
78 int i;
79 90370 v *= keys[0];
80
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 451850 for (i = 1; i < 5; i++) {
81 361480 v = (v >> 16) | (v << 16);
82 361480 v *= keys[i];
83 }
84 90370 v += keys[5];
85 90370 return v;
86 }
87
88 1086 static uint32_t multiswap_inv_step(const uint32_t keys[6], uint32_t v)
89 {
90 int i;
91 1086 v -= keys[5];
92
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 5430 for (i = 4; i > 0; i--) {
93 4344 v *= keys[i];
94 4344 v = (v >> 16) | (v << 16);
95 }
96 1086 v *= keys[0];
97 1086 return v;
98 }
99
100 /**
101 * @brief "MultiSwap" encryption
102 * @param keys 32 bit numbers in machine endianness,
103 * 0-4 and 6-10 must be inverted from decryption
104 * @param key another key, this one must be the same for the decryption
105 * @param data data to encrypt
106 * @return encrypted data
107 */
108 45185 static uint64_t multiswap_enc(const uint32_t keys[12],
109 uint64_t key, uint64_t data)
110 {
111 45185 uint32_t a = data;
112 45185 uint32_t b = data >> 32;
113 uint32_t c;
114 uint32_t tmp;
115 45185 a += key;
116 45185 tmp = multiswap_step(keys, a);
117 45185 b += tmp;
118 45185 c = (key >> 32) + tmp;
119 45185 tmp = multiswap_step(keys + 6, b);
120 45185 c += tmp;
121 45185 return ((uint64_t)c << 32) | tmp;
122 }
123
124 /**
125 * @brief "MultiSwap" decryption
126 * @param keys 32 bit numbers in machine endianness,
127 * 0-4 and 6-10 must be inverted from encryption
128 * @param key another key, this one must be the same as for the encryption
129 * @param data data to decrypt
130 * @return decrypted data
131 */
132 543 static uint64_t multiswap_dec(const uint32_t keys[12],
133 uint64_t key, uint64_t data)
134 {
135 uint32_t a;
136 uint32_t b;
137 543 uint32_t c = data >> 32;
138 543 uint32_t tmp = data;
139 543 c -= tmp;
140 543 b = multiswap_inv_step(keys + 6, tmp);
141 543 tmp = c - (key >> 32);
142 543 b -= tmp;
143 543 a = multiswap_inv_step(keys, tmp);
144 543 a -= key;
145 543 return ((uint64_t)b << 32) | a;
146 }
147
148 549 void ff_asfcrypt_dec(const uint8_t key[20], uint8_t *data, int len)
149 {
150 struct AVDES *des;
151 struct AVRC4 *rc4;
152 549 int num_qwords = len >> 3;
153 549 uint8_t *qwords = data;
154 549 uint64_t rc4buff[8] = { 0 };
155 uint64_t packetkey;
156 uint32_t ms_keys[12];
157 uint64_t ms_state;
158 int i;
159
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 549 if (len < 16) {
160
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 26 for (i = 0; i < len; i++)
161 20 data[i] ^= key[i];
162 6 return;
163 }
164 543 des = av_des_alloc();
165 543 rc4 = av_rc4_alloc();
166
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 543 if (!des || !rc4) {
167 ✗ av_freep(&des);
168 ✗ av_freep(&rc4);
169 ✗ return;
170 }
171
172 543 av_rc4_init(rc4, key, 12 * 8, 1);
173 543 av_rc4_crypt(rc4, (uint8_t *)rc4buff, NULL, sizeof(rc4buff), NULL, 1);
174 543 multiswap_init((uint8_t *)rc4buff, ms_keys);
175
176 543 packetkey = AV_RN64(&qwords[num_qwords * 8 - 8]);
177 543 packetkey ^= rc4buff[7];
178 543 av_des_init(des, key + 12, 64, 1);
179 543 av_des_crypt(des, (uint8_t *)&packetkey, (uint8_t *)&packetkey, 1, NULL, 1);
180 543 packetkey ^= rc4buff[6];
181
182 543 av_rc4_init(rc4, (uint8_t *)&packetkey, 64, 1);
183 543 av_rc4_crypt(rc4, data, data, len, NULL, 1);
184
185 543 ms_state = 0;
186
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 45728 for (i = 0; i < num_qwords - 1; i++, qwords += 8)
187 45185 ms_state = multiswap_enc(ms_keys, ms_state, AV_RL64(qwords));
188 543 multiswap_invert_keys(ms_keys);
189 543 packetkey = (packetkey << 32) | (packetkey >> 32);
190 543 packetkey = av_le2ne64(packetkey);
191 543 packetkey = multiswap_dec(ms_keys, ms_state, packetkey);
192 543 AV_WL64(qwords, packetkey);
193
194 543 av_free(rc4);
195 543 av_free(des);
196 }
197