asfcrypt.c
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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 Libav.
7  *
8  * Libav 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  * Libav 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 Libav; 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/common.h"
24 #include "libavutil/intreadwrite.h"
25 #include "libavutil/bswap.h"
26 #include "libavutil/des.h"
27 #include "libavutil/rc4.h"
28 #include "asfcrypt.h"
29 
35 static uint32_t inverse(uint32_t v) {
36  // v ^ 3 gives the inverse (mod 16), could also be implemented
37  // as table etc. (only lowest 4 bits matter!)
38  uint32_t inverse = v * v * v;
39  // uses a fixpoint-iteration that doubles the number
40  // of correct lowest bits each time
41  inverse *= 2 - v * inverse;
42  inverse *= 2 - v * inverse;
43  inverse *= 2 - v * inverse;
44  return inverse;
45 }
46 
53 static void multiswap_init(const uint8_t keybuf[48], uint32_t keys[12]) {
54  int i;
55  for (i = 0; i < 12; i++)
56  keys[i] = AV_RL32(keybuf + (i << 2)) | 1;
57 }
58 
64 static void multiswap_invert_keys(uint32_t keys[12]) {
65  int i;
66  for (i = 0; i < 5; i++)
67  keys[i] = inverse(keys[i]);
68  for (i = 6; i < 11; i++)
69  keys[i] = inverse(keys[i]);
70 }
71 
72 static uint32_t multiswap_step(const uint32_t keys[12], uint32_t v) {
73  int i;
74  v *= keys[0];
75  for (i = 1; i < 5; i++) {
76  v = (v >> 16) | (v << 16);
77  v *= keys[i];
78  }
79  v += keys[5];
80  return v;
81 }
82 
83 static uint32_t multiswap_inv_step(const uint32_t keys[12], uint32_t v) {
84  int i;
85  v -= keys[5];
86  for (i = 4; i > 0; i--) {
87  v *= keys[i];
88  v = (v >> 16) | (v << 16);
89  }
90  v *= keys[0];
91  return v;
92 }
93 
102 static uint64_t multiswap_enc(const uint32_t keys[12], uint64_t key, uint64_t data) {
103  uint32_t a = data;
104  uint32_t b = data >> 32;
105  uint32_t c;
106  uint32_t tmp;
107  a += key;
108  tmp = multiswap_step(keys , a);
109  b += tmp;
110  c = (key >> 32) + tmp;
111  tmp = multiswap_step(keys + 6, b);
112  c += tmp;
113  return ((uint64_t)c << 32) | tmp;
114 }
115 
124 static uint64_t multiswap_dec(const uint32_t keys[12], uint64_t key, uint64_t data) {
125  uint32_t a;
126  uint32_t b;
127  uint32_t c = data >> 32;
128  uint32_t tmp = data;
129  c -= tmp;
130  b = multiswap_inv_step(keys + 6, tmp);
131  tmp = c - (key >> 32);
132  b -= tmp;
133  a = multiswap_inv_step(keys , tmp);
134  a -= key;
135  return ((uint64_t)b << 32) | a;
136 }
137 
138 void ff_asfcrypt_dec(const uint8_t key[20], uint8_t *data, int len) {
139  struct AVDES des;
140  struct AVRC4 rc4;
141  int num_qwords = len >> 3;
142  uint8_t *qwords = data;
143  uint64_t rc4buff[8];
144  uint64_t packetkey;
145  uint32_t ms_keys[12];
146  uint64_t ms_state;
147  int i;
148  if (len < 16) {
149  for (i = 0; i < len; i++)
150  data[i] ^= key[i];
151  return;
152  }
153 
154  memset(rc4buff, 0, sizeof(rc4buff));
155  av_rc4_init(&rc4, key, 12 * 8, 1);
156  av_rc4_crypt(&rc4, (uint8_t *)rc4buff, NULL, sizeof(rc4buff), NULL, 1);
157  multiswap_init((uint8_t *)rc4buff, ms_keys);
158 
159  packetkey = AV_RN64(&qwords[num_qwords*8 - 8]);
160  packetkey ^= rc4buff[7];
161  av_des_init(&des, key + 12, 64, 1);
162  av_des_crypt(&des, (uint8_t *)&packetkey, (uint8_t *)&packetkey, 1, NULL, 1);
163  packetkey ^= rc4buff[6];
164 
165  av_rc4_init(&rc4, (uint8_t *)&packetkey, 64, 1);
166  av_rc4_crypt(&rc4, data, data, len, NULL, 1);
167 
168  ms_state = 0;
169  for (i = 0; i < num_qwords - 1; i++, qwords += 8)
170  ms_state = multiswap_enc(ms_keys, ms_state, AV_RL64(qwords));
171  multiswap_invert_keys(ms_keys);
172  packetkey = (packetkey << 32) | (packetkey >> 32);
173  packetkey = av_le2ne64(packetkey);
174  packetkey = multiswap_dec(ms_keys, ms_state, packetkey);
175  AV_WL64(qwords, packetkey);
176 }