Statistics
| Branch: | Revision:

ffmpeg / libavformat / asfcrypt.c @ 890d2799

History | View | Annotate | Download (5.08 KB)

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
#include "common.h"
23
#include "intreadwrite.h"
24
#include "bswap.h"
25
#include "des.h"
26
#include "rc4.h"
27
#include "asfcrypt.h"
28

    
29
/**
30
 * \brief find multiplicative inverse modulo 2 ^ 32
31
 * \param v number to invert, must be odd!
32
 * \return number so that result * v = 1 (mod 2^32)
33
 */
34
static uint32_t inverse(uint32_t v) {
35
    // v ^ 3 gives the inverse (mod 16), could also be implemented
36
    // as table etc. (only lowest 4 bits matter!)
37
    uint32_t inverse = v * v * v;
38
    // uses a fixpoint-iteration that doubles the number
39
    // of correct lowest bits each time
40
    inverse *= 2 - v * inverse;
41
    inverse *= 2 - v * inverse;
42
    inverse *= 2 - v * inverse;
43
    return inverse;
44
}
45

    
46
/**
47
 * \brief read keys from keybuf into keys
48
 * \param keybuf buffer containing the keys
49
 * \param keys output key array containing the keys for encryption in
50
 *             native endianness
51
 */
52
static void multiswap_init(const uint8_t keybuf[48], uint32_t keys[12]) {
53
    int i;
54
    for (i = 0; i < 12; i++)
55
        keys[i] = AV_RL32(keybuf + (i << 2)) | 1;
56
}
57

    
58
/**
59
 * \brief invert the keys so that encryption become decryption keys and
60
 *        the other way round.
61
 * \param keys key array of ints to invert
62
 */
63
static void multiswap_invert_keys(uint32_t keys[12]) {
64
    int i;
65
    for (i = 0; i < 5; i++)
66
        keys[i] = inverse(keys[i]);
67
    for (i = 6; i < 11; i++)
68
        keys[i] = inverse(keys[i]);
69
}
70

    
71
static uint32_t multiswap_step(const uint32_t keys[12], uint32_t v) {
72
    int i;
73
    v *= keys[0];
74
    for (i = 1; i < 5; i++) {
75
        v = (v >> 16) | (v << 16);
76
        v *= keys[i];
77
    }
78
    v += keys[5];
79
    return v;
80
}
81

    
82
static uint32_t multiswap_inv_step(const uint32_t keys[12], uint32_t v) {
83
    int i;
84
    v -= keys[5];
85
    for (i = 4; i > 0; i--) {
86
        v *= keys[i];
87
        v = (v >> 16) | (v << 16);
88
    }
89
    v *= keys[0];
90
    return v;
91
}
92

    
93
/**
94
 * \brief "MultiSwap" encryption
95
 * \param keys 32 bit numbers in machine endianness,
96
 *             0-4 and 6-10 must be inverted from decryption
97
 * \param key another key, this one must be the same for the decryption
98
 * \param data data to encrypt
99
 * \return encrypted data
100
 */
101
static uint64_t multiswap_enc(const uint32_t keys[12], uint64_t key, uint64_t data) {
102
    uint32_t a = data;
103
    uint32_t b = data >> 32;
104
    uint32_t c;
105
    uint32_t tmp;
106
    a += key;
107
    tmp = multiswap_step(keys    , a);
108
    b += tmp;
109
    c = (key >> 32) + tmp;
110
    tmp = multiswap_step(keys + 6, b);
111
    c += tmp;
112
    return ((uint64_t)c << 32) | tmp;
113
}
114

    
115
/**
116
 * \brief "MultiSwap" decryption
117
 * \param keys 32 bit numbers in machine endianness,
118
 *             0-4 and 6-10 must be inverted from encryption
119
 * \param key another key, this one must be the same as for the encryption
120
 * \param data data to decrypt
121
 * \return decrypted data
122
 */
123
static uint64_t multiswap_dec(const uint32_t keys[12], uint64_t key, uint64_t data) {
124
    uint32_t a;
125
    uint32_t b;
126
    uint32_t c = data >> 32;
127
    uint32_t tmp = data;
128
    c -= tmp;
129
    b = multiswap_inv_step(keys + 6, tmp);
130
    tmp = c - (key >> 32);
131
    b -= tmp;
132
    a = multiswap_inv_step(keys    , tmp);
133
    a -= key;
134
    return ((uint64_t)b << 32) | a;
135
}
136

    
137
void ff_asfcrypt_dec(const uint8_t key[20], uint8_t *data, int len) {
138
    int num_qwords = len >> 3;
139
    uint64_t *qwords = (uint64_t *)data;
140
    uint64_t rc4buff[8];
141
    uint64_t packetkey;
142
    uint32_t ms_keys[12];
143
    uint64_t ms_state;
144
    int i;
145
    if (len < 16) {
146
        for (i = 0; i < len; i++)
147
            data[i] ^= key[i];
148
        return;
149
    }
150

    
151
    memset(rc4buff, 0, sizeof(rc4buff));
152
    ff_rc4_enc(key, 12, (uint8_t *)rc4buff, sizeof(rc4buff));
153
    multiswap_init((uint8_t *)rc4buff, ms_keys);
154

    
155
    packetkey = qwords[num_qwords - 1];
156
    packetkey ^= rc4buff[7];
157
    packetkey = be2me_64(packetkey);
158
    packetkey = ff_des_encdec(packetkey, AV_RB64(key + 12), 1);
159
    packetkey = be2me_64(packetkey);
160
    packetkey ^= rc4buff[6];
161

    
162
    ff_rc4_enc((uint8_t *)&packetkey, 8, data, len);
163

    
164
    ms_state = 0;
165
    for (i = 0; i < num_qwords - 1; i++, qwords++)
166
        ms_state = multiswap_enc(ms_keys, ms_state, AV_RL64(qwords));
167
    multiswap_invert_keys(ms_keys);
168
    packetkey = (packetkey << 32) | (packetkey >> 32);
169
    packetkey = le2me_64(packetkey);
170
    packetkey = multiswap_dec(ms_keys, ms_state, packetkey);
171
    AV_WL64(qwords, packetkey);
172
}