3 * Copyright (c) 2007 Reimar Doeffinger
4 * This is a rewrite of code contained in freeme/freeme2
6 * This file is part of FFmpeg.
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.
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.
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
23 #include "intreadwrite.h"
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)
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;
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
52 static void multiswap_init(const uint8_t keybuf[48], uint32_t keys[12]) {
54 for (i = 0; i < 12; i++)
55 keys[i] = AV_RL32(keybuf + (i << 2)) | 1;
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
63 static void multiswap_invert_keys(uint32_t keys[12]) {
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]);
71 static uint32_t multiswap_step(const uint32_t keys[12], uint32_t v) {
74 for (i = 1; i < 5; i++) {
75 v = (v >> 16) | (v << 16);
82 static uint32_t multiswap_inv_step(const uint32_t keys[12], uint32_t v) {
85 for (i = 4; i > 0; i--) {
87 v = (v >> 16) | (v << 16);
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
101 static uint64_t multiswap_enc(const uint32_t keys[12], uint64_t key, uint64_t data) {
103 uint32_t b = data >> 32;
107 tmp = multiswap_step(keys , a);
109 c = (key >> 32) + tmp;
110 tmp = multiswap_step(keys + 6, b);
112 return ((uint64_t)c << 32) | tmp;
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
123 static uint64_t multiswap_dec(const uint32_t keys[12], uint64_t key, uint64_t data) {
126 uint32_t c = data >> 32;
129 b = multiswap_inv_step(keys + 6, tmp);
130 tmp = c - (key >> 32);
132 a = multiswap_inv_step(keys , tmp);
134 return ((uint64_t)b << 32) | a;
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;
142 uint32_t ms_keys[12];
146 for (i = 0; i < len; i++)
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);
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];
162 ff_rc4_enc((uint8_t *)&packetkey, 8, data, len);
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);