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 "libavutil/bswap.h"
24 #include "libavutil/common.h"
25 #include "libavutil/des.h"
26 #include "libavutil/intreadwrite.h"
27 #include "libavutil/rc4.h"
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)
35 static uint32_t inverse(uint32_t v
)
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
;
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
54 static void multiswap_init(const uint8_t keybuf
[48], uint32_t keys
[12])
57 for (i
= 0; i
< 12; i
++)
58 keys
[i
] = AV_RL32(keybuf
+ (i
<< 2)) | 1;
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
66 static void multiswap_invert_keys(uint32_t keys
[12])
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
]);
75 static uint32_t multiswap_step(const uint32_t keys
[12], uint32_t v
)
79 for (i
= 1; i
< 5; i
++) {
80 v
= (v
>> 16) | (v
<< 16);
87 static uint32_t multiswap_inv_step(const uint32_t keys
[12], uint32_t v
)
91 for (i
= 4; i
> 0; i
--) {
93 v
= (v
>> 16) | (v
<< 16);
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
107 static uint64_t multiswap_enc(const uint32_t keys
[12],
108 uint64_t key
, uint64_t data
)
111 uint32_t b
= data
>> 32;
115 tmp
= multiswap_step(keys
, a
);
117 c
= (key
>> 32) + tmp
;
118 tmp
= multiswap_step(keys
+ 6, b
);
120 return ((uint64_t)c
<< 32) | tmp
;
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
131 static uint64_t multiswap_dec(const uint32_t keys
[12],
132 uint64_t key
, uint64_t data
)
136 uint32_t c
= data
>> 32;
139 b
= multiswap_inv_step(keys
+ 6, tmp
);
140 tmp
= c
- (key
>> 32);
142 a
= multiswap_inv_step(keys
, tmp
);
144 return ((uint64_t)b
<< 32) | a
;
147 void ff_asfcrypt_dec(const uint8_t key
[20], uint8_t *data
, int len
)
151 int num_qwords
= len
>> 3;
152 uint8_t *qwords
= data
;
153 uint64_t rc4buff
[8] = { 0 };
155 uint32_t ms_keys
[12];
159 for (i
= 0; i
< len
; i
++)
164 av_rc4_init(&rc4
, key
, 12 * 8, 1);
165 av_rc4_crypt(&rc4
, (uint8_t *)rc4buff
, NULL
, sizeof(rc4buff
), NULL
, 1);
166 multiswap_init((uint8_t *)rc4buff
, ms_keys
);
168 packetkey
= AV_RN64(&qwords
[num_qwords
* 8 - 8]);
169 packetkey
^= rc4buff
[7];
170 av_des_init(&des
, key
+ 12, 64, 1);
171 av_des_crypt(&des
, (uint8_t *)&packetkey
, (uint8_t *)&packetkey
, 1, NULL
, 1);
172 packetkey
^= rc4buff
[6];
174 av_rc4_init(&rc4
, (uint8_t *)&packetkey
, 64, 1);
175 av_rc4_crypt(&rc4
, data
, data
, len
, NULL
, 1);
178 for (i
= 0; i
< num_qwords
- 1; i
++, qwords
+= 8)
179 ms_state
= multiswap_enc(ms_keys
, ms_state
, AV_RL64(qwords
));
180 multiswap_invert_keys(ms_keys
);
181 packetkey
= (packetkey
<< 32) | (packetkey
>> 32);
182 packetkey
= av_le2ne64(packetkey
);
183 packetkey
= multiswap_dec(ms_keys
, ms_state
, packetkey
);
184 AV_WL64(qwords
, packetkey
);