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 "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 30/** 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) 34 */ 35static 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 47/** 48 * \brief read keys from keybuf into keys 49 * \param keybuf buffer containing the keys 50 * \param keys output key array containing the keys for encryption in 51 * native endianness 52 */ 53static 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 59/** 60 * \brief invert the keys so that encryption become decryption keys and 61 * the other way round. 62 * \param keys key array of ints to invert 63 */ 64static 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 72static 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 83static 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 94/** 95 * \brief "MultiSwap" encryption 96 * \param keys 32 bit numbers in machine endianness, 97 * 0-4 and 6-10 must be inverted from decryption 98 * \param key another key, this one must be the same for the decryption 99 * \param data data to encrypt 100 * \return encrypted data 101 */ 102static 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} 115 116/** 117 * \brief "MultiSwap" decryption 118 * \param keys 32 bit numbers in machine endianness, 119 * 0-4 and 6-10 must be inverted from encryption 120 * \param key another key, this one must be the same as for the encryption 121 * \param data data to decrypt 122 * \return decrypted data 123 */ 124static 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 138void 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 uint64_t *qwords = (uint64_t *)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 = qwords[num_qwords - 1]; 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++) 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 = le2me_64(packetkey); 174 packetkey = multiswap_dec(ms_keys, ms_state, packetkey); 175 AV_WL64(qwords, packetkey); 176} 177