Libav
|
00001 /* 00002 * ASF decryption 00003 * Copyright (c) 2007 Reimar Doeffinger 00004 * This is a rewrite of code contained in freeme/freeme2 00005 * 00006 * This file is part of FFmpeg. 00007 * 00008 * FFmpeg is free software; you can redistribute it and/or 00009 * modify it under the terms of the GNU Lesser General Public 00010 * License as published by the Free Software Foundation; either 00011 * version 2.1 of the License, or (at your option) any later version. 00012 * 00013 * FFmpeg is distributed in the hope that it will be useful, 00014 * but WITHOUT ANY WARRANTY; without even the implied warranty of 00015 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 00016 * Lesser General Public License for more details. 00017 * 00018 * You should have received a copy of the GNU Lesser General Public 00019 * License along with FFmpeg; if not, write to the Free Software 00020 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA 00021 */ 00022 00023 #include "libavutil/common.h" 00024 #include "libavutil/intreadwrite.h" 00025 #include "libavutil/bswap.h" 00026 #include "libavutil/des.h" 00027 #include "libavutil/rc4.h" 00028 #include "asfcrypt.h" 00029 00035 static uint32_t inverse(uint32_t v) { 00036 // v ^ 3 gives the inverse (mod 16), could also be implemented 00037 // as table etc. (only lowest 4 bits matter!) 00038 uint32_t inverse = v * v * v; 00039 // uses a fixpoint-iteration that doubles the number 00040 // of correct lowest bits each time 00041 inverse *= 2 - v * inverse; 00042 inverse *= 2 - v * inverse; 00043 inverse *= 2 - v * inverse; 00044 return inverse; 00045 } 00046 00053 static void multiswap_init(const uint8_t keybuf[48], uint32_t keys[12]) { 00054 int i; 00055 for (i = 0; i < 12; i++) 00056 keys[i] = AV_RL32(keybuf + (i << 2)) | 1; 00057 } 00058 00064 static void multiswap_invert_keys(uint32_t keys[12]) { 00065 int i; 00066 for (i = 0; i < 5; i++) 00067 keys[i] = inverse(keys[i]); 00068 for (i = 6; i < 11; i++) 00069 keys[i] = inverse(keys[i]); 00070 } 00071 00072 static uint32_t multiswap_step(const uint32_t keys[12], uint32_t v) { 00073 int i; 00074 v *= keys[0]; 00075 for (i = 1; i < 5; i++) { 00076 v = (v >> 16) | (v << 16); 00077 v *= keys[i]; 00078 } 00079 v += keys[5]; 00080 return v; 00081 } 00082 00083 static uint32_t multiswap_inv_step(const uint32_t keys[12], uint32_t v) { 00084 int i; 00085 v -= keys[5]; 00086 for (i = 4; i > 0; i--) { 00087 v *= keys[i]; 00088 v = (v >> 16) | (v << 16); 00089 } 00090 v *= keys[0]; 00091 return v; 00092 } 00093 00102 static uint64_t multiswap_enc(const uint32_t keys[12], uint64_t key, uint64_t data) { 00103 uint32_t a = data; 00104 uint32_t b = data >> 32; 00105 uint32_t c; 00106 uint32_t tmp; 00107 a += key; 00108 tmp = multiswap_step(keys , a); 00109 b += tmp; 00110 c = (key >> 32) + tmp; 00111 tmp = multiswap_step(keys + 6, b); 00112 c += tmp; 00113 return ((uint64_t)c << 32) | tmp; 00114 } 00115 00124 static uint64_t multiswap_dec(const uint32_t keys[12], uint64_t key, uint64_t data) { 00125 uint32_t a; 00126 uint32_t b; 00127 uint32_t c = data >> 32; 00128 uint32_t tmp = data; 00129 c -= tmp; 00130 b = multiswap_inv_step(keys + 6, tmp); 00131 tmp = c - (key >> 32); 00132 b -= tmp; 00133 a = multiswap_inv_step(keys , tmp); 00134 a -= key; 00135 return ((uint64_t)b << 32) | a; 00136 } 00137 00138 void ff_asfcrypt_dec(const uint8_t key[20], uint8_t *data, int len) { 00139 struct AVDES des; 00140 struct AVRC4 rc4; 00141 int num_qwords = len >> 3; 00142 uint64_t *qwords = (uint64_t *)data; 00143 uint64_t rc4buff[8]; 00144 uint64_t packetkey; 00145 uint32_t ms_keys[12]; 00146 uint64_t ms_state; 00147 int i; 00148 if (len < 16) { 00149 for (i = 0; i < len; i++) 00150 data[i] ^= key[i]; 00151 return; 00152 } 00153 00154 memset(rc4buff, 0, sizeof(rc4buff)); 00155 av_rc4_init(&rc4, key, 12 * 8, 1); 00156 av_rc4_crypt(&rc4, (uint8_t *)rc4buff, NULL, sizeof(rc4buff), NULL, 1); 00157 multiswap_init((uint8_t *)rc4buff, ms_keys); 00158 00159 packetkey = qwords[num_qwords - 1]; 00160 packetkey ^= rc4buff[7]; 00161 av_des_init(&des, key + 12, 64, 1); 00162 av_des_crypt(&des, (uint8_t *)&packetkey, (uint8_t *)&packetkey, 1, NULL, 1); 00163 packetkey ^= rc4buff[6]; 00164 00165 av_rc4_init(&rc4, (uint8_t *)&packetkey, 64, 1); 00166 av_rc4_crypt(&rc4, data, data, len, NULL, 1); 00167 00168 ms_state = 0; 00169 for (i = 0; i < num_qwords - 1; i++, qwords++) 00170 ms_state = multiswap_enc(ms_keys, ms_state, AV_RL64(qwords)); 00171 multiswap_invert_keys(ms_keys); 00172 packetkey = (packetkey << 32) | (packetkey >> 32); 00173 packetkey = le2me_64(packetkey); 00174 packetkey = multiswap_dec(ms_keys, ms_state, packetkey); 00175 AV_WL64(qwords, packetkey); 00176 }