libavformat/asfcrypt.c

   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 <stddef.h>
  24 #include "libavutil/bswap.h"
  25 #include "libavutil/des.h"
  26 #include "libavutil/intreadwrite.h"
  27 #include "libavutil/mem.h"
  28 #include "libavutil/rc4.h"
  29 #include "asfcrypt.h"
  30
  31 /**
  32  * @brief find multiplicative inverse modulo 2 ^ 32
  33  * @param v number to invert, must be odd!
  34  * @return number so that result * v = 1 (mod 2^32)
  35  */
  36 static uint32_t inverse(uint32_t v)
  37 {
  38     // v ^ 3 gives the inverse (mod 16), could also be implemented
  39     // as table etc. (only lowest 4 bits matter!)
  40     uint32_t inverse = v * v * v;
  41     // uses a fixpoint-iteration that doubles the number
  42     // of correct lowest bits each time
  43     inverse *= 2 - v * inverse;
  44     inverse *= 2 - v * inverse;
  45     inverse *= 2 - v * inverse;
  46     return inverse;
  47 }
  48
  49 /**
  50  * @brief read keys from keybuf into keys
  51  * @param keybuf buffer containing the keys
  52  * @param keys output key array containing the keys for encryption in
  53  *             native endianness
  54  */
  55 static void multiswap_init(const uint8_t keybuf[48], uint32_t keys[12])
  56 {
  57     int i;
  58     for (i = 0; i < 12; i++)
  59         keys[i] = AV_RL32(keybuf + (i << 2)) | 1;
  60 }
  61
  62 /**
  63  * @brief invert the keys so that encryption become decryption keys and
  64  *        the other way round.
  65  * @param keys key array of ints to invert
  66  */
  67 static void multiswap_invert_keys(uint32_t keys[12])
  68 {
  69     int i;
  70     for (i = 0; i < 5; i++)
  71         keys[i] = inverse(keys[i]);
  72     for (i = 6; i < 11; i++)
  73         keys[i] = inverse(keys[i]);
  74 }
  75
  76 static uint32_t multiswap_step(const uint32_t keys[6], uint32_t v)
  77 {
  78     int i;
  79     v *= keys[0];
  80     for (i = 1; i < 5; i++) {
  81         v  = (v >> 16) | (v << 16);
  82         v *= keys[i];
  83     }
  84     v += keys[5];
  85     return v;
  86 }
  87
  88 static uint32_t multiswap_inv_step(const uint32_t keys[6], uint32_t v)
  89 {
  90     int i;
  91     v -= keys[5];
  92     for (i = 4; i > 0; i--) {
  93         v *= keys[i];
  94         v  = (v >> 16) | (v << 16);
  95     }
  96     v *= keys[0];
  97     return v;
  98 }
  99
 100 /**
 101  * @brief "MultiSwap" encryption
 102  * @param keys 32 bit numbers in machine endianness,
 103  *             0-4 and 6-10 must be inverted from decryption
 104  * @param key another key, this one must be the same for the decryption
 105  * @param data data to encrypt
 106  * @return encrypted data
 107  */
 108 static uint64_t multiswap_enc(const uint32_t keys[12],
 109                               uint64_t key, uint64_t data)
 110 {
 111     uint32_t a = data;
 112     uint32_t b = data >> 32;
 113     uint32_t c;
 114     uint32_t tmp;
 115     a  += key;
 116     tmp = multiswap_step(keys, a);
 117     b  += tmp;
 118     c   = (key >> 32) + tmp;
 119     tmp = multiswap_step(keys + 6, b);
 120     c  += tmp;
 121     return ((uint64_t)c << 32) | tmp;
 122 }
 123
 124 /**
 125  * @brief "MultiSwap" decryption
 126  * @param keys 32 bit numbers in machine endianness,
 127  *             0-4 and 6-10 must be inverted from encryption
 128  * @param key another key, this one must be the same as for the encryption
 129  * @param data data to decrypt
 130  * @return decrypted data
 131  */
 132 static uint64_t multiswap_dec(const uint32_t keys[12],
 133                               uint64_t key, uint64_t data)
 134 {
 135     uint32_t a;
 136     uint32_t b;
 137     uint32_t c   = data >> 32;
 138     uint32_t tmp = data;
 139     c  -= tmp;
 140     b   = multiswap_inv_step(keys + 6, tmp);
 141     tmp = c - (key >> 32);
 142     b  -= tmp;
 143     a   = multiswap_inv_step(keys, tmp);
 144     a  -= key;
 145     return ((uint64_t)b << 32) | a;
 146 }
 147
 148 void ff_asfcrypt_dec(const uint8_t key[20], uint8_t *data, int len)
 149 {
 150     struct AVDES *des;
 151     struct AVRC4 *rc4;
 152     int num_qwords      = len >> 3;
 153     uint8_t *qwords     = data;
 154     uint64_t rc4buff[8] = { 0 };
 155     uint64_t packetkey;
 156     uint32_t ms_keys[12];
 157     uint64_t ms_state;
 158     int i;
 159     if (len < 16) {
 160         for (i = 0; i < len; i++)
 161             data[i] ^= key[i];
 162         return;
 163     }
 164     des = av_des_alloc();
 165     rc4 = av_rc4_alloc();
 166     if (!des || !rc4) {
 167         av_freep(&des);
 168         av_freep(&rc4);
 169         return;
 170     }
 171
 172     av_rc4_init(rc4, key, 12 * 8, 1);
 173     av_rc4_crypt(rc4, (uint8_t *)rc4buff, NULL, sizeof(rc4buff), NULL, 1);
 174     multiswap_init((uint8_t *)rc4buff, ms_keys);
 175
 176     packetkey  = AV_RN64(&qwords[num_qwords * 8 - 8]);
 177     packetkey ^= rc4buff[7];
 178     av_des_init(des, key + 12, 64, 1);
 179     av_des_crypt(des, (uint8_t *)&packetkey, (uint8_t *)&packetkey, 1, NULL, 1);
 180     packetkey ^= rc4buff[6];
 181
 182     av_rc4_init(rc4, (uint8_t *)&packetkey, 64, 1);
 183     av_rc4_crypt(rc4, data, data, len, NULL, 1);
 184
 185     ms_state = 0;
 186     for (i = 0; i < num_qwords - 1; i++, qwords += 8)
 187         ms_state = multiswap_enc(ms_keys, ms_state, AV_RL64(qwords));
 188     multiswap_invert_keys(ms_keys);
 189     packetkey = (packetkey << 32) | (packetkey >> 32);
 190     packetkey = av_le2ne64(packetkey);
 191     packetkey = multiswap_dec(ms_keys, ms_state, packetkey);
 192     AV_WL64(qwords, packetkey);
 193
 194     av_free(rc4);
 195     av_free(des);
 196 }