yading@11: /*
yading@11:  * ASF decryption
yading@11:  * Copyright (c) 2007 Reimar Doeffinger
yading@11:  * This is a rewrite of code contained in freeme/freeme2
yading@11:  *
yading@11:  * This file is part of FFmpeg.
yading@11:  *
yading@11:  * FFmpeg is free software; you can redistribute it and/or
yading@11:  * modify it under the terms of the GNU Lesser General Public
yading@11:  * License as published by the Free Software Foundation; either
yading@11:  * version 2.1 of the License, or (at your option) any later version.
yading@11:  *
yading@11:  * FFmpeg is distributed in the hope that it will be useful,
yading@11:  * but WITHOUT ANY WARRANTY; without even the implied warranty of
yading@11:  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
yading@11:  * Lesser General Public License for more details.
yading@11:  *
yading@11:  * You should have received a copy of the GNU Lesser General Public
yading@11:  * License along with FFmpeg; if not, write to the Free Software
yading@11:  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
yading@11:  */
yading@11: 
yading@11: #include "libavutil/bswap.h"
yading@11: #include "libavutil/common.h"
yading@11: #include "libavutil/des.h"
yading@11: #include "libavutil/intreadwrite.h"
yading@11: #include "libavutil/rc4.h"
yading@11: #include "asfcrypt.h"
yading@11: 
yading@11: /**
yading@11:  * @brief find multiplicative inverse modulo 2 ^ 32
yading@11:  * @param v number to invert, must be odd!
yading@11:  * @return number so that result * v = 1 (mod 2^32)
yading@11:  */
yading@11: static uint32_t inverse(uint32_t v)
yading@11: {
yading@11:     // v ^ 3 gives the inverse (mod 16), could also be implemented
yading@11:     // as table etc. (only lowest 4 bits matter!)
yading@11:     uint32_t inverse = v * v * v;
yading@11:     // uses a fixpoint-iteration that doubles the number
yading@11:     // of correct lowest bits each time
yading@11:     inverse *= 2 - v * inverse;
yading@11:     inverse *= 2 - v * inverse;
yading@11:     inverse *= 2 - v * inverse;
yading@11:     return inverse;
yading@11: }
yading@11: 
yading@11: /**
yading@11:  * @brief read keys from keybuf into keys
yading@11:  * @param keybuf buffer containing the keys
yading@11:  * @param keys output key array containing the keys for encryption in
yading@11:  *             native endianness
yading@11:  */
yading@11: static void multiswap_init(const uint8_t keybuf[48], uint32_t keys[12])
yading@11: {
yading@11:     int i;
yading@11:     for (i = 0; i < 12; i++)
yading@11:         keys[i] = AV_RL32(keybuf + (i << 2)) | 1;
yading@11: }
yading@11: 
yading@11: /**
yading@11:  * @brief invert the keys so that encryption become decryption keys and
yading@11:  *        the other way round.
yading@11:  * @param keys key array of ints to invert
yading@11:  */
yading@11: static void multiswap_invert_keys(uint32_t keys[12])
yading@11: {
yading@11:     int i;
yading@11:     for (i = 0; i < 5; i++)
yading@11:         keys[i] = inverse(keys[i]);
yading@11:     for (i = 6; i < 11; i++)
yading@11:         keys[i] = inverse(keys[i]);
yading@11: }
yading@11: 
yading@11: static uint32_t multiswap_step(const uint32_t keys[12], uint32_t v)
yading@11: {
yading@11:     int i;
yading@11:     v *= keys[0];
yading@11:     for (i = 1; i < 5; i++) {
yading@11:         v  = (v >> 16) | (v << 16);
yading@11:         v *= keys[i];
yading@11:     }
yading@11:     v += keys[5];
yading@11:     return v;
yading@11: }
yading@11: 
yading@11: static uint32_t multiswap_inv_step(const uint32_t keys[12], uint32_t v)
yading@11: {
yading@11:     int i;
yading@11:     v -= keys[5];
yading@11:     for (i = 4; i > 0; i--) {
yading@11:         v *= keys[i];
yading@11:         v  = (v >> 16) | (v << 16);
yading@11:     }
yading@11:     v *= keys[0];
yading@11:     return v;
yading@11: }
yading@11: 
yading@11: /**
yading@11:  * @brief "MultiSwap" encryption
yading@11:  * @param keys 32 bit numbers in machine endianness,
yading@11:  *             0-4 and 6-10 must be inverted from decryption
yading@11:  * @param key another key, this one must be the same for the decryption
yading@11:  * @param data data to encrypt
yading@11:  * @return encrypted data
yading@11:  */
yading@11: static uint64_t multiswap_enc(const uint32_t keys[12],
yading@11:                               uint64_t key, uint64_t data)
yading@11: {
yading@11:     uint32_t a = data;
yading@11:     uint32_t b = data >> 32;
yading@11:     uint32_t c;
yading@11:     uint32_t tmp;
yading@11:     a  += key;
yading@11:     tmp = multiswap_step(keys, a);
yading@11:     b  += tmp;
yading@11:     c   = (key >> 32) + tmp;
yading@11:     tmp = multiswap_step(keys + 6, b);
yading@11:     c  += tmp;
yading@11:     return ((uint64_t)c << 32) | tmp;
yading@11: }
yading@11: 
yading@11: /**
yading@11:  * @brief "MultiSwap" decryption
yading@11:  * @param keys 32 bit numbers in machine endianness,
yading@11:  *             0-4 and 6-10 must be inverted from encryption
yading@11:  * @param key another key, this one must be the same as for the encryption
yading@11:  * @param data data to decrypt
yading@11:  * @return decrypted data
yading@11:  */
yading@11: static uint64_t multiswap_dec(const uint32_t keys[12],
yading@11:                               uint64_t key, uint64_t data)
yading@11: {
yading@11:     uint32_t a;
yading@11:     uint32_t b;
yading@11:     uint32_t c   = data >> 32;
yading@11:     uint32_t tmp = data;
yading@11:     c  -= tmp;
yading@11:     b   = multiswap_inv_step(keys + 6, tmp);
yading@11:     tmp = c - (key >> 32);
yading@11:     b  -= tmp;
yading@11:     a   = multiswap_inv_step(keys, tmp);
yading@11:     a  -= key;
yading@11:     return ((uint64_t)b << 32) | a;
yading@11: }
yading@11: 
yading@11: void ff_asfcrypt_dec(const uint8_t key[20], uint8_t *data, int len)
yading@11: {
yading@11:     struct AVDES des;
yading@11:     struct AVRC4 rc4;
yading@11:     int num_qwords      = len >> 3;
yading@11:     uint8_t *qwords     = data;
yading@11:     uint64_t rc4buff[8] = { 0 };
yading@11:     uint64_t packetkey;
yading@11:     uint32_t ms_keys[12];
yading@11:     uint64_t ms_state;
yading@11:     int i;
yading@11:     if (len < 16) {
yading@11:         for (i = 0; i < len; i++)
yading@11:             data[i] ^= key[i];
yading@11:         return;
yading@11:     }
yading@11: 
yading@11:     av_rc4_init(&rc4, key, 12 * 8, 1);
yading@11:     av_rc4_crypt(&rc4, (uint8_t *)rc4buff, NULL, sizeof(rc4buff), NULL, 1);
yading@11:     multiswap_init((uint8_t *)rc4buff, ms_keys);
yading@11: 
yading@11:     packetkey  = AV_RN64(&qwords[num_qwords * 8 - 8]);
yading@11:     packetkey ^= rc4buff[7];
yading@11:     av_des_init(&des, key + 12, 64, 1);
yading@11:     av_des_crypt(&des, (uint8_t *)&packetkey, (uint8_t *)&packetkey, 1, NULL, 1);
yading@11:     packetkey ^= rc4buff[6];
yading@11: 
yading@11:     av_rc4_init(&rc4, (uint8_t *)&packetkey, 64, 1);
yading@11:     av_rc4_crypt(&rc4, data, data, len, NULL, 1);
yading@11: 
yading@11:     ms_state = 0;
yading@11:     for (i = 0; i < num_qwords - 1; i++, qwords += 8)
yading@11:         ms_state = multiswap_enc(ms_keys, ms_state, AV_RL64(qwords));
yading@11:     multiswap_invert_keys(ms_keys);
yading@11:     packetkey = (packetkey << 32) | (packetkey >> 32);
yading@11:     packetkey = av_le2ne64(packetkey);
yading@11:     packetkey = multiswap_dec(ms_keys, ms_state, packetkey);
yading@11:     AV_WL64(qwords, packetkey);
yading@11: }