/* * ASF decryption * Copyright (c) 2007 Reimar Doeffinger * This is a rewrite of code contained in freeme/freeme2 * * This file is part of FFmpeg. * * FFmpeg is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * FFmpeg is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with FFmpeg; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ #include <stddef.h>#include "libavutil/bswap.h"#include "libavutil/des.h"#include "libavutil/intreadwrite.h"#include "libavutil/mem.h"#include "libavutil/rc4.h"#include "asfcrypt.h" /** * @brief find multiplicative inverse modulo 2 ^ 32 * @param v number to invert, must be odd! * @return number so that result * v = 1 (mod 2^32) */static uint32_t inverse(uint32_t v){    // v ^ 3 gives the inverse (mod 16), could also be implemented    // as table etc. (only lowest 4 bits matter!)    uint32_t inverse = v * v * v;    // uses a fixpoint-iteration that doubles the number    // of correct lowest bits each time    inverse *= 2 - v * inverse;    inverse *= 2 - v * inverse;    inverse *= 2 - v * inverse;    return inverse;} /** * @brief read keys from keybuf into keys * @param keybuf buffer containing the keys * @param keys output key array containing the keys for encryption in *             native endianness */static void multiswap_init(const uint8_t keybuf[48], uint32_t keys[12]){    int i;    for (i = 0; i < 12; i++)        keys[i] = AV_RL32(keybuf + (i << 2)) | 1;} /** * @brief invert the keys so that encryption become decryption keys and *        the other way round. * @param keys key array of ints to invert */static void multiswap_invert_keys(uint32_t keys[12]){    int i;    for (i = 0; i < 5; i++)        keys[i] = inverse(keys[i]);    for (i = 6; i < 11; i++)        keys[i] = inverse(keys[i]);} static uint32_t multiswap_step(const uint32_t keys[6], uint32_t v){    int i;    v *= keys[0];    for (i = 1; i < 5; i++) {        v  = (v >> 16) | (v << 16);        v *= keys[i];    }    v += keys[5];    return v;} static uint32_t multiswap_inv_step(const uint32_t keys[6], uint32_t v){    int i;    v -= keys[5];    for (i = 4; i > 0; i--) {        v *= keys[i];        v  = (v >> 16) | (v << 16);    }    v *= keys[0];    return v;} /** * @brief "MultiSwap" encryption * @param keys 32 bit numbers in machine endianness, *             0-4 and 6-10 must be inverted from decryption * @param key another key, this one must be the same for the decryption * @param data data to encrypt * @return encrypted data */static uint64_t multiswap_enc(const uint32_t keys[12],                              uint64_t key, uint64_t data){    uint32_t a = data;    uint32_t b = data >> 32;    uint32_t c;    uint32_t tmp;    a  += key;    tmp = multiswap_step(keys, a);    b  += tmp;    c   = (key >> 32) + tmp;    tmp = multiswap_step(keys + 6, b);    c  += tmp;    return ((uint64_t)c << 32) | tmp;} /** * @brief "MultiSwap" decryption * @param keys 32 bit numbers in machine endianness, *             0-4 and 6-10 must be inverted from encryption * @param key another key, this one must be the same as for the encryption * @param data data to decrypt * @return decrypted data */static uint64_t multiswap_dec(const uint32_t keys[12],                              uint64_t key, uint64_t data){    uint32_t a;    uint32_t b;    uint32_t c   = data >> 32;    uint32_t tmp = data;    c  -= tmp;    b   = multiswap_inv_step(keys + 6, tmp);    tmp = c - (key >> 32);    b  -= tmp;    a   = multiswap_inv_step(keys, tmp);    a  -= key;    return ((uint64_t)b << 32) | a;} void ff_asfcrypt_dec(const uint8_t key[20], uint8_t *data, int len){    struct AVDES *des;    struct AVRC4 *rc4;    int num_qwords      = len >> 3;    uint8_t *qwords     = data;    uint64_t rc4buff[8] = { 0 };    uint64_t packetkey;    uint32_t ms_keys[12];    uint64_t ms_state;    int i;    if (len < 16) {        for (i = 0; i < len; i++)            data[i] ^= key[i];        return;    }    des = av_des_alloc();    rc4 = av_rc4_alloc();    if (!des || !rc4) {        av_freep(&des);        av_freep(&rc4);        return;    }     av_rc4_init(rc4, key, 12 * 8, 1);    av_rc4_crypt(rc4, (uint8_t *)rc4buff, NULL, sizeof(rc4buff), NULL, 1);    multiswap_init((uint8_t *)rc4buff, ms_keys);     packetkey  = AV_RN64(&qwords[num_qwords * 8 - 8]);    packetkey ^= rc4buff[7];    av_des_init(des, key + 12, 64, 1);    av_des_crypt(des, (uint8_t *)&packetkey, (uint8_t *)&packetkey, 1, NULL, 1);    packetkey ^= rc4buff[6];     av_rc4_init(rc4, (uint8_t *)&packetkey, 64, 1);    av_rc4_crypt(rc4, data, data, len, NULL, 1);     ms_state = 0;    for (i = 0; i < num_qwords - 1; i++, qwords += 8)        ms_state = multiswap_enc(ms_keys, ms_state, AV_RL64(qwords));    multiswap_invert_keys(ms_keys);    packetkey = (packetkey << 32) | (packetkey >> 32);    packetkey = av_le2ne64(packetkey);    packetkey = multiswap_dec(ms_keys, ms_state, packetkey);    AV_WL64(qwords, packetkey);     av_free(rc4);    av_free(des);}