asfcrypt.c 5.23 KB
Newer Older
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
/*
 * 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
 */
22 23 24 25 26 27

#include "libavutil/common.h"
#include "libavutil/intreadwrite.h"
#include "libavutil/bswap.h"
#include "libavutil/des.h"
#include "libavutil/rc4.h"
28 29 30
#include "asfcrypt.h"

/**
31 32 33
 * @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)
34 35 36 37 38 39 40 41 42 43 44 45 46 47
 */
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;
}

/**
48 49 50
 * @brief read keys from keybuf into keys
 * @param keybuf buffer containing the keys
 * @param keys output key array containing the keys for encryption in
51 52 53 54 55 56 57 58 59
 *             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;
}

/**
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 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94
 */
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[12], 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[12], 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;
}

/**
95 96
 * @brief "MultiSwap" encryption
 * @param keys 32 bit numbers in machine endianness,
97
 *             0-4 and 6-10 must be inverted from decryption
98 99 100
 * @param key another key, this one must be the same for the decryption
 * @param data data to encrypt
 * @return encrypted data
101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116
 */
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;
}

/**
117 118
 * @brief "MultiSwap" decryption
 * @param keys 32 bit numbers in machine endianness,
119
 *             0-4 and 6-10 must be inverted from encryption
120 121 122
 * @param key another key, this one must be the same as for the encryption
 * @param data data to decrypt
 * @return decrypted data
123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138
 */
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) {
139 140
    struct AVDES des;
    struct AVRC4 rc4;
141
    int num_qwords = len >> 3;
142
    uint8_t *qwords = data;
143
    uint64_t rc4buff[8] = { 0 };
144 145 146 147 148 149 150 151 152 153
    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;
    }

154 155
    av_rc4_init(&rc4, key, 12 * 8, 1);
    av_rc4_crypt(&rc4, (uint8_t *)rc4buff, NULL, sizeof(rc4buff), NULL, 1);
156 157
    multiswap_init((uint8_t *)rc4buff, ms_keys);

158
    packetkey = AV_RN64(&qwords[num_qwords*8 - 8]);
159
    packetkey ^= rc4buff[7];
160 161
    av_des_init(&des, key + 12, 64, 1);
    av_des_crypt(&des, (uint8_t *)&packetkey, (uint8_t *)&packetkey, 1, NULL, 1);
162 163
    packetkey ^= rc4buff[6];

164 165
    av_rc4_init(&rc4, (uint8_t *)&packetkey, 64, 1);
    av_rc4_crypt(&rc4, data, data, len, NULL, 1);
166 167

    ms_state = 0;
168
    for (i = 0; i < num_qwords - 1; i++, qwords += 8)
169 170 171
        ms_state = multiswap_enc(ms_keys, ms_state, AV_RL64(qwords));
    multiswap_invert_keys(ms_keys);
    packetkey = (packetkey << 32) | (packetkey >> 32);
172
    packetkey = av_le2ne64(packetkey);
173 174 175
    packetkey = multiswap_dec(ms_keys, ms_state, packetkey);
    AV_WL64(qwords, packetkey);
}