blob: 09e9af6f2c7f0844eb20e517610d4163bda86828 [file] [log] [blame]
 /* * 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 "libavutil/common.h" #include "libavutil/intreadwrite.h" #include "libavutil/bswap.h" #include "libavutil/des.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, uint32_t keys) { 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) { 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, uint32_t v) { int i; v *= keys; for (i = 1; i < 5; i++) { v = (v >> 16) | (v << 16); v *= keys[i]; } v += keys; return v; } static uint32_t multiswap_inv_step(const uint32_t keys, uint32_t v) { int i; v -= keys; for (i = 4; i > 0; i--) { v *= keys[i]; v = (v >> 16) | (v << 16); } v *= keys; 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, 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, 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, uint8_t *data, int len) { struct AVDES des; struct AVRC4 rc4; int num_qwords = len >> 3; uint64_t *qwords = (uint64_t *)data; uint64_t rc4buff; uint64_t packetkey; uint32_t ms_keys; uint64_t ms_state; int i; if (len < 16) { for (i = 0; i < len; i++) data[i] ^= key[i]; return; } memset(rc4buff, 0, sizeof(rc4buff)); 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 = qwords[num_qwords - 1]; packetkey ^= rc4buff; av_des_init(&des, key + 12, 64, 1); av_des_crypt(&des, (uint8_t *)&packetkey, (uint8_t *)&packetkey, 1, NULL, 1); packetkey ^= rc4buff; 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++) ms_state = multiswap_enc(ms_keys, ms_state, AV_RL64(qwords)); multiswap_invert_keys(ms_keys); packetkey = (packetkey << 32) | (packetkey >> 32); packetkey = le2me_64(packetkey); packetkey = multiswap_dec(ms_keys, ms_state, packetkey); AV_WL64(qwords, packetkey); }