[FFmpeg-devel] [PATCH] asf decryption support
Reimar Döffinger
Reimar.Doeffinger
Fri Oct 19 16:41:28 CEST 2007
Hello,
this is the final part needed to add asf decryption support (except for
a way to set the key from ffmpeg/ffplay - until that is done MPlayer is one
possible way to test).
Testing on different architectures welcome (though I did test it on
bigendian a few weeks ago and it worked - so rewriting the freeme2 code
had some good side effects beyond LGPL *g*).
FreeMe2 now supposedly can print the key in the format needed by e.g.
MPlayer (though I never used it myself, so don't ask me how to use it).
Greetings,
Reimar D?ffinger
-------------- next part --------------
Index: libavformat/Makefile
===================================================================
--- libavformat/Makefile (revision 10809)
+++ libavformat/Makefile (working copy)
@@ -21,7 +21,7 @@
OBJS-$(CONFIG_AMR_MUXER) += amr.o
OBJS-$(CONFIG_APC_DEMUXER) += apc.o
OBJS-$(CONFIG_APE_DEMUXER) += ape.o
-OBJS-$(CONFIG_ASF_DEMUXER) += asf.o riff.o
+OBJS-$(CONFIG_ASF_DEMUXER) += asf.o asfcrypt.o riff.o
OBJS-$(CONFIG_ASF_MUXER) += asf-enc.o riff.o
OBJS-$(CONFIG_ASF_STREAM_MUXER) += asf-enc.o riff.o
OBJS-$(CONFIG_AU_DEMUXER) += au.o raw.o
Index: libavformat/asf.c
===================================================================
--- libavformat/asf.c (revision 10809)
+++ libavformat/asf.c (working copy)
@@ -23,6 +23,7 @@
#include "mpegaudio.h"
#include "asf.h"
#include "common.h"
+#include "asfcrypt.h"
#undef NDEBUG
#include <assert.h>
@@ -823,6 +824,9 @@
get_buffer(pb, asf_st->pkt.data + asf->packet_frag_offset,
asf->packet_frag_size);
+ if (s->key && s->keylen == 20)
+ ff_asfcrypt_dec(s->key, asf_st->pkt.data + asf->packet_frag_offset,
+ asf->packet_frag_size);
asf_st->frag_offset += asf->packet_frag_size;
/* test if whole packet is read */
if (asf_st->frag_offset == asf_st->pkt.size) {
Index: libavformat/asfcrypt.c
===================================================================
--- libavformat/asfcrypt.c (revision 0)
+++ libavformat/asfcrypt.c (revision 0)
@@ -0,0 +1,172 @@
+/*
+ * 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 "common.h"
+#include "intreadwrite.h"
+#include "bswap.h"
+#include "des.h"
+#include "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[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;
+}
+
+/**
+ * \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) {
+ int num_qwords = len >> 3;
+ uint64_t *qwords = (uint64_t *)data;
+ uint64_t rc4buff[8];
+ 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;
+ }
+
+ memset(rc4buff, 0, sizeof(rc4buff));
+ ff_rc4_enc(key, 12, (uint8_t *)rc4buff, sizeof(rc4buff));
+ multiswap_init((uint8_t *)rc4buff, ms_keys);
+
+ packetkey = qwords[num_qwords - 1];
+ packetkey ^= rc4buff[7];
+ packetkey = be2me_64(packetkey);
+ packetkey = ff_des_encdec(packetkey, AV_RB64(key + 12), 1);
+ packetkey = be2me_64(packetkey);
+ packetkey ^= rc4buff[6];
+
+ ff_rc4_enc((uint8_t *)&packetkey, 8, data, len);
+
+ 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);
+}
Index: libavformat/asfcrypt.h
===================================================================
--- libavformat/asfcrypt.h (revision 0)
+++ libavformat/asfcrypt.h (revision 0)
@@ -0,0 +1,27 @@
+/*
+ * ASF decryption
+ * Copyright (c) 2007 Reimar Doeffinger
+ *
+ * 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
+ */
+
+#ifndef FFMPEG_ASFCRYPT_H
+#define FFMPEG_ASFCRYPT_H
+
+void ff_asfcrypt_dec(const uint8_t key[20], uint8_t *data, int len);
+
+#endif
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