videolan
/
vlc
mirror of https://gitea.goldendeliverer.com/videolan/vlc.git
1
0
Fork 0
Code Issues Projects Releases Wiki Activity
You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
970 Commits
7 Branches
132 Tags
718 MiB
 
 
 
 
 
 
Tree: 9727b87f36
Branches Tags
${ item.name }
Create tag ${ searchTerm }
Create branch ${ searchTerm }
from '9727b87f36'
${ noResults }
vlc/extras/libdvdcss/css.c

816 lines
25 KiB
Raw Blame History

/*****************************************************************************
* css.c: Functions for DVD authentification and unscrambling
*****************************************************************************
* Copyright (C) 1999-2001 VideoLAN
* $Id: css.c,v 1.5 2001/07/11 02:01:03 sam Exp $
*
* Author: Stéphane Borel <stef@via.ecp.fr>
*
* based on:
* - css-auth by Derek Fawcus <derek@spider.com>
* - DVD CSS ioctls example program by Andrew T. Veliath <andrewtv@usa.net>
* - The Divide and conquer attack by Frank A. Stevenson <frank@funcom.com>
* - DeCSSPlus by Ethan Hawke
* - DecVOB
* see http://www.lemuria.org/DeCSS/ by Tom Vogt for more information.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111, USA.
*****************************************************************************/
/*****************************************************************************
* Preamble
*****************************************************************************/
#include "defs.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "config.h"
#include "common.h"
#include "videolan/dvdcss.h"
#include "libdvdcss.h"
#ifdef HAVE_CSS
# include "csstables.h"
#endif /* HAVE_CSS */
#include "ioctl.h"
/*****************************************************************************
* Local prototypes
*****************************************************************************/
#ifdef HAVE_CSS
static int CSSGetASF ( dvdcss_handle dvdcss );
static void CSSCryptKey ( int i_key_type, int i_varient,
u8 const * p_challenge, u8* p_key );
static int CSSCracker ( int i_start, unsigned char * p_crypted,
unsigned char * p_decrypted,
dvd_key_t * p_sector_key, dvd_key_t * p_key );
#endif /* HAVE_CSS */
/*****************************************************************************
* CSSTest : check if the disc is encrypted or not
*****************************************************************************/
int CSSTest( dvdcss_handle dvdcss )
{
int i_ret, i_copyright;
i_ret = ioctl_ReadCopyright( dvdcss->i_fd, 0 /* i_layer */, &i_copyright );
if( i_ret < 0 )
{
/* Since it's the first ioctl we try to issue, we add a notice */
_dvdcss_error( dvdcss, "css error: ioctl_ReadCopyright failed, "
"make sure DVD ioctls were compiled in" );
return i_ret;
}
return i_copyright;
}
/*****************************************************************************
* CSSInit : CSS Structure initialisation and DVD authentication.
*****************************************************************************
* It simulates the mutual authentication between logical unit and host.
* Since we don't need the disc key to find the title key, we just run the
* basic unavoidable commands to authenticate device and disc.
*****************************************************************************/
int CSSInit( dvdcss_handle dvdcss )
{
#ifdef HAVE_CSS
/* structures defined in cdrom.h or dvdio.h */
unsigned char p_buffer[2048 + 4 + 1];
char psz_warning[32];
int i_agid = 0;
int i_ret = -1;
int i;
/* Test authentication success */
switch( CSSGetASF( dvdcss ) )
{
case -1:
return -1;
case 1:
_dvdcss_debug( dvdcss, "already authenticated" );
return 0;
case 0:
_dvdcss_debug( dvdcss, "need to authenticate" );
}
/* Init sequence, request AGID */
for( i = 1; i < 4 ; ++i )
{
sprintf( psz_warning, "requesting AGID %d", i );
_dvdcss_debug( dvdcss, psz_warning );
i_ret = ioctl_ReportAgid( dvdcss->i_fd, &i_agid );
if( i_ret != -1 )
{
/* No error during ioctl: we know the device is authenticated */
break;
}
_dvdcss_error( dvdcss, "ioctl_ReportAgid failed, invalidating" );
i_agid = 0;
ioctl_InvalidateAgid( dvdcss->i_fd, &i_agid );
}
/* Unable to authenticate without AGID */
if( i_ret == -1 )
{
_dvdcss_error( dvdcss, "ioctl_ReportAgid failed, fatal" );
return -1;
}
for( i = 0 ; i < 10; ++i )
{
dvdcss->css.disc.p_challenge[i] = i;
}
/* Get challenge from host */
for( i = 0 ; i < 10 ; ++i )
{
p_buffer[9-i] = dvdcss->css.disc.p_challenge[i];
}
/* Send challenge to LU */
if( ioctl_SendChallenge( dvdcss->i_fd, &i_agid, p_buffer ) < 0 )
{
_dvdcss_error( dvdcss, "ioctl_SendChallenge failed" );
return -1;
}
/* Get key1 from LU */
if( ioctl_ReportKey1( dvdcss->i_fd, &i_agid, p_buffer ) < 0)
{
_dvdcss_error( dvdcss, "ioctl_ReportKey1 failed" );
return -1;
}
/* Send key1 to host */
for( i = 0 ; i < KEY_SIZE ; i++ )
{
dvdcss->css.disc.p_key1[i] = p_buffer[4-i];
}
for( i = 0 ; i < 32 ; ++i )
{
CSSCryptKey( 0, i, dvdcss->css.disc.p_challenge,
dvdcss->css.disc.p_key_check );
if( memcmp( dvdcss->css.disc.p_key_check,
dvdcss->css.disc.p_key1, KEY_SIZE ) == 0 )
{
sprintf( psz_warning, "drive authentic, using variant %d", i );
_dvdcss_debug( dvdcss, psz_warning );
dvdcss->css.disc.i_varient = i;
break;
}
}
if( i == 32 )
{
_dvdcss_error( dvdcss, "drive would not authenticate" );
return -1;
}
/* Get challenge from LU */
if( ioctl_ReportChallenge( dvdcss->i_fd, &i_agid, p_buffer ) < 0 )
{
_dvdcss_error( dvdcss, "ioctl_ReportKeyChallenge failed" );
return -1;
}
/* Send challenge to host */
for( i = 0 ; i < 10 ; ++i )
{
dvdcss->css.disc.p_challenge[i] = p_buffer[9-i];
}
CSSCryptKey( 1, dvdcss->css.disc.i_varient,
dvdcss->css.disc.p_challenge,
dvdcss->css.disc.p_key2 );
/* Get key2 from host */
for( i = 0 ; i < KEY_SIZE ; ++i )
{
p_buffer[4-i] = dvdcss->css.disc.p_key2[i];
}
/* Send key2 to LU */
if( ioctl_SendKey2( dvdcss->i_fd, &i_agid, p_buffer ) < 0 )
{
_dvdcss_error( dvdcss, "ioctl_SendKey2 failed" );
return -1;
}
_dvdcss_debug( dvdcss, "authentication established" );
memcpy( dvdcss->css.disc.p_challenge,
dvdcss->css.disc.p_key1, KEY_SIZE );
memcpy( dvdcss->css.disc.p_challenge+KEY_SIZE,
dvdcss->css.disc.p_key2, KEY_SIZE );
CSSCryptKey( 2, dvdcss->css.disc.i_varient,
dvdcss->css.disc.p_challenge,
dvdcss->css.disc.p_key_check );
_dvdcss_debug( dvdcss, "received session key" );
if( i_agid < 0 )
{
return -1;
}
/* Test authentication success */
switch( CSSGetASF( dvdcss ) )
{
case -1:
return -1;
case 1:
_dvdcss_debug( dvdcss, "already authenticated" );
return 0;
case 0:
_dvdcss_debug( dvdcss, "need to get disc key" );
}
/* Get encrypted disc key */
if( ioctl_ReadKey( dvdcss->i_fd, &i_agid, p_buffer ) < 0 )
{
_dvdcss_error( dvdcss, "ioctl_ReadKey failed" );
return -1;
}
fprintf( stderr, "DISK KEY: %02x %02x %02x %02x %02x\n", p_buffer[0], p_buffer[1], p_buffer[2], p_buffer[3], p_buffer[4] );
/* Unencrypt disc key using bus key */
for( i = 0 ; i < 2048 ; i++ )
{
p_buffer[ i ] ^= dvdcss->css.disc.p_key_check[ 4 - (i % KEY_SIZE) ];
}
memcpy( dvdcss->css.disc.p_key_check, p_buffer, 2048 );
/* Test authentication success */
switch( CSSGetASF( dvdcss ) )
{
case -1:
return -1;
case 1:
_dvdcss_debug( dvdcss, "successfully authenticated" );
return 0;
case 0:
_dvdcss_error( dvdcss, "no way to authenticate" );
return -1;
}
#else /* HAVE_CSS */
_dvdcss_error( dvdcss, "CSS decryption is disabled in this module" );
#endif /* HAVE_CSS */
return -1;
}
/*****************************************************************************
* CSSGetKey : get title key.
*****************************************************************************
* The DVD should have been opened and authenticated before.
*****************************************************************************/
int CSSGetKey( dvdcss_handle dvdcss, int i_pos, dvd_key_t p_titlekey )
{
#ifdef HAVE_CSS
/*
* Title key cracking method from Ethan Hawke,
* with Frank A. Stevenson algorithm.
* Does not use any player key table and ioctls.
*/
u8 p_buf[0x800];
dvd_key_t p_key;
boolean_t b_encrypted;
boolean_t b_stop_scanning;
int i_blocks_read;
int i_best_plen;
int i_best_p;
int i,j;
for( i = 0 ; i < KEY_SIZE ; i++ )
{
p_key[i] = 0;
}
b_encrypted = 0;
b_stop_scanning = 0;
do
{
i_pos = dvdcss_seek( dvdcss, i_pos );
i_blocks_read = dvdcss_read( dvdcss, p_buf, 1, DVDCSS_NOFLAGS );
/* PES_scrambling_control */
if( p_buf[0x14] & 0x30 )
{
b_encrypted = 1;
i_best_plen = 0;
i_best_p = 0;
for( i = 2 ; i < 0x30 ; i++ )
{
for( j = i+1 ;
j < 0x80 && ( p_buf[0x7F - (j%i)] == p_buf[0x7F-j] );
j++ );
{
if( j > i_best_plen )
{
i_best_plen = j;
i_best_p = i;
}
}
}
if( ( i_best_plen > 20 ) && ( i_best_plen / i_best_p >= 2) )
{
i = CSSCracker( 0, &p_buf[0x80],
&p_buf[0x80 - ( i_best_plen / i_best_p) *i_best_p],
(dvd_key_t*)&p_buf[0x54],
&p_key );
b_stop_scanning = ( i >= 0 );
}
}
i_pos += i_blocks_read;
} while( i_blocks_read == 0x1 && !b_stop_scanning );
if( b_stop_scanning )
{
memcpy( p_titlekey, &p_key, sizeof(dvd_key_t) );
_dvdcss_debug( dvdcss, "vts key initialized" );
return 0;
}
if( !b_encrypted )
{
_dvdcss_debug( dvdcss, "file was unscrambled" );
return 0;
}
return -1;
#else /* HAVE_CSS */
_dvdcss_error( dvdcss, "css decryption unavailable" );
return -1;
#endif /* HAVE_CSS */
}
/*****************************************************************************
* CSSDescrambleSector
*****************************************************************************
* sec : sector to descramble
* key : title key for this sector
*****************************************************************************/
int CSSDescrambleSector( dvd_key_t p_key, u8* p_sec )
{
#ifdef HAVE_CSS
unsigned int i_t1, i_t2, i_t3, i_t4, i_t5, i_t6;
u8* p_end = p_sec + 0x800;
/* PES_scrambling_control */
if( p_sec[0x14] & 0x30)
{
i_t1 = ((p_key)[0] ^ p_sec[0x54]) | 0x100;
i_t2 = (p_key)[1] ^ p_sec[0x55];
i_t3 = (((p_key)[2]) | ((p_key)[3] << 8) |
((p_key)[4] << 16)) ^ ((p_sec[0x56]) |
(p_sec[0x57] << 8) | (p_sec[0x58] << 16));
i_t4 = i_t3 & 7;
i_t3 = i_t3 * 2 + 8 - i_t4;
p_sec += 0x80;
i_t5 = 0;
while( p_sec != p_end )
{
i_t4 = p_css_tab2[i_t2] ^ p_css_tab3[i_t1];
i_t2 = i_t1>>1;
i_t1 = ( ( i_t1 & 1 ) << 8 ) ^ i_t4;
i_t4 = p_css_tab5[i_t4];
i_t6 = ((((((( i_t3 >> 3 ) ^ i_t3 ) >> 1 ) ^
i_t3 ) >> 8 ) ^ i_t3 ) >> 5) & 0xff;
i_t3 = (i_t3 << 8 ) | i_t6;
i_t6 = p_css_tab4[i_t6];
i_t5 += i_t6 + i_t4;
*p_sec = p_css_tab1[*p_sec] ^( i_t5 & 0xff );
p_sec++;
i_t5 >>= 8;
}
}
return 0;
#else /* HAVE_CSS */
return 1;
#endif /* HAVE_CSS */
}
#ifdef HAVE_CSS
/* Following functions are local */
/*****************************************************************************
* CSSGetASF : Get Authentification success flag
*****************************************************************************
* Returns :
* -1 on ioctl error,
* 0 if the device needs to be authenticated,
* 1 either.
*****************************************************************************/
static int CSSGetASF( dvdcss_handle dvdcss )
{
int i_agid;
int i_asf = 0;
for( i_agid = 0 ; i_agid < 4 ; i_agid++ )
{
if( ioctl_ReportASF( dvdcss->i_fd, &i_agid, &i_asf ) == 0 )
{
if( i_asf )
{
_dvdcss_debug( dvdcss, "GetASF authenticated" );
}
else
{
_dvdcss_debug( dvdcss, "GetASF not authenticated" );
}
return i_asf;
}
}
/* The ioctl process has failed */
_dvdcss_error( dvdcss, "GetASF fatal error" );
return -1;
}
/*****************************************************************************
* CSSCryptKey : shuffles bits and unencrypt keys.
*****************************************************************************
* Used during authentication and disc key negociation in CSSInit.
* i_key_type : 0->key1, 1->key2, 2->buskey.
* i_varient : between 0 and 31.
*****************************************************************************/
static void CSSCryptKey( int i_key_type, int i_varient,
u8 const * p_challenge, u8* p_key )
{
/* Permutation table for challenge */
u8 pp_perm_challenge[3][10] =
{ { 1, 3, 0, 7, 5, 2, 9, 6, 4, 8 },
{ 6, 1, 9, 3, 8, 5, 7, 4, 0, 2 },
{ 4, 0, 3, 5, 7, 2, 8, 6, 1, 9 } };
/* Permutation table for varient table for key2 and buskey */
u8 pp_perm_varient[2][32] =
{ { 0x0a, 0x08, 0x0e, 0x0c, 0x0b, 0x09, 0x0f, 0x0d,
0x1a, 0x18, 0x1e, 0x1c, 0x1b, 0x19, 0x1f, 0x1d,
0x02, 0x00, 0x06, 0x04, 0x03, 0x01, 0x07, 0x05,
0x12, 0x10, 0x16, 0x14, 0x13, 0x11, 0x17, 0x15 },
{ 0x12, 0x1a, 0x16, 0x1e, 0x02, 0x0a, 0x06, 0x0e,
0x10, 0x18, 0x14, 0x1c, 0x00, 0x08, 0x04, 0x0c,
0x13, 0x1b, 0x17, 0x1f, 0x03, 0x0b, 0x07, 0x0f,
0x11, 0x19, 0x15, 0x1d, 0x01, 0x09, 0x05, 0x0d } };
u8 p_varients[32] =
{ 0xB7, 0x74, 0x85, 0xD0, 0xCC, 0xDB, 0xCA, 0x73,
0x03, 0xFE, 0x31, 0x03, 0x52, 0xE0, 0xB7, 0x42,
0x63, 0x16, 0xF2, 0x2A, 0x79, 0x52, 0xFF, 0x1B,
0x7A, 0x11, 0xCA, 0x1A, 0x9B, 0x40, 0xAD, 0x01 };
/* The "secret" key */
u8 p_secret[5] = { 0x55, 0xD6, 0xC4, 0xC5, 0x28 };
u8 p_bits[30];
u8 p_scratch[10];
u8 p_tmp1[5];
u8 p_tmp2[5];
u8 i_lfsr0_o; /* 1 bit used */
u8 i_lfsr1_o; /* 1 bit used */
u32 i_lfsr0;
u32 i_lfsr1;
u8 i_css_varient;
u8 i_cse;
u8 i_index;
u8 i_combined;
u8 i_carry;
u8 i_val = 0;
int i_term = 0;
int i_bit;
int i;
for (i = 9; i >= 0; --i)
p_scratch[i] = p_challenge[pp_perm_challenge[i_key_type][i]];
i_css_varient = ( i_key_type == 0 ) ? i_varient :
pp_perm_varient[i_key_type-1][i_varient];
/*
* This encryption engine implements one of 32 variations
* one the same theme depending upon the choice in the
* varient parameter (0 - 31).
*
* The algorithm itself manipulates a 40 bit input into
* a 40 bit output.
* The parameter 'input' is 80 bits. It consists of
* the 40 bit input value that is to be encrypted followed
* by a 40 bit seed value for the pseudo random number
* generators.
*/
/* Feed the secret into the input values such that
* we alter the seed to the LFSR's used above, then
* generate the bits to play with.
*/
for( i = 5 ; --i >= 0 ; )
{
p_tmp1[i] = p_scratch[5 + i] ^ p_secret[i] ^ p_crypt_tab2[i];
}
/*
* We use two LFSR's (seeded from some of the input data bytes) to
* generate two streams of pseudo-random bits. These two bit streams
* are then combined by simply adding with carry to generate a final
* sequence of pseudo-random bits which is stored in the buffer that
* 'output' points to the end of - len is the size of this buffer.
*
* The first LFSR is of degree 25, and has a polynomial of:
* x^13 + x^5 + x^4 + x^1 + 1
*
* The second LSFR is of degree 17, and has a (primitive) polynomial of:
* x^15 + x^1 + 1
*
* I don't know if these polynomials are primitive modulo 2, and thus
* represent maximal-period LFSR's.
*
*
* Note that we take the output of each LFSR from the new shifted in
* bit, not the old shifted out bit. Thus for ease of use the LFSR's
* are implemented in bit reversed order.
*
*/
/* In order to ensure that the LFSR works we need to ensure that the
* initial values are non-zero. Thus when we initialise them from
* the seed, we ensure that a bit is set.
*/
i_lfsr0 = ( p_tmp1[0] << 17 ) | ( p_tmp1[1] << 9 ) |
(( p_tmp1[2] & ~7 ) << 1 ) | 8 | ( p_tmp1[2] & 7 );
i_lfsr1 = ( p_tmp1[3] << 9 ) | 0x100 | p_tmp1[4];
i_index = sizeof(p_bits);
i_carry = 0;
do
{
for( i_bit = 0, i_val = 0 ; i_bit < 8 ; ++i_bit )
{
i_lfsr0_o = ( ( i_lfsr0 >> 24 ) ^ ( i_lfsr0 >> 21 ) ^
( i_lfsr0 >> 20 ) ^ ( i_lfsr0 >> 12 ) ) & 1;
i_lfsr0 = ( i_lfsr0 << 1 ) | i_lfsr0_o;
i_lfsr1_o = ( ( i_lfsr1 >> 16 ) ^ ( i_lfsr1 >> 2 ) ) & 1;
i_lfsr1 = ( i_lfsr1 << 1 ) | i_lfsr1_o;
i_combined = !i_lfsr1_o + i_carry + !i_lfsr0_o;
/* taking bit 1 */
i_carry = ( i_combined >> 1 ) & 1;
i_val |= ( i_combined & 1 ) << i_bit;
}
p_bits[--i_index] = i_val;
} while( i_index > 0 );
/* This term is used throughout the following to
* select one of 32 different variations on the
* algorithm.
*/
i_cse = p_varients[i_css_varient] ^ p_crypt_tab2[i_css_varient];
/* Now the actual blocks doing the encryption. Each
* of these works on 40 bits at a time and are quite
* similar.
*/
i_index = 0;
for( i = 5, i_term = 0 ; --i >= 0 ; i_term = p_scratch[i] )
{
i_index = p_bits[25 + i] ^ p_scratch[i];
i_index = p_crypt_tab1[i_index] ^ ~p_crypt_tab2[i_index] ^ i_cse;
p_tmp1[i] = p_crypt_tab2[i_index] ^ p_crypt_tab3[i_index] ^ i_term;
}
p_tmp1[4] ^= p_tmp1[0];
for( i = 5, i_term = 0 ; --i >= 0 ; i_term = p_tmp1[i] )
{
i_index = p_bits[20 + i] ^ p_tmp1[i];
i_index = p_crypt_tab1[i_index] ^ ~p_crypt_tab2[i_index] ^ i_cse;
p_tmp2[i] = p_crypt_tab2[i_index] ^ p_crypt_tab3[i_index] ^ i_term;
}
p_tmp2[4] ^= p_tmp2[0];
for( i = 5, i_term = 0 ; --i >= 0 ; i_term = p_tmp2[i] )
{
i_index = p_bits[15 + i] ^ p_tmp2[i];
i_index = p_crypt_tab1[i_index] ^ ~p_crypt_tab2[i_index] ^ i_cse;
i_index = p_crypt_tab2[i_index] ^ p_crypt_tab3[i_index] ^ i_term;
p_tmp1[i] = p_crypt_tab0[i_index] ^ p_crypt_tab2[i_index];
}
p_tmp1[4] ^= p_tmp1[0];
for( i = 5, i_term = 0 ; --i >= 0 ; i_term = p_tmp1[i] )
{
i_index = p_bits[10 + i] ^ p_tmp1[i];
i_index = p_crypt_tab1[i_index] ^ ~p_crypt_tab2[i_index] ^ i_cse;
i_index = p_crypt_tab2[i_index] ^ p_crypt_tab3[i_index] ^ i_term;
p_tmp2[i] = p_crypt_tab0[i_index] ^ p_crypt_tab2[i_index];
}
p_tmp2[4] ^= p_tmp2[0];
for( i = 5, i_term = 0 ; --i >= 0 ; i_term = p_tmp2[i] )
{
i_index = p_bits[5 + i] ^ p_tmp2[i];
i_index = p_crypt_tab1[i_index] ^ ~p_crypt_tab2[i_index] ^ i_cse;
p_tmp1[i] = p_crypt_tab2[i_index] ^ p_crypt_tab3[i_index] ^ i_term;
}
p_tmp1[4] ^= p_tmp1[0];
for(i = 5, i_term = 0 ; --i >= 0 ; i_term = p_tmp1[i] )
{
i_index = p_bits[i] ^ p_tmp1[i];
i_index = p_crypt_tab1[i_index] ^ ~p_crypt_tab2[i_index] ^ i_cse;
p_key[i] = p_crypt_tab2[i_index] ^ p_crypt_tab3[i_index] ^ i_term;
}
return;
}
/*****************************************************************************
* CSSCracker : title key decryption by cracking
*****************************************************************************
* This function is called by CSSGetKeys to find a key
*****************************************************************************/
static int CSSCracker( int i_start,
unsigned char * p_crypted,
unsigned char * p_decrypted,
dvd_key_t * p_sector_key,
dvd_key_t * p_key )
{
unsigned char p_buffer[10];
unsigned int i_t1, i_t2, i_t3, i_t4, i_t5, i_t6;
unsigned int i_try;
unsigned int i_candidate;
unsigned int i, j;
int i_exit = -1;
for( i = 0 ; i < 10 ; i++ )
{
p_buffer[i] = p_css_tab1[p_crypted[i]] ^ p_decrypted[i];
}
for( i_try = i_start ; i_try < 0x10000 ; i_try++ )
{
i_t1 = i_try >> 8 | 0x100;
i_t2 = i_try & 0xff;
i_t3 = 0; /* not needed */
i_t5 = 0;
/* iterate cipher 4 times to reconstruct LFSR2 */
for( i = 0 ; i < 4 ; i++ )
{
/* advance LFSR1 normaly */
i_t4 = p_css_tab2[i_t2] ^ p_css_tab3[i_t1];
i_t2 = i_t1 >> 1;
i_t1 = ( ( i_t1 & 1 ) << 8 ) ^ i_t4;
i_t4 = p_css_tab5[i_t4];
/* deduce i_t6 & i_t5 */
i_t6 = p_buffer[i];
if( i_t5 )
{
i_t6 = ( i_t6 + 0xff ) & 0x0ff;
}
if( i_t6 < i_t4 )
{
i_t6 += 0x100;
}
i_t6 -= i_t4;
i_t5 += i_t6 + i_t4;
i_t6 = p_css_tab4[ i_t6 ];
/* feed / advance i_t3 / i_t5 */
i_t3 = ( i_t3 << 8 ) | i_t6;
i_t5 >>= 8;
}
i_candidate = i_t3;
/* iterate 6 more times to validate candidate key */
for( ; i < 10 ; i++ )
{
i_t4 = p_css_tab2[i_t2] ^ p_css_tab3[i_t1];
i_t2 = i_t1 >> 1;
i_t1 = ( ( i_t1 & 1 ) << 8 ) ^ i_t4;
i_t4 = p_css_tab5[i_t4];
i_t6 = ((((((( i_t3 >> 3 ) ^ i_t3 ) >> 1 ) ^
i_t3 ) >> 8 ) ^ i_t3 ) >> 5 ) & 0xff;
i_t3 = ( i_t3 << 8 ) | i_t6;
i_t6 = p_css_tab4[i_t6];
i_t5 += i_t6 + i_t4;
if( ( i_t5 & 0xff ) != p_buffer[i] )
{
break;
}
i_t5 >>= 8;
}
if( i == 10 )
{
/* Do 4 backwards steps of iterating t3 to deduce initial state */
i_t3 = i_candidate;
for( i = 0 ; i < 4 ; i++ )
{
i_t1 = i_t3 & 0xff;
i_t3 = ( i_t3 >> 8 );
/* easy to code, and fast enough bruteforce
* search for byte shifted in */
for( j = 0 ; j < 256 ; j++ )
{
i_t3 = ( i_t3 & 0x1ffff) | ( j << 17 );
i_t6 = ((((((( i_t3 >> 3 ) ^ i_t3 ) >> 1 ) ^
i_t3 ) >> 8 ) ^ i_t3 ) >> 5 ) & 0xff;
if( i_t6 == i_t1 )
{
break;
}
}
}
i_t4 = ( i_t3 >> 1 ) - 4;
for( i_t5 = 0 ; i_t5 < 8; i_t5++ )
{
if( ( ( i_t4 + i_t5 ) * 2 + 8 - ( (i_t4 + i_t5 ) & 7 ) )
== i_t3 )
{
(*p_key)[0] = i_try>>8;
(*p_key)[1] = i_try & 0xFF;
(*p_key)[2] = ( ( i_t4 + i_t5 ) >> 0) & 0xFF;
(*p_key)[3] = ( ( i_t4 + i_t5 ) >> 8) & 0xFF;
(*p_key)[4] = ( ( i_t4 + i_t5 ) >> 16) & 0xFF;
i_exit = i_try + 1;
}
}
}
}
if( i_exit >= 0 )
{
(*p_key)[0] ^= (*p_sector_key)[0];
(*p_key)[1] ^= (*p_sector_key)[1];
(*p_key)[2] ^= (*p_sector_key)[2];
(*p_key)[3] ^= (*p_sector_key)[3];
(*p_key)[4] ^= (*p_sector_key)[4];
}
return i_exit;
}
#endif /* HAVE_CSS */