1 /*****************************************************************************
2 * css.c: Functions for DVD authentification and unscrambling
3 *****************************************************************************
4 * Copyright (C) 1999-2001 VideoLAN
5 * $Id: css.c,v 1.8 2001/08/06 13:27:59 sam Exp $
7 * Author: Stéphane Borel <stef@via.ecp.fr>
10 * - css-auth by Derek Fawcus <derek@spider.com>
11 * - DVD CSS ioctls example program by Andrew T. Veliath <andrewtv@usa.net>
12 * - The Divide and conquer attack by Frank A. Stevenson <frank@funcom.com>
13 * - DeCSSPlus by Ethan Hawke
15 * see http://www.lemuria.org/DeCSS/ by Tom Vogt for more information.
17 * This program is free software; you can redistribute it and/or modify
18 * it under the terms of the GNU General Public License as published by
19 * the Free Software Foundation; either version 2 of the License, or
20 * (at your option) any later version.
22 * This program is distributed in the hope that it will be useful,
23 * but WITHOUT ANY WARRANTY; without even the implied warranty of
24 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
25 * GNU General Public License for more details.
27 * You should have received a copy of the GNU General Public License
28 * along with this program; if not, write to the Free Software
29 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111, USA.
30 *****************************************************************************/
32 /*****************************************************************************
34 *****************************************************************************/
45 #include "videolan/dvdcss.h"
46 #include "libdvdcss.h"
48 #include "csstables.h"
51 /*****************************************************************************
53 *****************************************************************************/
54 static int CSSGetASF ( dvdcss_handle dvdcss );
55 static void CSSCryptKey ( int i_key_type, int i_varient,
56 u8 const * p_challenge, u8* p_key );
57 static int CSSCracker ( int i_start, unsigned char * p_crypted,
58 unsigned char * p_decrypted,
59 dvd_key_t * p_sector_key, dvd_key_t * p_key );
61 /*****************************************************************************
62 * CSSTest : check if the disc is encrypted or not
63 *****************************************************************************/
64 int CSSTest( dvdcss_handle dvdcss )
66 int i_ret, i_copyright;
68 i_ret = ioctl_ReadCopyright( dvdcss->i_fd, 0 /* i_layer */, &i_copyright );
72 /* Since it's the first ioctl we try to issue, we add a notice */
73 _dvdcss_error( dvdcss, "css error: ioctl_ReadCopyright failed, "
74 "make sure DVD ioctls were compiled in" );
82 /*****************************************************************************
83 * CSSInit : CSS Structure initialisation and DVD authentication.
84 *****************************************************************************
85 * It simulates the mutual authentication between logical unit and host.
86 * Since we don't need the disc key to find the title key, we just run the
87 * basic unavoidable commands to authenticate device and disc.
88 *****************************************************************************/
89 int CSSInit( dvdcss_handle dvdcss )
91 /* structures defined in cdrom.h or dvdio.h */
92 unsigned char p_buffer[2048 + 4 + 1];
98 /* Test authentication success */
99 switch( CSSGetASF( dvdcss ) )
105 _dvdcss_debug( dvdcss, "already authenticated" );
109 _dvdcss_debug( dvdcss, "need to authenticate" );
112 /* Init sequence, request AGID */
113 for( i = 1; i < 4 ; ++i )
115 sprintf( psz_warning, "requesting AGID %d", i );
116 _dvdcss_debug( dvdcss, psz_warning );
118 i_ret = ioctl_ReportAgid( dvdcss->i_fd, &i_agid );
122 /* No error during ioctl: we know the device is authenticated */
126 _dvdcss_error( dvdcss, "ioctl_ReportAgid failed, invalidating" );
129 ioctl_InvalidateAgid( dvdcss->i_fd, &i_agid );
132 /* Unable to authenticate without AGID */
135 _dvdcss_error( dvdcss, "ioctl_ReportAgid failed, fatal" );
139 for( i = 0 ; i < 10; ++i )
141 dvdcss->css.disc.p_challenge[i] = i;
144 /* Get challenge from host */
145 for( i = 0 ; i < 10 ; ++i )
147 p_buffer[9-i] = dvdcss->css.disc.p_challenge[i];
150 /* Send challenge to LU */
151 if( ioctl_SendChallenge( dvdcss->i_fd, &i_agid, p_buffer ) < 0 )
153 _dvdcss_error( dvdcss, "ioctl_SendChallenge failed" );
157 /* Get key1 from LU */
158 if( ioctl_ReportKey1( dvdcss->i_fd, &i_agid, p_buffer ) < 0)
160 _dvdcss_error( dvdcss, "ioctl_ReportKey1 failed" );
164 /* Send key1 to host */
165 for( i = 0 ; i < KEY_SIZE ; i++ )
167 dvdcss->css.disc.p_key1[i] = p_buffer[4-i];
170 for( i = 0 ; i < 32 ; ++i )
172 CSSCryptKey( 0, i, dvdcss->css.disc.p_challenge,
173 dvdcss->css.disc.p_key_check );
175 if( memcmp( dvdcss->css.disc.p_key_check,
176 dvdcss->css.disc.p_key1, KEY_SIZE ) == 0 )
178 sprintf( psz_warning, "drive authentic, using variant %d", i );
179 _dvdcss_debug( dvdcss, psz_warning );
180 dvdcss->css.disc.i_varient = i;
187 _dvdcss_error( dvdcss, "drive would not authenticate" );
191 /* Get challenge from LU */
192 if( ioctl_ReportChallenge( dvdcss->i_fd, &i_agid, p_buffer ) < 0 )
194 _dvdcss_error( dvdcss, "ioctl_ReportKeyChallenge failed" );
198 /* Send challenge to host */
199 for( i = 0 ; i < 10 ; ++i )
201 dvdcss->css.disc.p_challenge[i] = p_buffer[9-i];
204 CSSCryptKey( 1, dvdcss->css.disc.i_varient,
205 dvdcss->css.disc.p_challenge,
206 dvdcss->css.disc.p_key2 );
208 /* Get key2 from host */
209 for( i = 0 ; i < KEY_SIZE ; ++i )
211 p_buffer[4-i] = dvdcss->css.disc.p_key2[i];
214 /* Send key2 to LU */
215 if( ioctl_SendKey2( dvdcss->i_fd, &i_agid, p_buffer ) < 0 )
217 _dvdcss_error( dvdcss, "ioctl_SendKey2 failed" );
221 _dvdcss_debug( dvdcss, "authentication established" );
223 memcpy( dvdcss->css.disc.p_challenge,
224 dvdcss->css.disc.p_key1, KEY_SIZE );
225 memcpy( dvdcss->css.disc.p_challenge+KEY_SIZE,
226 dvdcss->css.disc.p_key2, KEY_SIZE );
228 CSSCryptKey( 2, dvdcss->css.disc.i_varient,
229 dvdcss->css.disc.p_challenge,
230 dvdcss->css.disc.p_key_check );
232 _dvdcss_debug( dvdcss, "received session key" );
239 /* Test authentication success */
240 switch( CSSGetASF( dvdcss ) )
246 _dvdcss_debug( dvdcss, "already authenticated" );
250 _dvdcss_debug( dvdcss, "need to get disc key" );
253 /* Get encrypted disc key */
254 if( ioctl_ReadKey( dvdcss->i_fd, &i_agid, p_buffer ) < 0 )
256 _dvdcss_error( dvdcss, "ioctl_ReadKey failed" );
260 /* Unencrypt disc key using bus key */
261 for( i = 0 ; i < 2048 ; i++ )
263 p_buffer[ i ] ^= dvdcss->css.disc.p_key_check[ 4 - (i % KEY_SIZE) ];
265 memcpy( dvdcss->css.disc.p_key_check, p_buffer, 2048 );
267 /* Test authentication success */
268 switch( CSSGetASF( dvdcss ) )
274 _dvdcss_debug( dvdcss, "successfully authenticated" );
278 _dvdcss_error( dvdcss, "no way to authenticate" );
285 /*****************************************************************************
286 * CSSGetKey : get title key.
287 *****************************************************************************
288 * The DVD should have been opened and authenticated before.
289 *****************************************************************************/
290 int CSSGetKey( dvdcss_handle dvdcss, int i_pos, dvd_key_t p_titlekey )
293 * Title key cracking method from Ethan Hawke,
294 * with Frank A. Stevenson algorithm.
295 * Does not use any player key table and ioctls.
299 boolean_t b_encrypted;
300 boolean_t b_stop_scanning;
306 for( i = 0 ; i < KEY_SIZE ; i++ )
316 i_pos = dvdcss_seek( dvdcss, i_pos );
317 i_blocks_read = dvdcss_read( dvdcss, p_buf, 1, DVDCSS_NOFLAGS );
319 /* PES_scrambling_control */
320 if( p_buf[0x14] & 0x30 )
326 for( i = 2 ; i < 0x30 ; i++ )
329 j < 0x80 && ( p_buf[0x7F - (j%i)] == p_buf[0x7F-j] );
332 if( j > i_best_plen )
340 if( ( i_best_plen > 20 ) && ( i_best_plen / i_best_p >= 2) )
342 i = CSSCracker( 0, &p_buf[0x80],
343 &p_buf[0x80 - ( i_best_plen / i_best_p) *i_best_p],
344 (dvd_key_t*)&p_buf[0x54],
346 b_stop_scanning = ( i >= 0 );
350 i_pos += i_blocks_read;
352 } while( i_blocks_read == 0x1 && !b_stop_scanning );
354 if( b_stop_scanning )
356 memcpy( p_titlekey, &p_key, sizeof(dvd_key_t) );
357 _dvdcss_debug( dvdcss, "vts key initialized" );
363 _dvdcss_debug( dvdcss, "file was unscrambled" );
370 /*****************************************************************************
371 * CSSDescrambleSector
372 *****************************************************************************
373 * sec : sector to descramble
374 * key : title key for this sector
375 *****************************************************************************/
376 int CSSDescrambleSector( dvd_key_t p_key, u8* p_sec )
378 unsigned int i_t1, i_t2, i_t3, i_t4, i_t5, i_t6;
379 u8* p_end = p_sec + 0x800;
381 /* PES_scrambling_control */
382 if( p_sec[0x14] & 0x30)
384 i_t1 = ((p_key)[0] ^ p_sec[0x54]) | 0x100;
385 i_t2 = (p_key)[1] ^ p_sec[0x55];
386 i_t3 = (((p_key)[2]) | ((p_key)[3] << 8) |
387 ((p_key)[4] << 16)) ^ ((p_sec[0x56]) |
388 (p_sec[0x57] << 8) | (p_sec[0x58] << 16));
390 i_t3 = i_t3 * 2 + 8 - i_t4;
394 while( p_sec != p_end )
396 i_t4 = p_css_tab2[i_t2] ^ p_css_tab3[i_t1];
398 i_t1 = ( ( i_t1 & 1 ) << 8 ) ^ i_t4;
399 i_t4 = p_css_tab5[i_t4];
400 i_t6 = ((((((( i_t3 >> 3 ) ^ i_t3 ) >> 1 ) ^
401 i_t3 ) >> 8 ) ^ i_t3 ) >> 5) & 0xff;
402 i_t3 = (i_t3 << 8 ) | i_t6;
403 i_t6 = p_css_tab4[i_t6];
405 *p_sec = p_css_tab1[*p_sec] ^( i_t5 & 0xff );
414 /* Following functions are local */
416 /*****************************************************************************
417 * CSSGetASF : Get Authentification success flag
418 *****************************************************************************
421 * 0 if the device needs to be authenticated,
423 *****************************************************************************/
424 static int CSSGetASF( dvdcss_handle dvdcss )
429 for( i_agid = 0 ; i_agid < 4 ; i_agid++ )
431 if( ioctl_ReportASF( dvdcss->i_fd, &i_agid, &i_asf ) == 0 )
435 _dvdcss_debug( dvdcss, "GetASF authenticated" );
439 _dvdcss_debug( dvdcss, "GetASF not authenticated" );
446 /* The ioctl process has failed */
447 _dvdcss_error( dvdcss, "GetASF fatal error" );
451 /*****************************************************************************
452 * CSSCryptKey : shuffles bits and unencrypt keys.
453 *****************************************************************************
454 * Used during authentication and disc key negociation in CSSInit.
455 * i_key_type : 0->key1, 1->key2, 2->buskey.
456 * i_varient : between 0 and 31.
457 *****************************************************************************/
458 static void CSSCryptKey( int i_key_type, int i_varient,
459 u8 const * p_challenge, u8* p_key )
461 /* Permutation table for challenge */
462 u8 pp_perm_challenge[3][10] =
463 { { 1, 3, 0, 7, 5, 2, 9, 6, 4, 8 },
464 { 6, 1, 9, 3, 8, 5, 7, 4, 0, 2 },
465 { 4, 0, 3, 5, 7, 2, 8, 6, 1, 9 } };
467 /* Permutation table for varient table for key2 and buskey */
468 u8 pp_perm_varient[2][32] =
469 { { 0x0a, 0x08, 0x0e, 0x0c, 0x0b, 0x09, 0x0f, 0x0d,
470 0x1a, 0x18, 0x1e, 0x1c, 0x1b, 0x19, 0x1f, 0x1d,
471 0x02, 0x00, 0x06, 0x04, 0x03, 0x01, 0x07, 0x05,
472 0x12, 0x10, 0x16, 0x14, 0x13, 0x11, 0x17, 0x15 },
473 { 0x12, 0x1a, 0x16, 0x1e, 0x02, 0x0a, 0x06, 0x0e,
474 0x10, 0x18, 0x14, 0x1c, 0x00, 0x08, 0x04, 0x0c,
475 0x13, 0x1b, 0x17, 0x1f, 0x03, 0x0b, 0x07, 0x0f,
476 0x11, 0x19, 0x15, 0x1d, 0x01, 0x09, 0x05, 0x0d } };
479 { 0xB7, 0x74, 0x85, 0xD0, 0xCC, 0xDB, 0xCA, 0x73,
480 0x03, 0xFE, 0x31, 0x03, 0x52, 0xE0, 0xB7, 0x42,
481 0x63, 0x16, 0xF2, 0x2A, 0x79, 0x52, 0xFF, 0x1B,
482 0x7A, 0x11, 0xCA, 0x1A, 0x9B, 0x40, 0xAD, 0x01 };
484 /* The "secret" key */
485 u8 p_secret[5] = { 0x55, 0xD6, 0xC4, 0xC5, 0x28 };
491 u8 i_lfsr0_o; /* 1 bit used */
492 u8 i_lfsr1_o; /* 1 bit used */
505 for (i = 9; i >= 0; --i)
506 p_scratch[i] = p_challenge[pp_perm_challenge[i_key_type][i]];
508 i_css_varient = ( i_key_type == 0 ) ? i_varient :
509 pp_perm_varient[i_key_type-1][i_varient];
512 * This encryption engine implements one of 32 variations
513 * one the same theme depending upon the choice in the
514 * varient parameter (0 - 31).
516 * The algorithm itself manipulates a 40 bit input into
518 * The parameter 'input' is 80 bits. It consists of
519 * the 40 bit input value that is to be encrypted followed
520 * by a 40 bit seed value for the pseudo random number
524 /* Feed the secret into the input values such that
525 * we alter the seed to the LFSR's used above, then
526 * generate the bits to play with.
528 for( i = 5 ; --i >= 0 ; )
530 p_tmp1[i] = p_scratch[5 + i] ^ p_secret[i] ^ p_crypt_tab2[i];
534 * We use two LFSR's (seeded from some of the input data bytes) to
535 * generate two streams of pseudo-random bits. These two bit streams
536 * are then combined by simply adding with carry to generate a final
537 * sequence of pseudo-random bits which is stored in the buffer that
538 * 'output' points to the end of - len is the size of this buffer.
540 * The first LFSR is of degree 25, and has a polynomial of:
541 * x^13 + x^5 + x^4 + x^1 + 1
543 * The second LSFR is of degree 17, and has a (primitive) polynomial of:
546 * I don't know if these polynomials are primitive modulo 2, and thus
547 * represent maximal-period LFSR's.
550 * Note that we take the output of each LFSR from the new shifted in
551 * bit, not the old shifted out bit. Thus for ease of use the LFSR's
552 * are implemented in bit reversed order.
556 /* In order to ensure that the LFSR works we need to ensure that the
557 * initial values are non-zero. Thus when we initialise them from
558 * the seed, we ensure that a bit is set.
560 i_lfsr0 = ( p_tmp1[0] << 17 ) | ( p_tmp1[1] << 9 ) |
561 (( p_tmp1[2] & ~7 ) << 1 ) | 8 | ( p_tmp1[2] & 7 );
562 i_lfsr1 = ( p_tmp1[3] << 9 ) | 0x100 | p_tmp1[4];
564 i_index = sizeof(p_bits);
569 for( i_bit = 0, i_val = 0 ; i_bit < 8 ; ++i_bit )
572 i_lfsr0_o = ( ( i_lfsr0 >> 24 ) ^ ( i_lfsr0 >> 21 ) ^
573 ( i_lfsr0 >> 20 ) ^ ( i_lfsr0 >> 12 ) ) & 1;
574 i_lfsr0 = ( i_lfsr0 << 1 ) | i_lfsr0_o;
576 i_lfsr1_o = ( ( i_lfsr1 >> 16 ) ^ ( i_lfsr1 >> 2 ) ) & 1;
577 i_lfsr1 = ( i_lfsr1 << 1 ) | i_lfsr1_o;
579 i_combined = !i_lfsr1_o + i_carry + !i_lfsr0_o;
581 i_carry = ( i_combined >> 1 ) & 1;
582 i_val |= ( i_combined & 1 ) << i_bit;
585 p_bits[--i_index] = i_val;
586 } while( i_index > 0 );
588 /* This term is used throughout the following to
589 * select one of 32 different variations on the
592 i_cse = p_varients[i_css_varient] ^ p_crypt_tab2[i_css_varient];
594 /* Now the actual blocks doing the encryption. Each
595 * of these works on 40 bits at a time and are quite
599 for( i = 5, i_term = 0 ; --i >= 0 ; i_term = p_scratch[i] )
601 i_index = p_bits[25 + i] ^ p_scratch[i];
602 i_index = p_crypt_tab1[i_index] ^ ~p_crypt_tab2[i_index] ^ i_cse;
604 p_tmp1[i] = p_crypt_tab2[i_index] ^ p_crypt_tab3[i_index] ^ i_term;
606 p_tmp1[4] ^= p_tmp1[0];
608 for( i = 5, i_term = 0 ; --i >= 0 ; i_term = p_tmp1[i] )
610 i_index = p_bits[20 + i] ^ p_tmp1[i];
611 i_index = p_crypt_tab1[i_index] ^ ~p_crypt_tab2[i_index] ^ i_cse;
613 p_tmp2[i] = p_crypt_tab2[i_index] ^ p_crypt_tab3[i_index] ^ i_term;
615 p_tmp2[4] ^= p_tmp2[0];
617 for( i = 5, i_term = 0 ; --i >= 0 ; i_term = p_tmp2[i] )
619 i_index = p_bits[15 + i] ^ p_tmp2[i];
620 i_index = p_crypt_tab1[i_index] ^ ~p_crypt_tab2[i_index] ^ i_cse;
621 i_index = p_crypt_tab2[i_index] ^ p_crypt_tab3[i_index] ^ i_term;
623 p_tmp1[i] = p_crypt_tab0[i_index] ^ p_crypt_tab2[i_index];
625 p_tmp1[4] ^= p_tmp1[0];
627 for( i = 5, i_term = 0 ; --i >= 0 ; i_term = p_tmp1[i] )
629 i_index = p_bits[10 + i] ^ p_tmp1[i];
630 i_index = p_crypt_tab1[i_index] ^ ~p_crypt_tab2[i_index] ^ i_cse;
632 i_index = p_crypt_tab2[i_index] ^ p_crypt_tab3[i_index] ^ i_term;
634 p_tmp2[i] = p_crypt_tab0[i_index] ^ p_crypt_tab2[i_index];
636 p_tmp2[4] ^= p_tmp2[0];
638 for( i = 5, i_term = 0 ; --i >= 0 ; i_term = p_tmp2[i] )
640 i_index = p_bits[5 + i] ^ p_tmp2[i];
641 i_index = p_crypt_tab1[i_index] ^ ~p_crypt_tab2[i_index] ^ i_cse;
643 p_tmp1[i] = p_crypt_tab2[i_index] ^ p_crypt_tab3[i_index] ^ i_term;
645 p_tmp1[4] ^= p_tmp1[0];
647 for(i = 5, i_term = 0 ; --i >= 0 ; i_term = p_tmp1[i] )
649 i_index = p_bits[i] ^ p_tmp1[i];
650 i_index = p_crypt_tab1[i_index] ^ ~p_crypt_tab2[i_index] ^ i_cse;
652 p_key[i] = p_crypt_tab2[i_index] ^ p_crypt_tab3[i_index] ^ i_term;
658 /*****************************************************************************
659 * CSSCracker : title key decryption by cracking
660 *****************************************************************************
661 * This function is called by CSSGetKeys to find a key
662 *****************************************************************************/
663 static int CSSCracker( int i_start,
664 unsigned char * p_crypted,
665 unsigned char * p_decrypted,
666 dvd_key_t * p_sector_key,
669 unsigned char p_buffer[10];
670 unsigned int i_t1, i_t2, i_t3, i_t4, i_t5, i_t6;
672 unsigned int i_candidate;
677 for( i = 0 ; i < 10 ; i++ )
679 p_buffer[i] = p_css_tab1[p_crypted[i]] ^ p_decrypted[i];
682 for( i_try = i_start ; i_try < 0x10000 ; i_try++ )
684 i_t1 = i_try >> 8 | 0x100;
686 i_t3 = 0; /* not needed */
689 /* iterate cipher 4 times to reconstruct LFSR2 */
690 for( i = 0 ; i < 4 ; i++ )
692 /* advance LFSR1 normaly */
693 i_t4 = p_css_tab2[i_t2] ^ p_css_tab3[i_t1];
695 i_t1 = ( ( i_t1 & 1 ) << 8 ) ^ i_t4;
696 i_t4 = p_css_tab5[i_t4];
697 /* deduce i_t6 & i_t5 */
701 i_t6 = ( i_t6 + 0xff ) & 0x0ff;
709 i_t6 = p_css_tab4[ i_t6 ];
710 /* feed / advance i_t3 / i_t5 */
711 i_t3 = ( i_t3 << 8 ) | i_t6;
717 /* iterate 6 more times to validate candidate key */
718 for( ; i < 10 ; i++ )
720 i_t4 = p_css_tab2[i_t2] ^ p_css_tab3[i_t1];
722 i_t1 = ( ( i_t1 & 1 ) << 8 ) ^ i_t4;
723 i_t4 = p_css_tab5[i_t4];
724 i_t6 = ((((((( i_t3 >> 3 ) ^ i_t3 ) >> 1 ) ^
725 i_t3 ) >> 8 ) ^ i_t3 ) >> 5 ) & 0xff;
726 i_t3 = ( i_t3 << 8 ) | i_t6;
727 i_t6 = p_css_tab4[i_t6];
729 if( ( i_t5 & 0xff ) != p_buffer[i] )
739 /* Do 4 backwards steps of iterating t3 to deduce initial state */
741 for( i = 0 ; i < 4 ; i++ )
744 i_t3 = ( i_t3 >> 8 );
745 /* easy to code, and fast enough bruteforce
746 * search for byte shifted in */
747 for( j = 0 ; j < 256 ; j++ )
749 i_t3 = ( i_t3 & 0x1ffff) | ( j << 17 );
750 i_t6 = ((((((( i_t3 >> 3 ) ^ i_t3 ) >> 1 ) ^
751 i_t3 ) >> 8 ) ^ i_t3 ) >> 5 ) & 0xff;
759 i_t4 = ( i_t3 >> 1 ) - 4;
760 for( i_t5 = 0 ; i_t5 < 8; i_t5++ )
762 if( ( ( i_t4 + i_t5 ) * 2 + 8 - ( (i_t4 + i_t5 ) & 7 ) )
765 (*p_key)[0] = i_try>>8;
766 (*p_key)[1] = i_try & 0xFF;
767 (*p_key)[2] = ( ( i_t4 + i_t5 ) >> 0) & 0xFF;
768 (*p_key)[3] = ( ( i_t4 + i_t5 ) >> 8) & 0xFF;
769 (*p_key)[4] = ( ( i_t4 + i_t5 ) >> 16) & 0xFF;
778 (*p_key)[0] ^= (*p_sector_key)[0];
779 (*p_key)[1] ^= (*p_sector_key)[1];
780 (*p_key)[2] ^= (*p_sector_key)[2];
781 (*p_key)[3] ^= (*p_sector_key)[3];
782 (*p_key)[4] ^= (*p_sector_key)[4];