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GCHQ CanYouCrackIt Stage 2 - PHP VM Implementation

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  1. <?php
  2. // Dr Gareth Owen, School of Engineering, University of Greenwich
  3. // GCHQ CanYouCrackIt Stage 2 solution
  4. // http://gchqchallenge.blogspot.com
  5. // To run: php vm.php
  6. // Enable $disasm flag to enable disassembly mode
  7.  
  8. $ip = 0;
  9. define( 'CS', 4);
  10. define( 'DS', 5);
  11. $gregs = array(0,0,0,0,0,0x10); // r0,1,2,3, cs, ds
  12. // flag reg
  13. $fl = 0;
  14.  
  15. //data
  16. $mem = array(0x31, 0x04, 0x33, 0xaa, 0x40, 0x02, 0x80, 0x03, 0x52, 0x00, 0x72, 0x01, 0x73, 0x01, 0xb2, 0x50,0x30, 0x14, 0xc0, 0x01, 0x80, 0x00, 0x10, 0x10, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,0x98, 0xab, 0xd9, 0xa1, 0x9f, 0xa7, 0x83, 0x83, 0xf2, 0xb1, 0x34, 0xb6, 0xe4, 0xb7, 0xca, 0xb8,0xc9, 0xb8, 0x0e, 0xbd, 0x7d, 0x0f, 0xc0, 0xf1, 0xd9, 0x03, 0xc5, 0x3a, 0xc6, 0xc7, 0xc8, 0xc9,0xca, 0xcb, 0xcc, 0xcd, 0xce, 0xcf, 0xd0, 0xd1, 0xd2, 0xd3, 0xd4, 0xd5, 0xd6, 0xd7, 0xd8, 0xd9,0xda, 0xdb, 0xa9, 0xcd, 0xdf, 0xdf, 0xe0, 0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7, 0xe8, 0xe9,0x26, 0xeb, 0xec, 0xed, 0xee, 0xef, 0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8, 0xf9,0x7d, 0x1f, 0x15, 0x60, 0x4d, 0x4d, 0x52, 0x7d, 0x0e, 0x27, 0x6d, 0x10, 0x6d, 0x5a, 0x06, 0x56,0x47, 0x14, 0x42, 0x0e, 0xb6, 0xb2, 0xb2, 0xe6, 0xeb, 0xb4, 0x83, 0x8e, 0xd7, 0xe5, 0xd4, 0xd9,0xc3, 0xf0, 0x80, 0x95, 0xf1, 0x82, 0x82, 0x9a, 0xbd, 0x95, 0xa4, 0x8d, 0x9a, 0x2b, 0x30, 0x69,0x4a, 0x69, 0x65, 0x55, 0x1c, 0x7b, 0x69, 0x1c, 0x6e, 0x04, 0x74, 0x35, 0x21, 0x26, 0x2f, 0x60,0x03, 0x4e, 0x37, 0x1e, 0x33, 0x54, 0x39, 0xe6, 0xba, 0xb4, 0xa2, 0xad, 0xa4, 0xc5, 0x95, 0xc8,0xc1, 0xe4, 0x8a, 0xec, 0xe7, 0x92, 0x8b, 0xe8, 0x81, 0xf0, 0xad, 0x98, 0xa4, 0xd0, 0xc0, 0x8d,0xac, 0x22, 0x52, 0x65, 0x7e, 0x27, 0x2b, 0x5a, 0x12, 0x61, 0x0a, 0x01, 0x7a, 0x6b, 0x1d, 0x67,0x75, 0x70, 0x6c, 0x1b, 0x11, 0x25, 0x25, 0x70, 0x7f, 0x7e, 0x67, 0x63, 0x30, 0x3c, 0x6d, 0x6a,0x01, 0x51, 0x59, 0x5f, 0x56, 0x13, 0x10, 0x43, 0x19, 0x18, 0xe5, 0xe0, 0xbe, 0xbf, 0xbd, 0xe9,0xf0, 0xf1, 0xf9, 0xfa, 0xab, 0x8f, 0xc1, 0xdf, 0xcf, 0x8d, 0xf8, 0xe7, 0xe2, 0xe9, 0x93, 0x8e,0xec, 0xf5, 0xc8, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,0x37, 0x7a, 0x07, 0x11, 0x1f, 0x1d, 0x68, 0x25, 0x32, 0x77, 0x1e, 0x62, 0x23, 0x5b, 0x47, 0x55,0x53, 0x30, 0x11, 0x42, 0xf6, 0xf1, 0xb1, 0xe6, 0xc3, 0xcc, 0xf8, 0xc5, 0xe4, 0xcc, 0xc0, 0xd3,0x85, 0xfd, 0x9a, 0xe3, 0xe6, 0x81, 0xb5, 0xbb, 0xd7, 0xcd, 0x87, 0xa3, 0xd3, 0x6b, 0x36, 0x6f,0x6f, 0x66, 0x55, 0x30, 0x16, 0x45, 0x5e, 0x09, 0x74, 0x5c, 0x3f, 0x29, 0x2b, 0x66, 0x3d, 0x0d,0x02, 0x30, 0x28, 0x35, 0x15, 0x09, 0x15, 0xdd, 0xec, 0xb8, 0xe2, 0xfb, 0xd8, 0xcb, 0xd8, 0xd1,0x8b, 0xd5, 0x82, 0xd9, 0x9a, 0xf1, 0x92, 0xab, 0xe8, 0xa6, 0xd6, 0xd0, 0x8c, 0xaa, 0xd2, 0x94,0xcf, 0x45, 0x46, 0x67, 0x20, 0x7d, 0x44, 0x14, 0x6b, 0x45, 0x6d, 0x54, 0x03, 0x17, 0x60, 0x62,0x55, 0x5a, 0x4a, 0x66, 0x61, 0x11, 0x57, 0x68, 0x75, 0x05, 0x62, 0x36, 0x7d, 0x02, 0x10, 0x4b,0x08, 0x22, 0x42, 0x32, 0xba, 0xe2, 0xb9, 0xe2, 0xd6, 0xb9, 0xff, 0xc3, 0xe9, 0x8a, 0x8f, 0xc1,0x8f, 0xe1, 0xb8, 0xa4, 0x96, 0xf1, 0x8f, 0x81, 0xb1, 0x8d, 0x89, 0xcc, 0xd4, 0x78, 0x76, 0x61,0x72, 0x3e, 0x37, 0x23, 0x56, 0x73, 0x71, 0x79, 0x63, 0x7c, 0x08, 0x11, 0x20, 0x69, 0x7a, 0x14,0x68, 0x05, 0x21, 0x1e, 0x32, 0x27, 0x59, 0xb7, 0xcf, 0xab, 0xdd, 0xd5, 0xcc, 0x97, 0x93, 0xf2,0xe7, 0xc0, 0xeb, 0xff, 0xe9, 0xa3, 0xbf, 0xa1, 0xab, 0x8b, 0xbb, 0x9e, 0x9e, 0x8c, 0xa0, 0xc1,0x9b, 0x5a, 0x2f, 0x2f, 0x4e, 0x4e, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00);
  17.  
  18. dump('initial');
  19.  
  20. // instructions
  21. $instr = array('jmp', 'movr', 'movm', 'add', 'xor', 'cmp', 'jmpe', 'hlt');
  22.  
  23. // dump array on single line
  24. function da($nm, $arr) {
  25.   echo "$nm=(";
  26.   foreach($arr as $a)
  27.     echo "$a,";
  28.   echo ") ";
  29. }
  30.  
  31. $disasm = 0;
  32. $first = 0;
  33. // main loop
  34. while(1) {
  35.   if($disasm && $ip > 15) { $gregs[CS]++; $ip %= 16; }
  36.   $i = $gregs[CS] * 16 + $ip;
  37.  
  38. /*if($i == 0x10e && $first == 0) {
  39.   $ip += 4;//0x112;
  40.   $first = 1;
  41. }*//*if($i > 0x100) $disasm = 1;*/
  42.  
  43. // ofset print
  44.   printf("0x%x [%x:%x]", $i, $gregs[CS], $ip);
  45.   echo "{$gregs[CS]}:$ip "; // mem location
  46.  
  47.  
  48.   $tmpreg = $gregs;
  49.  
  50.   // out of memory
  51.   if($i>count($mem)) { echo "oob $i\n";  exit(0); }
  52.  
  53.   $b = $mem[$i];
  54.   $opcode = ($b & 0xE0) >> 5;
  55.   $mod = ($b & 0x10) >> 4;
  56.   $op1 = ($b & 0x0F);
  57.   $op2 = $mem[$i+1];
  58.   $bytes = 1;
  59.  
  60. // instruction stat
  61.   if(!$disasm) {
  62.     echo "{$instr[$opcode]} (m=$mod, op1=$op1, op2=$op2) ";
  63.     da('r*', $gregs);
  64.     echo " fl=$fl ";
  65.   }
  66.  
  67.   $noadv = 0; // dont advance IP (for jumps)
  68.   switch($opcode) {
  69.     case 0: // jmp
  70.       if(!$disasm)
  71.         $ip = $gregs[$op1];
  72.  
  73.       if($mod == 1) {
  74.         if(!$disasm)
  75.           $gregs[CS] = $op2;
  76.         echo "jmp $op2:r$op1\n";
  77.         $bytes ++;
  78.       } else echo "jmp r$op1\n";
  79.       $noadv = 1;
  80.       break;
  81.     case 1: // movr
  82.       $bytes++;
  83.       if($mod == 0)  {
  84.         $gregs[$op1] = $gregs[$op2];
  85.         echo "movr r$op1, r$op2\n";
  86.       }
  87.       else {
  88.         echo "movr r$op1, $op2\n";
  89.         $gregs[$op1] = $op2;
  90.       }
  91.       break;
  92.     case 2: // movm
  93.       $bytes++;
  94.       if($mod == 0) {
  95.         $gregs[$op1] = $mem[$gregs[DS]*16 + $gregs[$op2]];
  96.         echo "movm r$op1, [ds:r$op2]\n";
  97.         if(!$disasm) echo "{$gregs[$op1]} <= [{$gregs[DS]}:{$gregs[$op2]}] {$mem[$gregs[DS]*16 + $gregs[$op2]]}";
  98.       }
  99.       else {
  100.         $mem[$gregs[DS]*16 + $gregs[$op1]] = $gregs[$op2];
  101.         echo "movm [ds:r$op1], r$op2\n";
  102.         if(!$disasm) echo "[{$gregs[DS]}:{$gregs[$op1]}] {$mem[$gregs[DS]*16 + $gregs[$op1]]} <= {$gregs[$op2]}";
  103.       }
  104.      
  105.       break;
  106.     case 3: // add
  107.       $bytes++;
  108.       if($mod == 0) {
  109.         $gregs[$op1] = ($gregs[$op1] + $gregs[$op2]) & 0xFF;
  110.         echo "add r$op1, r$op2\n";
  111.       }
  112.       else {
  113.         $gregs[$op1] = ($gregs[$op1] + $op2) & 0xFF;
  114.         echo "add r$op1, $op2\n";
  115.       }
  116.       break;
  117.     case 4: // xor
  118.       $bytes++;
  119.       if($mod == 0) {
  120.         $gregs[$op1] ^= $gregs[$op2];
  121.         echo "xor r$op1, r$op2\n";
  122.       }
  123.       else{
  124.         $gregs[$op1] ^= $op2;
  125.         echo "xor r$op1, $op2\n";
  126.       }
  127.       break;
  128.     case 5: // cmp
  129.       $bytes++;
  130.       if($mod == 0)
  131.       {
  132.         if($gregs[$op1] == $gregs[$op2]) $fl = 0;
  133.         else if($gregs[$op1] < $gregs[$op2]) $fl = 0xff;
  134.         else $fl = 1;
  135.         echo "cmp r$op1, r$op2\n";
  136.       }
  137.       else
  138.       {
  139.         if($gregs[$op1] == $op2) $fl = 0;
  140.         else if($gregs[$op1] < $op2) $fl = 0xff;
  141.         else $fl = 1;
  142.         echo "cmp r$op1, $op2\n";
  143.       }
  144.       break;
  145.     case 6: // jmpe
  146.       if($fl == 0 || $disasm) {
  147.         if(!$disasm)
  148.           $ip = $gregs[$op1];
  149.         $noadv = 1;
  150.         if($mod != 0) {
  151.           $bytes++;
  152.           if(!$disasm)
  153.             $gregs[CS] = $op2;
  154.           echo "jmpe $op2:r$op1\n";
  155.         } else echo "jmpe r$op1\n";
  156.       }
  157.       break;
  158.     case 7: // hlt
  159.       echo "hlt\n";
  160.       if(!$disasm) {
  161.         dump();
  162.         exit(0);
  163.       }
  164.       break;
  165.     default:
  166.       echo "invalid\n";
  167.   }
  168.  
  169.   if($disasm)
  170.     $gregs=$tmpreg;
  171.  
  172.   if(!$noadv || $disasm)
  173.     $ip+=$bytes;
  174.   if(!$disasm)
  175.     echo "\n";
  176. }
  177.  
  178. function dump($f = "dump.bin") {
  179.   global $mem;
  180.   $o = fopen($f, "wb");
  181.   foreach($mem as $m)
  182.     fputs($o, chr($m));
  183.   fclose($o);
  184.   echo "dumped\n";
  185. }
  186.  
  187.  
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