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  1. <?php
  2.  
  3. # Part II: Hardened Keyed Caesar
  4. # Example usage:
  5. # encrypt('Ciphers are hard!',array(1,2,3,4),3);
  6. # decrypt('GQBXULQCTKROFV',array(1,2,3,4),3);
  7. # Note the these functions are not strictly inverses of each other,
  8. # as the decryption function does not restore spaces or punctuation.
  9.  
  10. function encrypt($text, $key, $inc) {
  11. 	# Turn text to uppercase
  12. 	$text = strtoupper($text);
  13. 	# Remove spaces and punctuation
  14. 	$text = preg_replace('/[^A-Z]/','',$text);
  15. 	# Turn text into an array
  16. 	$text = str_split($text);
  17. 	# Turn text into numbers, A=0, ...Z=25
  18. 	$numbers = array();
  19. 	foreach($text as $letter) {
  20. 		$numbers[] = ord($letter) - 65;
  21. 	}
  22. 	# Apply the key:
  23. 	# For the nth letter of the plaintext, apply the nth key (modulo the key length)
  24. 	# And hence shift the number that many places
  25. 	$encnum = array();
  26. 	foreach($numbers as $pos => $num) {
  27. 		$shift = $key[$pos % count($key)];
  28. 		# Add the incerement times the position (starting at 1) 
  29. 		$shift += (($pos + 1) * $inc) % 26;
  30. 		$encnum[] = ($num + $shift) % 26;
  31. 	}
  32. 	# Turn the numbers back into letters
  33. 	$enc = array();
  34. 	foreach($encnum as $num) {
  35. 		$enc[] = chr($num + 65);
  36. 	}
  37.  
  38. 	return implode('', $enc);
  39. }
  40.  
  41. function decrypt($enc, $key, $inc) {
  42. 	# Turn encrypted text into an array
  43. 	$enc = str_split($enc);
  44. 	# Turn encrypted text into numbers, A=0, ...Z=25
  45. 	$encnum = array();
  46. 	foreach($enc as $letter) {
  47. 		$encnum[] = ord($letter) - 65;
  48. 	}
  49. 	# Apply the key in reverse:
  50. 	# For the nth letter of the plaintext, apply the nth key (modulo the key length)
  51. 	# And hence shift the number that many places in the negative direction
  52. 	$numbers = array();
  53. 	foreach($encnum as $pos => $num) {
  54. 		$shift = $key[$pos % count($key)];
  55. 		# Add the incerement times the position (starting at 1)
  56. 		$shift += (($pos + 1) * $inc) % 26;
  57. 		$numbers[] = (($num - $shift)+52) % 26;
  58. 	}
  59. 	# Turn the numbers back into letters
  60. 	$text = array();
  61. 	foreach($numbers as $num) {
  62. 		$text[] = chr($num + 65);
  63. 	}
  64.  
  65. 	return implode('', $text);
  66. }
Success #stdin #stdout 0.01s 20520KB
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https://ideone.com/67MD5E
language:
PHP (php 7.3.5)
created:
9 years ago
visibility:
public

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