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  1. <?php
  2.  
  3. # Part I: Keyed Caesar
  4. # Example usage:
  5. # encrypt('Hello cipher world!',array(1,19,6,4));
  6. # decrypt('MMRIYUIYCPJLRCSLYQBRV',array(7,24,3));
  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) {
  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. 		$encnum[] = ($num + $shift) % 26;
  29. 	}
  30. 	# Turn the numbers back into letters
  31. 	$enc = array();
  32. 	foreach($encnum as $num) {
  33. 		$enc[] = chr($num + 65);
  34. 	}
  35.  
  36. 	return implode('', $enc);
  37. }
  38.  
  39. function decrypt($enc, $key) {
  40. 	# Turn encrypted text into an array
  41. 	$enc = str_split($enc);
  42. 	# Turn encrypted text into numbers, A=0, ...Z=25
  43. 	$encnum = array();
  44. 	foreach($enc as $letter) {
  45. 		$encnum[] = ord($letter) - 65;
  46. 	}
  47. 	# Apply the key in reverse:
  48. 	# For the nth letter of the plaintext, apply the nth key (modulo the key length)
  49. 	# And hence shift the number that many places in the negative direction
  50. 	$numbers = array();
  51. 	foreach($encnum as $pos => $num) {
  52. 		$shift = $key[$pos % count($key)];
  53. 		$numbers[] = (($num - $shift)+26) % 26;
  54. 	}
  55. 	# Turn the numbers back into letters
  56. 	$text = array();
  57. 	foreach($numbers as $num) {
  58. 		$text[] = chr($num + 65);
  59. 	}
  60.  
  61. 	return implode('', $text);
  62. }
Success #stdin #stdout 0.01s 20568KB
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https://ideone.com/HQGUaz
language:
PHP (php 7.3.5)
created:
9 years ago
visibility:
public

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