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  1. # Part II: Hardened Keyed Caesar
  2. # Example usage:
  3. # encrypt('Ciphers are hard!',[1,2,3,4],3);
  4. # decrypt('GQBXULQCTKROFV',[1,2,3,4],3);
  5. # Note the these functions are not strictly inverses of each other,
  6. # as the decryption function does not restore spaces or punctuation.
  7.  
  8. import re
  9.  
  10. def encrypt(text, key, inc):
  11. 	# Turn text to uppercase
  12. 	text = text.upper()
  13. 	# Remove spaces and punctuation
  14. 	text = re.sub(r'[^A-Z]','',text)
  15. 	# Turn text into numbers, A=0, ...Z=25
  16. 	numbers = []
  17. 	for letter in text:
  18. 		numbers.append(ord(letter) - 65)
  19. 	# Apply the key:
  20. 	# For the nth letter of the plaintext, apply the nth key (modulo the key length)
  21. 	# And hence shift the number that many places
  22. 	encnum = []
  23. 	for (pos, num) in enumerate(numbers):
  24. 		shift = key[pos % len(key)]
  25. 		# Add the incerement times the position (starting at 1)
  26. 		shift += ((pos + 1) * inc) % 26
  27. 		encnum.append((num + shift) % 26)
  28. 	# Turn the numbers back into letters
  29. 	enc = []
  30. 	for num in encnum:
  31. 		enc.append(chr(num + 65))
  32.  
  33. 	return ''.join(enc)
  34.  
  35. def decrypt(enc, key, inc):
  36. 	# Turn encrypted text into numbers, A=0, ...Z=25
  37. 	encnum = []
  38. 	for letter in enc:
  39. 		encnum.append(ord(letter) - 65)
  40. 	# Apply the key in reverse:
  41. 	# For the nth letter of the plaintext, apply the nth key (modulo the key length)
  42. 	# And hence shift the number that many places in the negative direction
  43. 	numbers = []
  44. 	for (pos, num) in enumerate(encnum):
  45. 		shift = key[pos % len(key)]
  46. 		# Add the incerement times the position (starting at 1)
  47. 		shift += ((pos + 1) * inc) % 26
  48. 		numbers.append((num - shift + 52) % 26)
  49. 	# Turn the numbers back into letters
  50. 	text = []
  51. 	for num in numbers:
  52. 		text.append(chr(num + 65))
  53.  
  54. 	return ''.join(text)
Success #stdin #stdout 0.09s 10088KB
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https://ideone.com/rtv6gY
language:
Python 3 (python  3.9.5)
created:
9 years ago
visibility:
public

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