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  1. import binascii
  2. from Crypto.Cipher import AES
  3. from Crypto.Util import Counter
  4. from Crypto import Random
  5.  
  6. # AES supports multiple key sizes: 16 (AES128), 24 (AES192), or 32 (AES256).
  7. key_bytes = 32
  8.  
  9. # Takes as input a 32-byte key and an arbitrary-length plaintext and returns a pair (iv, ciphertext). "iv" stands for initialization vector.
  10. def encrypt(key, plaintext):
  11.     assert len(key) == key_bytes
  12.  
  13.     # Choose a random, 16-byte IV.
  14.     iv = Random.new().read(AES.block_size)
  15.  
  16.     # Convert the IV to a Python integer.
  17.     iv_int = int(binascii.hexlify(iv), 16) 
  18.  
  19.     # Create a new Counter object with IV = iv_int.
  20.     ctr = Counter.new(AES.block_size * 8, initial_value=iv_int)
  21.  
  22.     # Create AES-CTR cipher.
  23.     aes = AES.new(key, AES.MODE_CTR, counter=ctr)
  24.  
  25.     # Encrypt and return IV and ciphertext.
  26.     ciphertext = aes.encrypt(plaintext.encode('utf-8'))
  27.     return (iv, ciphertext)
  28.  
  29. # Takes as input a 32-byte key, a 16-byte IV, and a ciphertext, and outputs the corresponding plaintext.
  30. def decrypt(key, iv, ciphertext):
  31.     assert len(key) == key_bytes
  32.  
  33.     # Initialize counter for decryption. iv should be the same as the output of encrypt().
  34.     iv_int = int(binascii.hexlify(iv), 16)
  35.     ctr = Counter.new(AES.block_size * 8, initial_value=iv_int)
  36.  
  37.     # Create AES-CTR cipher.
  38.     aes = AES.new(key, AES.MODE_CTR, counter=ctr)
  39.  
  40.     # Decrypt and return the plaintext.
  41.     plaintext = aes.decrypt(ciphertext)
  42.     return plaintext.decode('utf-8')
  43.  
  44. # Example usage
  45. key = '01234567890123456789012345678901'.encode('utf-8')
  46. (iv, ciphertext) = encrypt(key, 'Coronavirus')
  47. plaintext = decrypt(key, iv, ciphertext)
  48.  
  49. print("Ciphertext: {}".format(binascii.hexlify(ciphertext).decode('utf-8')))
  50. print("Decrypted plaintext: {}".format(plaintext))
Success #stdin #stdout 0.03s 11440KB
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Standard input is empty
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Ciphertext: 6fbcc5742d4438eb8711a4
Decrypted plaintext: Coronavirus
https://ideone.com/Q57vCX
language:
Python (cpython 2.7.16)
created:
2 days ago
visibility:
public

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