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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), 
  7. # or 32 (AES256).
  8. key_bytes = 32
  9. # You need to define 32-byte key. Like
  10. #     Key = '01234567890123456789012345678901'
  11. # Please refer this page on how to create key.
  12.  
  13. # Otherwise you will get this error.
  14.  
  15. # Takes as input a 32-byte key and an arbitrary-length 
  16. # plaintext and returns a pair (iv, ciphtertext). "iv" stands for 
  17. # initialization vector.
  18. def encrypt(key, plaintext):
  19.     assert len(key) == key_bytes
  20.  
  21.     # Choose a random, 16-byte IV.
  22.     iv = Random.new().read(AES.block_size)
  23.  
  24.     # Convert the IV to a Python integer.
  25.     iv_int = int(binascii.hexlify(iv), 16) 
  26.  
  27.     # Create a new Counter object with IV = iv_int.
  28.     ctr = Counter.new(AES.block_size * 8, initial_value=iv_int)
  29.  
  30.     # Create AES-CTR cipher.
  31.     aes = AES.new(key, AES.MODE_CTR, counter=ctr)
  32.  
  33.     # Encrypt and return IV and ciphertext.
  34.     ciphertext = aes.encrypt(plaintext)
  35.     return (iv, ciphertext)
  36.  
  37. # Takes as input a 32-byte key, a 16-byte IV, and a ciphertext, 
  38. # and outputs the corresponding plaintext.
  39. def decrypt(key, iv, ciphertext):
  40.     assert len(key) == key_bytes
  41.  
  42.     # Initialize counter for decryption. iv should be 
  43.     # the same as the output of encrypt().
  44.     iv_int = int(iv.encode('hex'), 16) 
  45.     ctr = Counter.new(AES.block_size * 8, initial_value=iv_int)
  46.  
  47.     # Create AES-CTR cipher.
  48.     aes = AES.new(key, AES.MODE_CTR, counter=ctr)
  49.  
  50.     # Decrypt and return the plaintext.
  51.     plaintext = aes.decrypt(ciphertext)
  52.     return plaintext
  53.  
  54. key = '01234567890123456789012345678901'
  55. (iv, ciphertext) = encrypt(key, 'Coronavirus')
  56. print (decrypt(key, iv, ciphertext))
Success #stdin #stdout 0.02s 11428KB
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Standard input is empty
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Coronavirus
https://ideone.com/MEYYS5
language:
Python (cpython 2.7.16)
created:
8 hours ago
visibility:
public

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