vernam_cipher.py

defvernam_encrypt(plaintext: str, key: str) ->str:
"""
 >>> vernam_encrypt("HELLO","KEY")
 'RIJVS'
 """
ciphertext=""
foriinrange(len(plaintext)):
ct=ord(key[i%len(key)]) -65+ord(plaintext[i]) -65
whilect>25:
ct=ct-26
ciphertext+=chr(65+ct)
returnciphertext


defvernam_decrypt(ciphertext: str, key: str) ->str:
"""
 >>> vernam_decrypt("RIJVS","KEY")
 'HELLO'
 """
decrypted_text=""
foriinrange(len(ciphertext)):
ct=ord(ciphertext[i]) -ord(key[i%len(key)])
whilect<0:
ct=26+ct
decrypted_text+=chr(65+ct)
returndecrypted_text


if__name__=="__main__":
fromdoctestimporttestmod

testmod()

# Example usage
plaintext="HELLO"
key="KEY"
encrypted_text=vernam_encrypt(plaintext, key)
decrypted_text=vernam_decrypt(encrypted_text, key)
print("\n\n")
print("Plaintext:", plaintext)
print("Encrypted:", encrypted_text)
print("Decrypted:", decrypted_text)