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import sys import os import random from collections import defaultdict, Counter def main(): # Funció principal del script message = input("Enter plaintext or ciphertext: ") process = input("Enter 'encrypt' or 'decrypt': ") while process not in ('encrypt', 'decrypt'): process = input("Invalid process. Enter 'encrypt' or 'decrypt': ") shift = int(input("Shift value (1-366) = ")) while not 1 <= shift <= 366: shift = int(input("Invalid value. Enter digit from 1 to 366: ")) infile = input("Enter filename with extension: ") if not os.path.exists(infile): print("File {} not found. Terminating.".format(infile), file=sys.stderr) sys.exit(1) text = load_file(infile) char_dict = make_dict(text, shift) if process == 'encrypt': ciphertext = encrypt(message, char_dict) # Run QC protocols and print results. if check_for_fail(ciphertext): print("\nProblem finding unique keys.", file=sys.stderr) print("Try again, change message, or change code book.\n", file=sys.stderr) sys.exit() print("\nCharacter and number of occurrences in char_dict: \n") print("{: >10}{: >10}{: >10}".format('Character', 'Unicode', 'Count')) for key in sorted(char_dict.keys()): print('{:>10}{:>10}{:>10}'.format(repr(key)[1:-1], str(ord(key)), len(char_dict[key]))) print('\nNumber of distinct characters: {}'.format(len(char_dict))) print("Total number of characters: {:,}\n".format(len(text))) print("encrypted ciphertext = \n {}\n".format(ciphertext)) # Check the encryption by decrypting the ciphertext. print("decrypted plaintext = ") for i in ciphertext: print(text[i - shift], end='', flush=True) elif process == 'decrypt': plaintext = decrypt(message, text, shift) print("\ndecrypted plaintext = \n {}".format(plaintext)) def load_file(infile): """Read and return text file as a string of lowercase characters.""" with open(infile) as f: loaded_string = f.read().lower() return loaded_string def make_dict(text, shift): """Return dictionary of characters as keys and shifted indexes as values.""" char_dict = defaultdict(list) for index, char in enumerate(text): char_dict[char].append(index + shift) return char_dict def encrypt(message, char_dict): """Return list of indexes representing characters in a message.""" encrypted = [] for char in message.lower(): if len(char_dict[char]) > 1: index = random.choice(char_dict[char]) elif len(char_dict[char]) == 1: # Random.choice fails if only 1 choice. index = char_dict[char][0] elif len(char_dict[char]) == 0: print("\nCharacter {} not in dictionary.".format(char), file=sys.stderr) continue encrypted.append(index) return encrypted def decrypt(message, text, shift): """Decrypt ciphertext list and return plaintext string.""" plaintext = '' indexes = [s.replace(',', '').replace('[', '').replace(']', '') for s in message.split()] for i in indexes: plaintext += text[int(i) - shift] return plaintext def check_for_fail(ciphertext): """Return True if ciphertext contains any duplicate keys.""" check = [k for k, v in Counter(ciphertext).items() if v > 1] if len(check) > 0: return True if __name__ == '__main__': main()
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