2021-csci-ga3205-midterm/index.py

import argparse


def caesar(p_text_letter, key_letter):
    p_text_num = ord(p_text_letter) - ord('A')
    key_letter_num = ord(key_letter) - ord('A')
    return chr((p_text_num + key_letter_num) % 26 + ord('A'))


def caesar_reverse(c_text_letter, key_letter):
    c_text_num = ord(c_text_letter) - ord('A')
    key_letter_num = ord(key_letter) - ord('A')
    return chr((c_text_num - key_letter_num) % 26 + ord('A'))


def encryption(plaintext, key):
    ciphertext = ''
    for i in range(len(plaintext)):
        ciphertext += caesar(plaintext[i], key[i % len(key)])
    return ciphertext


def decryption(ciphertext, key):
    plaintext = ''
    for i in range(len(ciphertext)):
        plaintext += caesar_reverse(ciphertext[i], key[i % len(key)])
    return plaintext.lower()


def main():
    parser = argparse.ArgumentParser()
    parser.add_argument('--text', type=str)
    parser.add_argument('--key', type=str)
    args = parser.parse_args()

    print("Encrypted ciphertext: " + encryption(args.text.upper().replace(" ", ""), args.key))
    print("Decrypted plaintext: " + decryption(args.text.lower().replace(" ", ""), args.key))


if __name__ == '__main__':
    main()