VigenereCipher.py

#!/usr/bin/env python2.7

"""Vigenere Cipher"""

from string import ascii_uppercase as alphabet

__author__ = 'Palmer (pzp1997)'
__version__ = '1.0.0'
__email__ = '[email protected]'

val = {}
for x in xrange(len(alphabet)):
    val[alphabet[x]] = x
    val[x] = alphabet[x]

encrypt = lambda a, b: ''.join(val[(val[a[i]]+val[b[i%len(b)]])%26] for i in xrange(len(a)))
decrypt = lambda a, b: ''.join(val[(val[a[i]]-val[b[i%len(b)]])%26] for i in xrange(len(a)))


def main():
    i = ''
    while i.lower() not in ['encrypt', 'decrypt']:
        i = raw_input("ENCRYPT or DECRYPT: ")

    message = raw_input("Plaintext: ") if i == 'encrypt' else raw_input("Ciphertext: ")
    message = filter(str.isupper, message.upper())
    key = filter(str.isupper, raw_input("Key: ").upper())

    print encrypt(message, key) if i == 'encrypt' else decrypt(message, key)

if __name__ == '__main__':
    main()