Python ARC4 String Encryption & Decryption

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#==============MODULES================#
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from Crypto.Cipher import *
from Crypto import Random
import base64

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#==============VARIABLES==============#
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mtypes = ["(1) Encrypt", "(2) Decrypt", "(3) Exit   "]
block_size = 8
key_size = 8

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#==============FUNCTIONS==============#
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#create menu
def menu(parameter):
    print "         +===========+"
    print "         |    MENU   |"
    print "         |-----------|"
    for word in parameter:
        print "         |%s|" % word
        print "         |-----------|"

#defines encryption algorithm
def enc(key_size, block_size):

    #get key and pad if necessary
    key = raw_input("Please enter a key: ")
    key += (key_size - len(key) % key_size) * chr(key_size - len(key) % key_size)

    #get data and pad if necessary
    data = raw_input("Please enter a string to encrypt: ")
    pad = lambda data: data + (block_size - len(data) % block_size) * chr(block_size - len(data) % block_size)
    data = pad(data)

    #define what is needed for DES
    cipher = ARC4.new(key)

    #combine IV and encrypted text | encode using base64
    output = base64.b64encode(iv + cipher.encrypt(data))

#defines decryption algorithm
def dec(key_size, block_size):

    #get key and pad if necessary
    key = raw_input("Please enter a key: ")
    key += (key_size - len(key) % key_size) * chr(key_size - len(key) % key_size)

    #get data and decode base64
    data = raw_input("Please enter a string to decrypt: ")
    data = base64.b64decode(data)

    #strip padding
    strippad = lambda data: data[0:-ord(data[-1])]

    #define what is needed for DES
    cipher = ARC4.new(key)

    #strip off padding and decrypt data
    output = strippad(cipher.decrypt(data))

    print "The decrypted message is: ", output

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#===========MAIN PROGRAM==============#
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def main():
    menu(mtypes)
    mtypes_choice = input("Please select to encrypt, decrypt, or exit(1-3): ")

    #Encryption
    if mtypes_choice == 1:
        enc(key_size, block_size)

    #Decryption
    elif mtypes_choice == 2:
        dec(key_size, block_size)

    #Exit
    elif mtypes_choice == 3:
        print "Exiting Program. Goodbye."
        print
        return

    #Fault
    else:
        print "ERROR. Invalid Selection."
        print
        print
        return main()