Python DES String Encryption & Decryption

#=====================================#
#==============MODULES================#
#=====================================#

from Crypto.Cipher import *
from Crypto import Random
import base64

#=====================================#
#==============VARIABLES==============#
#=====================================#

modes = ["(1) ECB    ", "(2) CBC    ", "(3) CFB    "]
mtypes = ["(1) Encrypt", "(2) Decrypt", "(3) Exit   "]
block_size = 8
key_size = 8
iv_size = 8

#=====================================#
#==============FUNCTIONS==============#
#=====================================#

#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, iv_size, mode):

    #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)

    #generate random IV
    iv = Random.new().read(iv_size)

    #define what is needed for DES
    cipher = DES.new(key, mode, iv)

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

def dec(key_size, block_size, iv_size, mode):

    #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)

    #get IV
    iv = data[:iv_size]

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

    #define what is needed for DES
    cipher = DES.new(key, mode, iv)

    #strip off padding and decrypt data
    output = strippad(cipher.decrypt(data[iv_size:]))

    print "The decrypted message is: ", output

#=====================================#
#===========MAIN PROGRAM==============#
#=====================================#

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

    #Encryption
    if mtypes_choice == 1:
        menu(modes)
        menus_choice = input("Please select a mode of encryption(1-3): ")

        if menus_choice == 1:
            mode = DES.MODE_ECB
            enc(key_size, iv_size, block_size, mode)
        elif menus_choice == 2:
            mode = DES.MODE_CBC
            enc(key_size, iv_size, block_size, mode)
        elif menus_choice == 3:
            mode = DES.MODE_CFB
            enc(key_size, iv_size, block_size, mode)

    #Decryption
    elif mtypes_choice == 2:
        menu(modes)
        menus_choice = input("Please select a mode of encryption(1-3): ")

        if menus_choice == 1:
            mode = DES.MODE_ECB
            dec(key_size, iv_size, block_size, mode)
        elif menus_choice == 2:
            mode = DES.MODE_CBC
            dec(key_size, iv_size, block_size, mode)
        elif menus_choice == 3:
            mode = DES.MODE_CFB
            dec(key_size, iv_size, block_size, mode)

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

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