Python XOR String Encryption & Decryption

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#==============MODULES================#
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from Crypto.Cipher import XOR
import base64

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

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#==============FUNCTIONS==============#
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#creates 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 data if necessary
    data = raw_input("Please enter a string: ")
    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 XOR
    cipher = XOR.new(key)

    #encode using base64 and encrypt data
    output = base64.b64encode(cipher.encrypt(data))

    print "The encrypted message is: ", output

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 using base64
    data = raw_input("Please enter a string: ")
    data = base64.b64decode(data)

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

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

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

    print "The decrypted message is: ", output

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#===========MAIN PROGRAM==============#
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def main():
    menu(menus)
    choice = input("Please make a selection(1-3): ")

    #Encryption
    if choice == 1:
        enc(key_size, block_size)
    #Decryption
    elif choice == 2:
        dec(key_size, block_size)
    #Exit
    elif choice == 3:
        print "Exiting Program. Goodbye!"
        print
        print
        return
    #Invalid Choice
    else:
        print "ERROR. Invalid Selection. "
        print
        print
        return main()