#!/usr/bin/python

# Uses Python2, need to edit print statements for python3 compatibility

# usage:

# python vigenere.py <-e,-d> <keyword> <message>

import sys

keyword = "A"

message = ["Hello","World"]

flag = 1

if(len(sys.argv) == 1):

print("What do you want to do ?\n1) Encrypt \n2) Decrypt")

i = input()

if(i<=0 or i>2):

print("Invalid option")

exit()

flag =i

print("Enter Keyword: ")

keyword = raw_input()

if(keyword.isalpha()==False):

print("Only alphabets allowed. No spaces.")

exit()

print("Enter message: ")

message = raw_input().split(' ')

for t in message:

if(t.isalpha()==False):

print("Only alphabets allowed in message.")

exit()

elif (len(sys.argv) >= 3):

trigger = sys.argv[1]

if(trigger == "-e"):

flag = 1

elif(trigger == "-d"):

flag = 2

else:

print("Invalid Flag.")

keyword = sys.argv[2]

message = sys.argv[3:]

if(keyword.isalpha()==False):

print("Usage: python vignere.py -e <KeyWord> <Message>.\nOnly alphabets allowed in Keyword.\n-e to encrypt, -d to decrypt")

exit()

for t in message:

if(t.isalpha()==False):

print("Usage: python vignere.py <KeyWord> <Message>.\nOnly alphabets allowed in message.\n-e to encrypt, -d to decrypt")

exit()

else:

print("Usage: python vignere.py <KeyWord> <Message>.\nOnly alphabets allowed in both keyword and message.\nNo spaces in the keyword allowed.\n-e to encrypt, -d to decrypt")

j = 0

def encrypt(key, mess):

global j

key = key.lower()

res = ""

mess = mess.lower()

for i in range(0,len(mess)):

shiftamt = ord(key[j]) - ord('a')

x = ord(mess[i]) + shiftamt

while (x > ord('z')):

x -= (ord('z')-ord('a'))

while (x < ord('a')):

x += (ord('z')-ord('a'))

res = res + chr(x)

j = (j+1)%(len(key))

return res

def decrypt(key, mess):

global j

key = key.lower()

res = ""

mess = mess.lower()

for i in range(0,len(mess)):

shiftamt = ord(key[j]) - ord('a')

x = ord(mess[i]) - shiftamt

while (x > ord('z')):

x -= (ord('z')-ord('a'))

while (x < ord('a')):

x += (ord('z')-ord('a'))

res = res + chr(x)

j = (j+1)%(len(key))

return res

# Instructions to use : Can be used both, interactively as well as via command line arguments

# Via command line parameters:

# Use for encryption : python vignere.py -e lemon attack at dawn

# Use for decryption : python vignere.py -d lemon lxgopv eg rnir

# Interactively just follow the prompts

if(flag == 1):

for i in range(0,len(message)):

print encrypt(keyword, message[i]),

elif(flag ==2):

for i in range(0,len(message)):

print decrypt(keyword, message[i]),