import sys import string d={} for i in range(26): d[chr(i+97)]=i e={} for i in range(26): e[i]=chr(i+97) plain_text=raw_input("enter plain text") key=input("enter key") cipher_text=[None]*len(plain_text) l=list(plain_text) cipher_list=[None]*len(plain_text) for i in range(len(plain_text)): cipher_list[i]=e[((d[l[i]]+key)%26)] print string.join(cipher_list, '')