Auto Key Cipher

It is a very simple poly alphabetic cipher. In this cipher previous character of plain text used as key for encryption of next character using shift ( Caesar )cipher. And  for encryption of first character of plain text we use predetermine value secretly agreed upon by both communicator.

Python Sorce code :

1. 1. __auther__='Codecops.in'
   2. __email__='query.b2cs@gmail.com'
   4. #Auto Key Cipher
   5. def AutoKeyCipher(plainText,key):
   6.     #Auto Key Cipher
   7.     #only for Cpital letter
   8.     plainText=plainText.upper()
   9.     plainText=plainText.replace(' ','')
   10.     cipher=[]
   11.     #special case for 1st char
   12.     #print key
   13.     key=int(key)%26
   14.     cipher.append(chr(((ord(plainText[0])-65)+key)%26 +65))
   15.     for i in range(1,len(plainText)):
   16.         key=ord(plainText[i-1])-ord('A')
   17.         cipher.append(chr((((ord(plainText[i])-65)+key)%26 +65)))
   18.     return "".join(cipher)
   19. if __name__=="__main__":
   20.     #plT=raw_input("plainText : ")
   21.     plT='Attack is today'
   22.     key=raw_input("Key (int): ")
   23.     print AutoKeyCipher(plT,key)
   25. # http://codecops.in

GET More Basic Crypto Algorithms: Github