The key itself was encrypted but the English frequently intercepted and decrypted it and therefore decrypt all of the German messages sent that day. The German were unaware that their message were being read, and this fact proved particularly damaging to them

In 1976, Diffie and Hellman proposed a solution. They suggested that two keys be used. The first key would be used for encryption and would be PUBLIC - that is, it could be known to anyone intercepting would still be unable to decrypt the message.