Fundamentals of Cryptography

Message Privacy Using a Public Key

One problem in the previous example is that Alice’s message is readable by everyone. There is no notion of privacy. Privacy can be achieved using the inverse of the previous methods. If Alice were to send a message, such that the message was only readable by Bob, then Alice would perform the following operation.


At this point the only way to decrypt this information is to use Bob’s private key, which only Bob has. Again, the only verification that is assured by public key cryptography is that the owner of Bob’s private key is the only entity capable of decrypting this message. If Bob’s private key is not sufficiently protected by his key management system, then we cannot be assured that Bob is the only person who can read the message. Assuming that Bob has access to his private key, he performs the following operation.


Bob is now able to read the message.