Lecture 8 : Public - Key Encryption

In the previous lecture, we discussed the concept of Secret-Key Encryption. However, this scheme has a major limitation in the fact that the key has to be shared between the sender and the receiver before any message can be transmitted. There might be several cases where doing this is infeasible if there has been no prior communication between the sender and the receiver. In today’s lecture, we will look at an encryption scheme which provides a solution for this problem. This encryption scheme is called Public-Key Encryption. In this scheme, instead of a single shared secret key, the sender and the receiver now each have two keys a public key and a secret key. The public key can be made public without giving away any information that can reduce the overall security of the scheme. The secret key remains secret, just like in Secret-Key Encryption. When a sender wants to send a message to the receiver, she uses the public key of the receiver to encrypt it. The receiver then uses his secret key to decrypt the message. There is no secret shared between the sender and the receiver in this scheme.