Public key cryptography (Asymmetric)

• Symmetric key cryptography is fast and efficient but it suffers from a disadvantage of problem of key exchange

• The sender and the receiver of an encrypted message use the same key in symmetric key cryptography and it is not easy to again upon a common key without letting anyone else know about it

• Asymmetric key cryptography solves this problem

• Here, the communicating party uses two keys to form a pair

$\hspace{1.5cm}$a. One key (the private key) remains with the party

$\hspace{1.5cm}$b. Other key (public key) is shared with everybody

Working of Asymmetric key cryptography:

• When A wants to send a message to B , A encrypts the message using B’s public key. This is possible because A knows B’s public key

• A sends this message (which was encrypted with B’s public key to B

• B decrypts A’s message using B’s private key. Every B knows his private key and the message can be decrypted only by B’s private key and nobody else. Thus no one else can make out any sense out of the message. This is because the intruder does not know about B’s private key. It is only B’s private key that can decrypt the message. Similarly, when B wants to send a message to A, exactly reverse steps take place. Ie B encrypts the message using A’s public key therefore, only A can decrypts the message back to its original forms, using his Private Key