Public key / Private key encryption using polkadot lib?

Question

I'm building a substrate blockchain backed by polkadot js. While working on a task I have a requirement of public/private key encryption and decryption. for ex: Bob wants to send Alice an encrypted email. To do this, Bob takes Alice's public key and encrypts his message to her. Then, when Alice receives the message, she takes the private key that is known only to her in order to decrypt the message from Bob. Does anyone know how this is done through Polkadot js library? Help will be appreciated!