- Generate RSA keypairs locally
- Import others' public keys and encrypt messages to send to others
- Decrypt messages others sent to you with your private key
- Sign / Verify message signature

Best of all, encryption and decryption of messages can be done directly in the iMessage app. When using the in-app extension, you no longer have to send a long piece of string, the encrypted message is embedded into an iMessage object so the other side can just click and decrypt.