In order to send an encrypted message, you need a public encryption key paired with a private key. A good option for this is PGP. To get setup quickly and easily, you can use the GPG Suite to generate your PGP key, as well as giving you great OS-level encryption/decryption support on the GIU, and the terminal.
- Download and Install GPG Suite: (not the Beta) https://gpgtools.org/
- Open GPG Keychain
- Click "New" to create a new PGP key
- Use your doodle email address and full name