If you were writing to me concerning a problem with your medical treatment, you would probably prefer that only I could read your message. You publish your public key to the world while keeping your private key secret. For a clear and fairly concise detailed explanation, please click here . PGP comes with plug-ins to seamlessly integrate it into all of the common mail programs. PGP is free for personal use, since it was developed with public funds.
Commercial versions are available at most software retailers.