PGP = Pretty Good Privacy. It’s both a company and the original product released by Phil Zimmerman that has since been mostly replaced by Gnu Privacy Guard (GPG).

These products create paired secret keys using the ciphers of your choice. You make the public key available to the public and keep the private key for yourself.

Then, you can either sign or encrypt some content with your private key, and anyone with your public key can validate that it was you who signed or encrypted the file.

You can also use someone else’s public key to encrypt a file, and then only the holder of the paired private key can decrypt it. And they can use your public key to validate that it was you who encrypted it.

Email addresses are optional, but can be embedded in the keypair. This means that someone else can verify that that address is linked with the identity of that keyholder, which assists in getting encrypted content to the right recipient, validates any signed/encrypted email sent from that address, and provides a memorable link to the public key’s owner.