GnuPG
Official documentation
Generate a GPG key
gpg --full-generate-key
gpg --gen-key
Generate a revocation certificate
gpg --gen-revoke --output revoke.asc <user ID>
Ways to specify a user ID
List all keys
gpg --list-secret-keys
gpg --list-key
gpg -k
gpg --list-secret-keys --keyid-format=long
Export a public key
gpg --armor --export <user ID>
gpg --output username.gpg --export <user ID>
Import a public key
gpg --import alice.gpg
Export a fingerprint
gpg --fingerprint <user ID>
Encrypt a document
gpg --output doc.gpg --encrypt --recipient <recipient_email> doc
Decrypt a document
gpg --output doc --decrypt doc.gpg