Public Key Cryptography uses two keys, a Public key and a Private key. PGP Uses the RSA Cryptosystem. The basic premise: Using one key to encrypt requires the other key to decrypt:

- Private Key
- User keeps secret -- no one should see this key
- Encryption creates Digital Signature
- Decryption opens sealed messages

- Public Key
- User makes public -- anyone can see this key
- Encryption seals messages
- Decryption verifies Digital Signature

- Users can distribute Public Keys to anyone
- Knowing the Public Key does not help an attacker find the Private Key
- Has Digital Signatures