GnuPG is a tool for secure communication. This chapter is a quick-start guide that covers the core functionality of GnuPG. This includes keypair creation, exchanging and verifying keys, encrypting and decrypting documents, and authenticating documents with digital signatures. It does not explain in detail the concepts behind public-key cryptography, encryption, and digital signatures. This is covered in Chapter 2. It also does not explain how to use GnuPG wisely. This is covered in Chapters 3 and 4.

GnuPG uses public-key cryptography so that users may communicate securely. In a public-key system, each user has a pair of keys consisting of a private key and a public key. A user's private key is kept secret; it need never be revealed. The public key may be given to anyone with whom the user wants to communicate. GnuPG uses a somewhat more sophisticated scheme in which a user has a primary keypair and then zero or more additional subordinate keypairs. The primary and subordinate keypairs are bundled to facilitate key management and the bundle can often be considered simply as one keypair.