PGP (Pretty Good Privacy) is one of the most widely used encryption systems in the world. Created in 1991 by Phil Zimmermann, it uses a combination of symmetric and asymmetric encryption to secure messages and files. Despite its age, the cryptographic principles behind PGP remain sound, and it is still the standard for encrypted email and file verification.
How PGP Works: The Key Pair
PGP uses two keys: a public key you share with everyone and a private key you keep secret. Anyone can encrypt a message using your public key, but only your private key can decrypt it. This solves the fundamental problem of key exchange — you never need to transmit your secret key to anyone.
Encryption and Signing
PGP provides two distinct functions: encryption (confidentiality) and signing (authenticity). Encryption ensures only the intended recipient can read a message. Signing proves that a message came from you and has not been altered. You can use either function independently or combine them for maximum security.
The Web of Trust
Unlike certificate authorities used in HTTPS, PGP uses a decentralized "web of trust" model. Users verify each other’s identities and sign each other’s public keys. If you trust Alice and Alice has verified Bob’s key, you can trust Bob’s key transitively. This model does not require a central authority, making it resistant to single points of failure.
Practical Challenges
PGP’s biggest challenge is usability. Key management, key servers, trust verification, and the command-line tools can be intimidating for beginners. The learning curve is steeper than most modern messaging apps, which handle encryption transparently. This complexity has limited PGP’s adoption despite its strong security properties.
Getting Started
Start by generating a key pair using GPG (GNU Privacy Guard), the open-source implementation of PGP. Share your public key with people you want to communicate with securely. Use a passphrase to protect your private key — if someone obtains your private key file, the passphrase is your last line of defense.
PGP on Mobile
LockWhisper for iOS includes PGP encryption support, making it easy to encrypt and decrypt messages on your iPhone. The app handles key management and encryption operations locally, so your private key never leaves your device. This brings PGP’s strong encryption to mobile without the complexity of command-line tools.