How VPN Encryption Works

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What encryption is

Encryption transforms readable data into scrambled ciphertext readable only by someone with the correct decryption key. Only your device and the VPN server hold the key.

AES-256 — the standard

AES-256-GCM is used by virtually every quality VPN. Breaking it by brute force would require more energy than exists in the observable universe. It is the same standard used by governments, banks, and militaries worldwide.

The handshake

Before encrypting your session, your device and the server agree on keys using asymmetric encryption — RSA-4096 or elliptic curve Diffie-Hellman. The public key encrypts; the private key decrypts. The session then switches to symmetric AES-256 for speed.

Perfect Forward Secrecy

A new encryption key is generated for every session. Even if a past key were somehow compromised, earlier and later sessions remain fully protected. Each session is mathematically independent.

WireGuard's approach

WireGuard uses ChaCha20-Poly1305 instead of AES. On devices without hardware AES acceleration, ChaCha20 runs faster in pure software while providing equivalent security. It also uses Curve25519 for key exchange and BLAKE2s for hashing — all modern, well-audited algorithms.

Post-quantum encryption

ExpressVPN has added ML-KEM post-quantum key exchange to its WireGuard implementation. NordVPN and ProtonVPN are also integrating post-quantum cryptography to protect against future quantum computer decryption attacks.