WireGuard.

WireGuard, created by Jason Donenfeld, is a VPN designed for simplicity and performance, with a codebase orders of magnitude smaller (~4,000 lines) than IPsec or OpenVPN — a small attack surface that makes it far easier to audit. It uses a fixed, non-negotiable cryptographic suite (Curve25519 for key exchange, ChaCha20-Poly1305 for authenticated encryption per RFC 8439, BLAKE2s for hashing, HKDF, and the Noise IK 1-RTT handshake), eliminating the cipher-downgrade and negotiation-complexity flaws that have plagued IPsec/IKE and TLS. Peers are identified by static public keys through a model Donenfeld calls "cryptokey routing," and the handshake provides perfect forward secrecy by rotating ephemeral keys.

The protocol's security was formally verified: Donenfeld and Kevin Milner modeled the handshake in the Tamarin prover, and later work produced a mechanized computational proof in CryptoVerif. WireGuard was mainlined into the Linux kernel in version 5.6 (2020), with userspace and wireguard-go ports for other systems. Running over UDP/51820, it stays silent to unsolicited packets, survives IP roaming seamlessly, and underpins mesh overlays such as Tailscale and Netmaker. A design trade-off is that WireGuard keeps peer state and last-known endpoints, so operators layer it with dynamic address management for large fleets.

flowchart LR
  A[Peer A<br/>static public key] -->|Noise IK handshake<br/>1-RTT over UDP/51820| B[Peer B<br/>static public key]
  B -->|Ephemeral keys derived| C[Curve25519 shared secret]
  C --> D[ChaCha20-Poly1305<br/>encrypted tunnel]
  D --> E{Cryptokey routing}
  E -->|AllowedIPs match| F[Deliver to peer]
  E -->|No match| G[Drop packet]