Noise Protocol
Cryptographic protocol framework from Trevor Perrin (also Signal Protocol co-author), 2016. Builds handshakes from DH + cipher + hash primitives via "patterns" (IK, XX, NK etc). Powers WireGuard + WhatsApp + Lightning Network.
Distinct from TLS: simpler, less flexibility, formally verified. Noise has 10+ standardized patterns for different trust models: IK (initiator knows responder's static pubkey), XX (mutual auth), NK (anonymous initiator, known responder). WireGuard uses modified Noise IK. Implementation-wise: noise-c (C reference), noise-protocol-rust, snow (Rust), tor's pq-noise (post-quantum). Modern crypto design prefers Noise over custom handshakes — fewer footguns.