Noise Protocol: A Minimal and Modular Cryptographic Tool
Been working with the Noise protocol recently — here’s a quick breakdown of what it does and how it works under the hood.
Noise is a small framework for building secure handshakes. It’s not a full protocol like TLS, more like a toolkit to define your own. It handles the initial key exchange, identity/auth, and gives you encrypted transport keys after the handshake. That’s it. No certificates, no extensions, no middleboxes.
Each handshake in Noise is built using a "pattern" — I’ve been using XX and NX. These define how the keys are exchanged:
* XX: both sides are anonymous, and exchange keys during handshake.
* NX: responder has a static pubkey, initiator is ephemeral (closer to client-server flows like SV2).
Behind the scenes, these patterns are just sequences of Diffie-Hellman operations between the parties' keys (ephemeral and static), and the handshake hash is updated after each message. Once complete, both sides split the final hash into two symmetric cipherstates, and that’s what’s used to encrypt transport messages.
All operations are constant-time. I’m using the `noise-c` library, which supports `Noise_XX_25519_ChaChaPoly_BLAKE2s` (or SHA256 if you tweak the suite string). Noise defines the handshake state machine, but the crypto primitives are pluggable.
The nice part is that everything’s deterministic and testable. Given the same inputs, the handshake always produces the same shared keys. It’s all pure key material — no ASN.1, no PEMs, no handshake extensions to worry about.
In the next post, I’ll show a tiny C implementation that wraps a Noise handshake (XX or NX), and exchanges Stratum V2 `SetupConnection` messages post-handshake. Useful for testing your own SV2 client/server implementations.
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