Crypto Interface — NTL Specification

Version: beta_0.0.0

Overview

NTL defines a cryptographic module interface that all signing, verification, encryption, and key exchange operations MUST go through. No cryptographic algorithm is hardcoded into the protocol.

Interface

Implementations MUST provide a module that satisfies this interface:

CryptoModule {
    // Identity
    module_id() -> string

    // Key management
    generate_keypair() -> (PublicKey, PrivateKey)

    // Signing
    sign(data: bytes, key: PrivateKey) -> Signature
    verify(data: bytes, signature: Signature, key: PublicKey) -> bool

    // Encryption
    encrypt(data: bytes, recipient_key: PublicKey) -> bytes
    decrypt(data: bytes, key: PrivateKey) -> bytes

    // Key exchange
    key_exchange(local: PrivateKey, remote: PublicKey) -> SharedSecret

    // Hashing
    hash(data: bytes) -> Hash
}

Module Negotiation

During synapse handshake, nodes exchange their supported crypto module IDs. The synapse MUST use a mutually supported module. If no common module exists, the synapse formation MUST fail. Priority order for module selection:

Both nodes’ preferred module (if same)
Highest-versioned mutually supported module
Failure (no common module)

Modules

Module ID	Algorithms	Status	In the reference implementation
`classical-v1`	Ed25519 + X25519 + AES-256-GCM + BLAKE3	REQUIRED	Yes — signing and verification
`pq-v1`	Dilithium + Kyber + AES-256-GCM + BLAKE3	RECOMMENDED	No
`hybrid-v1`	Both PQ and classical (dual signatures)	OPTIONAL	No

An implementation MUST provide classical-v1 — it is the floor that makes two arbitrary nodes able to negotiate anything at all.

pq-v1 is specified but not implemented in the reference implementation, and 0.1.0-draft was wrong to call it the default. A node whose configuration names an unimplemented module MUST fail to start with an error naming the modules it does support. It MUST NOT fall back to a different module silently: an operator who asked for post-quantum signing and got Ed25519 has been told the opposite of the truth about their deployment’s confidentiality horizon.The reference implementation enforces this in NodeConfig::validate, and crypto::supported_modules() is the single list it checks against.

The point of this interface is that the choice is not baked into the protocol — not that any particular module already exists. Post-quantum readiness means a node can adopt pq-v1 without a wire-format change, which holds today.

Key Serialization

Public keys MUST be serializable to bytes for inclusion in signal origin fields and synapse handshakes. The serialization format is module-specific but MUST be deterministic.

Module Registration

Implementations MUST support runtime registration of custom crypto modules:

register_module(module: CryptoModule) -> Result
set_default_module(module_id: string) -> Result
list_modules() -> [ModuleInfo]

​Overview

​Interface

​Module Negotiation

​Modules

​Key Serialization

​Module Registration