Docs — Middn

01 ↘

Architecture overview

Middn is a P2P trading protocol built on three pillars: smart contracts that hold the funds, zero-knowledge proofs that verify conditions privately, and an AI agent that guides users through the flow. Every component is non-custodial and verifiable on-chain.

The flow at 10,000 feet

A Middn trade goes through 4 phases — each enforced by code, not by a backend service. There is no Middn server holding state in between.

→ how a trade flows

↳ what makes it different

Unlike a CEX, Middn has no order book, no matching engine, no custody layer. It's a protocol, not an exchange — closer to how Uniswap relates to Coinbase.

02 ↘

Smart contracts

The core of Middn is a set of atomic swap contracts built on HTLC primitives. Each trade deploys a new escrow instance (or registers in a singleton factory, depending on chain). Once deployed, the contract is immutable — neither we nor anyone else can modify it.

The escrow contract

A simplified version of the escrow logic:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

contract MiddnEscrow {
    address public buyer;
    address public seller;
    uint256 public amount;
    bytes32 public conditionHash;

    function release(bytes calldata zkProof) external {
        require(verify(zkProof, conditionHash), "invalid proof");
        // atomic settlement — both legs release together
        payable(seller).transfer(amount);
        emit Settled(buyer, seller, amount);
    }
}

Key properties

Immutable — once deployed, the contract logic cannot be changed. No admin keys, no proxy upgrades.
Atomic — settlement is all-or-nothing. Both transfers happen in the same transaction or neither does.
Refundable — if conditions aren't met before the timeout, both sides can withdraw their deposits.
Self-contained — no oracle dependency for settlement. The proof itself is sufficient.

03 ↘

Zero-knowledge proofs

Middn uses Groth16 zk-SNARKs to let users prove trade conditions are valid without revealing the underlying data. Amounts, identities, balances, conditions — everything stays private. The chain only sees a 192-byte proof.

→ zk verification flow

Circuits we use

conditionCheck — proves all trade conditions are satisfied without revealing them.
balanceProof — proves a user has sufficient balance without exposing the amount.
complianceProof — proves KYC status (when applicable) without leaking documents.

↳ why Groth16

We chose Groth16 over PLONK/Halo2 for verification cost: ~280k gas per proof on Ethereum mainnet. Setup is per-circuit, but circuits are public and reproducible.

04 ↘

End-to-end encryption

Trade invitations and counterparty messages are encrypted client-side. Middn's backend never sees plaintext. Even if our servers were compromised, attackers would only find ciphertext.

The cryptography stack

Component	Algorithm	Purpose
symmetric	AES-256-GCM	Payload encryption
key exchange	X25519 ECDH	Shared secret derivation
signing	Ed25519	Message authentication
kdf	HKDF-SHA256	Key derivation
hashing	BLAKE3	Content addressing

Each trade invitation generates a fresh ephemeral key pair. The shared secret is derived via X25519, and AES-256-GCM encrypts the payload. Forward secrecy means past trades stay private even if your wallet is later compromised.

05 ↘

Non-custodial by design

The most important property of Middn is what we don't do: we never hold user funds. Not for a millisecond. Not in a hot wallet. Not in cold storage. Never.

How it's enforced

No admin functions on contracts. No "pause" button, no "rescue" function, no upgrade proxy.
No multi-sig holding fees — protocol fees are routed to a separate immutable contract.
No backend custody — our servers never receive private keys or signed transactions.
Verifiable on-chain — every escrow address is publicly visible. You can watch your own.

↳ self-verifiable

Don't trust us — verify. Every contract address and source code is published on Etherscan with matching bytecode hashes. Run our circuits locally and you'll get the same proofs.

06 ↘

Multi-chain deployment

Middn contracts are deployed on EVM-compatible chains and Solana. Cross-chain trades are supported via atomic HTLC bridging — funds never leave the source chain prematurely.

Ethereum

Base

Arbitrum

Optimism

Polygon

Solana

More chains are added based on community demand. The contract logic is identical across EVM chains — only the deployment address differs.

07 ↘

Security audits

Middn contracts and circuits have been independently audited by two firms with deep cryptography and smart contract expertise.

Auditor	Scope	Date	Status
Trail of Bits	Escrow contracts	Mar 2026	Passed · 0 critical
Halborn	ZK circuits + crypto	Apr 2026	Passed · 0 critical
Code4rena	Public contest	Ongoing	Open · $250k pool

Full audit reports are linked in the project repository. We publish all findings — including informational notes — and every fix is verifiable in the commit history.

08 ↘

Read the whitepaper

The full whitepaper covers everything above in detail — circuit specifications, threat models, formal verification results, and economic security analysis.

Middn Whitepaper v0.1

PDF · 48 pages · 1.2 MB · May 2026

Download ↓

Source code, circuits, and contracts are all open-source under MIT. Pull requests welcome.

GitHub → Etherscan → Discord →

The Middn whitepaper.