Sereno

MLH Midnight Hackathon · July 2026 · DeFi track

¡…y sereno! Private rails. Accountable edges.

Named for the colonial sereno of Buenos Aires — the night watchman who walked the city at midnight and called that all was well. Sereno is a shielded remittance corridor on Midnight: families keep their privacy; designated auditors get cryptographic answers, not a spreadsheet of everyone.

Open repository See transaction proof
Network
Midnight Preprod
Language
Compact 0.23 · Halo2
Circuits
shield · transfer · unshield · disclose

The false choice

Formal rails

High fees, slow settlement, total surveillance. Every counterparty and amount becomes someone else’s data exhaust.

Informal rails

Cash couriers and opaque P2P. No compliance story, no consumer protection — and a growing regulatory target.

Neither extreme is acceptable for LatAm remittances. Sereno draws a third line.

Architecture

Private in the middle.
Public only where it must be.

  1. shield Entry is accountable

    Deposit amount is public. A hiding note commitment lands in a Merkle tree. TVL increases.

  2. transfer Interior is private

    Public sees commitment + nullifier only. Auditor gets an in-circuit ElGamal ciphertext of the amount.

  3. unshield Exit is accountable

    Withdrawal amount is disclosed. Note is spent. TVL decreases.

  4. disclose Audit on request

    Owner proves in-circuit that a commitment opens to a concrete amount — keyed by audit request id. Note not spent.

Midnight Preprod · funded wallet · circuits compiled

Proof of transactions

Hackathon demo wallet funded on Midnight Preprod. Use these artifacts for judging.

Unshielded wallet

mn_addr_preprod1c2ljvsln2z5aca6nmd44skj72kmdavnm03vm9v3rwm37kclfnptsffuh6t

Contract toolchain
  • Compact compiler 0.31.1
  • 4 circuits compiled with prover/verifier keys
  • Local proof server · Docker · port 6300

Elevator pitch · ~30 seconds

“Latin American remittances force a bad trade: surveillance or the black market. Sereno is a shielded corridor on Midnight — private transfers in the middle, public amounts only when money enters or leaves the pool, and a designated auditor who can decrypt transfer amounts or request an in-circuit note opening. Named for the night watchman of Buenos Aires who called ‘y sereno’ at midnight: order without turning on every light.”

Why Midnight

Compact makes commitments, Merkle trees, and private witnesses first-class. Client-side proving; the chain never sees interior amounts except at deliberate edges.

Why now

Argentina’s Ley 27.739 puts VASPs under UIF reporting. Compliance-by-design beats “hold everyone’s data forever.”

What we shipped

Full Compact contract + TypeScript CLI + Windows/WSL runbook + this site. Apache-2.0.

Clone, compile, prove.

git clone https://github.com/leocagli/sereno.git

GitHub · leocagli/sereno SETUP.md (WSL2)