Sereno

Private remittance rails. Accountable edges. Built on Midnight.

Named for the sereno — the night watchman of colonial Buenos Aires who walked the city at midnight and called “¡…y sereno!” when all was well.

MLH Midnight Hackathon — July 2026 · DeFi + AI tracks

Demo video (90s)	YouTube link — see Devpost submission
Live site	https://sereno-kappa-eight.vercel.app
Repository	https://github.com/leocagli/sereno
Elevator pitch	ELEVATOR-PITCH.md
Video script	PITCH.md
Windows setup	SETUP.md
Agent (AI)	cd cli && npm run agent:demo

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Elevator pitch (30s)

Latin American remittances force a bad trade: surveillance or the black market. Sereno is a shielded corridor on Midnight — private in the middle, public only at entry/exit, with a designated auditor who gets cryptographic answers, not everyone’s ledger. Order without turning on every light.

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The problem

Formal rails	Informal rails
High fees, slow settlement	Cheap, opaque
Total financial surveillance	Zero compliance story
Every amount is data exhaust	Growing regulatory target

Neither extreme works for families sending money home.

The solution

Sereno is a note-based shielded pool where:

Circuit	Public visibility
shield(amount)	Amount public (accountable edge)
transfer(recipientPk)	Private to public (commitment + nullifier). Auditor gets in-circuit ElGamal ciphertext of the amount
unshield()	Amount public on exit
discloseToAuditor(id)	Owner proves commitment opens to amount under an audit request — note not spent

Auditor public key is fixed at deploy. Not a backdoor for the operator — selective disclosure by design.

shield ──► [ Merkle tree of commitments + nullifiers ]
              │  transfer (private + ElGamal → auditor)
              ▼
           unshield / discloseToAuditor

Proof of transactions (Preprod)

Live network artifacts for judges:

Item	Value
Network	Midnight Preprod
Unshielded wallet	mn_addr_preprod1c2ljvsln2z5aca6nmd44skj72kmdavnm03vm9v3rwm37kclfnptsffuh6t
Faucet funding	5,000 tNIGHT
Transaction ID	00bc9da4d80c86b1b7805df25384ef87228111e56734f94d64bf9f7ef148a141ab
Faucet	https://faucet.preprod.midnight.network/
Explorers	preprod.midnightexplorer.com · midnight-preprod.subscan.io

Paste the tx hash into the explorer search to verify funding on preprod.

Toolchain proof (local)

Artifact	Status
Compact compiler	0.31.1 (CLI 0.5.1)
Circuits compiled	shield, transfer, unshield, discloseToAuditor + prover/verifier keys
Pure-circuit smoke	npm run smoke in cli/ — address, commitment, auditor key derivation
Proof server	Docker midnightntwrk/proof-server:latest · :6300

Honesty for judging: Full deploy / callTx against preprod depends on wallet-sdk sync stability with the public RPC (we hit intermittent isSynced / WS disconnects under Node). The cryptographic core is compiled; funding is live on preprod with the hash above. See SETUP.md to reproduce.

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Repository layout

sereno/
  contract/          Compact contract + witnesses (sereno.compact)
  cli/               TypeScript CLI (deploy / shield / transfer / …)
  web/               Landing page (Vercel)
  SETUP.md           Windows 11 + WSL2 runbook
  PITCH.md           2-minute video script
  ELEVATOR-PITCH.md  10s / 30s / 60s pitches

Quick start (WSL2)

# Proof server
docker run -d -p 6300:6300 --name midnight-proof-server \
  midnightntwrk/proof-server:latest midnight-proof-server -v

# Contract
cd contract && npm install && npm run build

# CLI
cd ../cli && npm install && npm run build
npm run smoke          # local pure circuits
npm run demo-sim       # offline corridor simulation
npm run agent:demo     # AI agent (tools, no secret keys) — dual-track script
npm run agent          # interactive agent REPL
npm run start          # interactive preprod menu

Privacy-preserving agent (AI track)

The agent is a tool-using operator over the Sereno corridor:

• Tools: deploy_corridor, shield, transfer, disclose_to_auditor, unshield, get_public_ledger, get_faucet_proof
• Never returns secret keys or note preimages — only public ledger fields and explicit audit disclosures
• PureCircuits (publicKey, noteCommitment, elGamalPublicKey) are real; callTx path is simulated when wallet sync is unavailable
• Natural language routing (ES/EN) without a cloud LLM (local policy agent) — optional LLM can wrap the same tools later

Full Windows notes: SETUP.md.

Contract surface (Compact)

• Ledger: HistoricMerkleTree commitments, nullifier set, sealed auditorPk, auditDisclosures, transferCiphertexts, totalValueLocked
• 1-in / 1-out transfers (same amount; splits on roadmap)
• Domain-separated hashes: sereno:owner:pk, sereno:nullifier

Cryptographic lineage

1. Zerocash — notes, commitments, nullifiers
2. Zcash viewing keys — auditor-directed visibility
3. Privacy Pools — accountable privacy on demand

Regulatory context (Argentina)

Ley 27.739 (2024) brought VASPs under AML/CFT, PSAV (CNV), and UIF reporting. Sereno’s public edges + selective disclosure are an architecture direction for compliance-by-design — not a claim of regulatory approval.

Roadmap

• Native shielded token plumbing for real value custody
• Multi-output transfers / change
• Web wallet UX (CLI is intentional MVP scope)
• Production auditor key ceremony

License

Apache-2.0 — see LICENSE.

Built during the MLH Midnight Hackathon, July 2026, against docs.midnight.network and official midnightntwrk examples.