Demo

You need a small amount of testnet ETH on Arbitrum Sepolia to pay transaction fees. The Alchemy faucet is the most reliable source — 0.001 ETH per drip, enough for several transactions.

Faucet: alchemy.com/faucets/arbitrum-sepolia

Alternative: sepoliafaucet.com (Ethereum Sepolia) then bridge to Arbitrum Sepolia via bridge.arbitrum.io. Bridging from Sepolia → Arbitrum Sepolia takes ~10 minutes.

If your MetaMask doesn't have Arbitrum Sepolia yet, add it manually or click "Add Network" from the vault interface. Network parameters:

• Network name: Arbitrum Sepolia
• RPC URL: https://sepolia-rollup.arbitrum.io/rpc
• Chain ID: 421614
• Currency symbol: ETH
• Block explorer: https://sepolia.arbiscan.io

Once connected, open sunima.uk/vault and click "Connect Wallet". Approve the MetaMask connection prompt. Your wallet address should appear in the top-right corner.

Enter an amount (e.g. 0.01 ETH) into the Deposit field. Click Deposit. MetaMask will prompt you to approve two transactions:

• Transaction 1: your client encrypts the amount under the organizer's 2048-bit Paillier public key. The ciphertext is submitted to the vault contract.
• Transaction 2: the contract adds the ciphertext to your existing encrypted balance via E(a) + E(b) = E(a+b) — no decryption required. ETH is transferred into the vault.

After confirmation, your on-chain balance is a ciphertext. Block explorers show that you deposited, not how much.

Enter a withdrawal amount. Click Withdraw. The flow:

• Your client requests a withdrawal for a specific amount (not the full balance).
• The organizer signer (operated by Sunima core team) verifies the request is within your encrypted balance, signs the authorization, and relays it to the contract.
• The contract subtracts the ciphertext of the withdrawal amount from your encrypted balance and transfers plain ETH to your wallet.

Current trust model: the organizer is a single signer operated by Sunima core team. Stage 4 will replace this with a FROST threshold-MPC committee (currently a 2-of-3 proof-of-concept; a production k-of-N committee is not yet built) — see Architecture §6.

Enter a recipient address and an amount. Click Transfer. The client encrypts the transfer amount under the organizer's public key; the contract simultaneously subtracts from your encrypted balance and adds to the recipient's — both operations are additive homomorphic.

Observers on Arbiscan see: sender wallet, recipient wallet, a ciphertext blob. They cannot see the transfer amount, the sender's balance, or the recipient's balance. Two wallets visibly interact; the value between them is encrypted.

This is Paillier additive privacy. Stage 2 — also live, on Arbitrum Sepolia at 0x3a0d9A52416847D984a17D0dBe849cdF6492209E (v0.7.1) — routes balance arithmetic through EC-ElGamal on BN254 for measured 12–18× lower gas vs the Paillier vault on the same network. Stage 3 — closed (May 2026) — adds the on-chain TFHE attestation verifier SunimaTFHEPredicatesV3 at 0x1840e8E2EF53e8AaA846941aa628d7bd70E27396, with an off-chain Rust worker (Zama tfhe-rs v1.6.0) signing EIP-191 attestations for encrypted range / compare / conditional predicates; on-chain verifyAndConsume* measured at ~33K gas median. Stage 4 will decentralise the organizer via a FROST threshold-MPC committee (currently a 2-of-3 proof-of-concept; production k-of-N not yet built).