Non-Custodial
by Design

FROST MPC — 2-of-2 Threshold Signing

No complete private key exists anywhere. Signing requires cooperation from at least two parties.

On-Chain Atomic Fee Splitting

User funds never pass through a BitVoy address. Based on the content the user signed, the payment contract (PaymentRouter) distributes directly to the merchant and fee recipient within a single transaction.

What this design guarantees

For details on signature methods, contract functions, and per-mode breakdown, see Appendix: Technical Details.

Gas Sponsorship by BitVoy

In gasless modes, the Relayer pays gas in native tokens. The Relayer only submits the signed content on-chain and cannot alter the transfer amount, recipient, or deadline. Gas is never deducted from the user's ERC-20 token balance. Gas sponsorship is BitVoy's service cost, not custody of user funds.

FAST & WC Modes

FAST mode uses the BitVoy wallet (MPC passkey), WC mode uses an external wallet (e.g. MetaMask). Signing occurs entirely within the user's own wallet. Final distribution is executed on-chain by the PaymentRouter in all modes.

Appendix: Technical Details

A. Signature Design and Relayer Permissions (FAST / WC eip3009)

Item	Detail
Signature content	EIP-3009 transferWithAuthorization with from = User, to = PaymentRouter, value = totalAmount
Nonce generation	keccak256(abi.encode(intentIdBytes32, payee, feeRecipient, totalAmount, feeAmount, deadline, chainId)) — bound to intentId, recipient, fee recipient, total amount, fee amount, deadline, and chain
Router behavior	When Relayer calls eip3009Pay(), the Router verifies the signature, withdraws totalAmount, and distributes to merchant and fee recipient via safeTransfer. If nonce and arguments don't match, reverts — Relayer cannot substitute recipient or amount
Relayer's holdings	Only native tokens for gas (no user funds)
Fee	totalAmount * 100 / 10000 (1%) — enforced on-chain

B. Tamper-proof mechanism by mode

Mode	Tamper-proof
FAST / WC eip3009	payee, feeRecipient, amounts etc. encoded in EIP-3009 nonce. Router reverts on mismatch
WC permit2 (USDT)	Payment content included in Permit2 Witness signature. Reverts on mismatch
WC approve	Amount and recipient enforced in Router.pay() calldata

C. Checkout Flow (Steps)

FAST (BitVoy wallet)

Step	Detail
1. Authentication	User performs passkey authentication (BitVoy MPC)
2. Typed data generation	Server generates EIP-3009 TransferWithAuthorization typed data (from = payer, to = Router, value = totalAmount, nonce = hash of checkout data)
3. Signing	Client signs via MPC passkey. BitVoy server cannot sign alone
4. On-chain submission	Relayer calls PaymentRouterV4_2.eip3009Pay(). For USDT, uses Permit2 Witness signature to call PaymentRouterV5_2.permitAndPay()
5. Distribution	Router distributes to merchant and fee recipient within the same transaction

WC (External Wallet)

Step	Detail
1. Page load	User opens the checkout page and selects a wallet
2. Connection	Connect to external wallet via WalletConnect
3. Sign / Submit	Depending on mode: (a) EIP-3009 signature → Relayer submits, (b) approve → pay (user submits), (c) Permit2 Witness signature → Relayer submits (USDT)
4. Distribution	Router distributes to merchant and fee recipient within the same transaction

On-Chain Contract Registry

All payment router contracts are trustless — no owner, no upgrade proxy, no admin key. Deployed bytecode is immutable and publicly verifiable on each chain's explorer.