Timeline Aggregation Protocol (TAP)

Overview

The TAP (Timeline Aggregation Protocol) facilitates a series of payments from a sender to a receiver (TAP Receipts), who aggregates these payments into a single payment (a Receipt Aggregate Voucher, or RAV). This aggregate payment can then be verified on-chain by a payment verifier, reducing the number of transactions and simplifying the payment process.

Key Components

• Sender: Initiates the payment.
• Receiver: Receives the payment.
• Signers: Multiple signers authorized by the sender to sign receipts.
• State Channel: A one-way channel opened by the sender with the receiver for sending receipts.
• Receipt: A record of payment sent by the sender to the receiver.
• ReceiptAggregateVoucher (RAV): A signed message containing the aggregate value of the receipts.
• tap_aggregator: A service managed by the sender that aggregates receipts on the receiver's request into a signed RAV.
• EscrowAccount: An account created in the blockchain to hold funds for the sender-receiver pair.

Security Measures

• The protocol uses asymmetric cryptography (ECDSA secp256k1) to sign and verify messages, ensuring the integrity of receipts and RAVs.

Process

1. Opening a State Channel: A state channel is opened via a blockchain contract, creating an EscrowAccount for the sender-receiver pair.
2. Sending Receipts: The sender sends receipts to the receiver through the state channel.
3. Storing Receipts: The receiver stores the receipts and tracks the aggregate payment.
4. Creating a RAV Request: A RAV request consists of a list of receipts and, optionally, the previous RAV.
5. Signing the RAV: The receiver sends the RAV request to the tap_aggregator, which signs it into a new RAV.
6. Tracking Aggregate Value: The receiver tracks the aggregate value and new receipts since the last RAV.
7. Requesting a New RAV: The receiver sends new receipts and the last RAV to the tap_aggregator for a new RAV.
8. Closing the State Channel: When the allocation period ends, the receiver can send the last RAV to the blockchain and receive payment from the EscrowAccount.

Performance Considerations

• The primary performance limitations are the time required to verify receipts and network limitations for sending requests to the tap_aggregator.

Use Cases

• The TAP protocol is suitable for systems that need unidirectional, parallel micro-payments that are too expensive to redeem individually on-chain. By aggregating operations off-chain and redeeming them in one transaction, costs are drastically reduced.

Compatibility

• The current implementation is for EVM-compatible blockchains, with most of the system being off-chain.

Contributing

Contributions are welcome! Please submit a pull request or open an issue to discuss potential changes. Also, make sure to follow the Contributing Guide.