RFC-0500/PaymentChannels

Payment channels

status: draft

Maintainer(s): Cayle Sharrock

Licence

The 3-Clause BSD Licence.

Copyright 2019. The Tari Development Community

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

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Language

The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY" and "OPTIONAL" in this document are to be interpreted as described in BCP 14 (covering RFC2119 and RFC8174) when, and only when, they appear in all capitals, as shown here.

Disclaimer

This document and its content are intended for information purposes only and may be subject to change or update without notice.

This document may include preliminary concepts that may or may not be in the process of being developed by the Tari community. The release of this document is intended solely for review and discussion by the community regarding the technological merits of the potential system outlined herein.

Goals

Related Requests for Comment

Description

Introduction

The base layer is slow. The DAN is fast. However, every DAN instruction that results in a state change has a fee (i.e. base layer transaction) associated with it.
To bridge the speed gap between the two layers, a payment channel solution is required.
This document provides the high-level overview of how this is done.

The Clacks

The Clacks is a multi-party side-channel off-chain scalability proposal for Tari. The essential idea behind the Clacks is:

  • Users give control of some Tari to a Clacks Committee.
  • The committee creates an off-chain UTXO for the user(s). This is called the peg-in transaction.
  • Users can transact amongst each other without those transactions touching the base layer. This allows a very high throughput of transactions and instant finality. However, the locus of trust move significantly towards the Clacks committee. In other words, base layer transactions are slow, but do not require users to trust anyone. Clacks transactions are fast, but requires some level of trust in the entity or entities controlling the user's funds.
  • Users can send off-chain Tari to any other users, including users that have not made deposits into the Clacks committee.
  • Users can request a withdrawal for their Tari at any time. At predefined intervals, the Clacks committee will process those withdrawal requests and give the Tari UTXO control back to the user.

Users also have a pre-signed, time-locked transaction that returns the user's fund back to them. This refund transaction can be used in case the Clacks committee stops processing withdrawals and provides insurance for users against having their funds locked up forever.

The peg-in, peg-out cycle are represented by standard Tari transactions. This means that full nodes verify that no funds have been created or destroyed over the course of the cycle. They do not check that the "balances" associated with users are what those users would expect in an honestly run side chain.

However, if the side-chain is run as a standard mimblewimble process, any third party running a full node and that access to the opening and closing channel balances, can in fact verify that the committee has operated honestly.

More discussion and technical details for the Clacks can be found in the white paper.