Witness Chain

Welcome to the world of Watchtowers! Watchtowers are a group of nodes that can trigger fault alerts to maintain the security and consistency of the chain. Transactions between optimistic L2s and the L1s that they eventually settle on are the first line of defense for rollups. Optimistic roll-ups can be subject to unique types of denial of service and delay attacks as they make commits to both the L1 and L2. Witness chain incentivizes an operator network through Eigen Layer to prevent these attacks and trigger fault alerts notifying others to an attack/problems on the chain. Additionally, Witness Chain has some pioneering programs Proof of Geography, Proof of Backhaul (bandwidth), and Proof of Service that it is testing with this operator set, and will bring more value to it. This is one of the more unique use cases we have had the opportunity to study at Eigen Hub. Let’s dive in!

Eigeneers Start Here!

Without Witness Chain the entire process above is quite permissioned and centralized at many levels. Many roll ups perform the above duties with white listed validators for example. Witness Chain aims to change this paradigm empowering clients to use Eigen Layer’s permissionless, provably decentralized, and scalable validator set. So first let’s break it down for restakers, node operators, and then we will dive more deeply into the Witness Chain AVS. If your in a hurry you can just check which role you fill best!

Re-stakers

The node operator you restake with will be running an archive node for the L2 that it is “watching” as a watch tower. Native eth or any liquid staking token is probably what is best here but any service using witness chain No need to over complicate things there.
We need to talk a little about dual staking, a unique tool that Eigen gives AVS and their restakers. There wasn’t anything in the Witness Chain docs about dual staking at this time, and it isn't needed right now. Dual staking is mostly used for boot strapping a network and its token. OP, Arbitrum, and Coinbase are the only chains on test net right now. These established chain are well past the boot strapping phase. However, if a smaller and less established chain wanted to use Witness Chain’s watch towers this could be a point where they could get some utility for the smaller chains token. Simply require some of the new token to be staked to run the avs or the archive node. It would add friction but if the reward is great enough restakers would comply.

Operators

You have to be an Eigen Layer node operator
Rewards: Paid for up time participation in “Proof of Diligence” every L2 block.
Currently, no minimum stake required
Run multiple nodes from one Eth wallet with your Watchtower address
To operate a watch tower you will need to operate the watch tower software, which is very light <100MB, and an L2 archive node, which is comparativly quite heavy.
L2 achive nodes are a lot lighter than L1 archive nodes but are still substantial. Currently operators may service Arbitrum, OP, and Base. At the bottom of this list are their minimum hardware requirements.
This is actually the first modular structure Eigen Hub has seen that incentivizes running an archive node. Archive nodes are hardware intensive and only done by a few ecosystem players that need to retrieve the data, like Etherscan. Perhaps with a Witness Chain incentivized archive node structure, we might see new use cases crop up.
Witness chain has 3 unique protocols that utilize and incentives operators on their network. Proof of location, Proof of Backhaul, and Proof of Service. Read about them at the bottom of this article, they will all have incentives, currently in beta.
Click the toggle list for the recommended hardware specs for a Witness Chain node. These may be tested and revised in the future. Updated (03/08/2024)

Minimum Hardware Requirements Updated (03/08/2024)

4+ cores CPU
Must be SSD - 1 tb+ of free space
16GB + RAM
200+ Mbps Network Bandwidth

Minimum L2 archive node hardware specs Updated (03/08/2024)

Minimum 16 GB RAM for NOVA an 32 GB + for classic nodes
SSD drive with at least 2 TB free
16GB of RAM for Nitro and 32GB+ for Classic nodes
4+ core CPU,
SSD storage—8TB for Arbitrum One and 1.55TB for Arbitrum Nova, with monthly growth rates of about 0.67TB and 0.3TB, respectively.
16GB RAM
4TB SSD
Reasonably modern CPU such as
Intel's Core i5, i7, or i9 from the 8th generation onwards. AMD's Ryzen series from Ryzen 5 and above. Lower generations that this might work too but one could run into performane issues.

Witness Chain a deeper dive

This is a technical overview for some of the protocols witness chain makes possible, for more info please see the section labeled sources below.

Currently, Optimistic Rollup chains that support fraud proofs settle their state to Ethereum. Validators, post claims about the L2 state they have verified to a smart contract. Once a claim is confirmed, that L2 state is considered correct on Ethereum. During a time window, other **usually white listed (**👎 centralized) validators can challenge these claims, and a dispute resolution process occurs. This validation process is why assets move between optimistic chains and Ethereum L1 with a multi-day delay, OP currently has a 7 day delay. A challenge protocol involves parties submitting fraud proofs to Ethereum to determine the correct result of L2 execution within the time window. Witness Chain incentivizes a network so that they are always checking these claims and each other for appropriate behavior. We will dive into all this and the Proof of Backhaul, Geography, and Proof of Service below.

Current L2 architecture relies on the rollup noticing there is a problem before beginning the dispute mechanism. It is similar to the graphic on the left, only activated when something is noticed. Witness chain seeks to add another layer to rollup architecture. By adding watchtowers the system will be vigilant to any malfeasance from market participants at any time, automatically punish said malfeasance, and reward watchers.

Proof of Diligence

But who watches the watcher towers? The age old question, well Witness Chain has an answer. Their innovative “Proof of Diligence” nodes in the watchtower network are constantly mining diligence bounties to prove they aren’t sleeping on the job or aren’t nefarious actors! All through a trust free protocol. Proof of Diligence is trustless, validators must submit a proof every block of the L2 to show they did their job. This is currently limited to OP stack based L2 chains like Base or OP itself

Proof of Backhaul

Protocol that checks to see if a provider has a required amount of bandwidth. You have probably seen centralized versions from services such as Ookla. The centralized service maintains expensive servers all over the world to accomplish this task. Proof of Backhaul is a cheaper decentralized alternative to this for users or companies that need an accurate measurement of a providers bandwidth. Node operators act as challengers and test a provider to verify a required bandwidth. There is NO need to trust any of these decentralized challengers. Where as with centralized services etc. you must trust that they are accurate and aren’t data mining during the speed test. Challengers are paid for the challenge after it is recorded on the blockchain. Payers could be users but will most likely be companies and maybe even other computers such as AI to verify their decentralized compute to accomplish their task.

Proof of Service

Cellular service providers and users have misaligned incentives as the user cannot trust the provider to always be honest about the services charged for. Proof of service remedies this through a trust free method where both parties can asses the service individually through posts to the block chain and reconcile the service agreements. Node operators paid for recording the service agreement on the block chain.

Proof of Location (Knowloc)

Witness chain has an built in proof of geography by measuring the latency of watchtower nodes on their network called Knowloc. By measuring the time it takes to ping servers from a known location Knowloc can know where you are geographically, giving AVS a way to provably decentralize their node set geographically. Operators in under served regions could get more incentives for their operations.

BE CAREFUL

Don’t use a VPN if you choose to operate a watch tower for Witness Chain, there was no mention of slashing VPNs that defy Knowloc. HOWEVER, the protocol needs your true location and defeats VPNs so it is possible for there to be a negative incentive in the future.