Celestia serving as off-chain DA for Ethereum rollups 🧵


The main reliance that rollups have on L1 is the cost of calldata and its data throughput. While Ethereum is in the process of implementing its sharding solution, rollups should have a source of cheap data…

and high data throughput to alleviate some of their near-term scaling bottlenecks. While transaction fees can become cheaper when amortized among a larger batch, there is a point at which the fee decline reaches diminishing returns.

This is where volitions and validiums come to alleviate the problem. Volitions are a type of zkRollup that give users the option to post their transaction data on-chain or off-chain. Similarly, a validium is a zkRollup construction that only has off-chain data availability.

What Celestia can supply to volitions and validiums is a source of cheap and scalable data availability that allows them to provide cheaper transactions to their users.


How this would work is the result of the Quantum Gravity Bridge. 
https://blog.celestia.org/celestiums/

When transactions would be submitted by the validium to Celestia, the validators would check data is available and come to consensus on ordering to publish it to the network. To ensure that the Ethereum verifier contract is aware that data is available on Celestia….

a Merkle root of available data would be signed by 2/3 of the validator set. The signatures for the data would then be sent to a DA contract on the gravity bridge that interacts with the Ethereum verifier contract.

Once the DA contract has received and verified the signatures from the validator set the Ethereum verifier contract would check the signatures attesting to data availability that correspond to the validity proof it verified.

Read more about the Quantum Gravity Bridge for off-chain data availability 👇

https://blog.celestia.org/celestiums/

How Celestia can provide off-chain data availability for Ethereum L2s

The Ethereum data availability landscape 🧵

With the rapid growth of L2s, a spectrum of data availability solutions have emerged ranging from off-chain to on-chain DA layers.

How do the cost and security tradeoffs of different DA solutions compare?
https://blog.celestia.org/ethereum-off-chain-data-availability-landscape/

Pure validiums

A validium uses zero knowledge proofs for transaction validity and stores transaction data off-chain with a central data provider.

Pure validiums represent the cheapest and least secure in this spectrum

Data availability committees (DACs)

Rather than a single provider, a committee is entrusted with providing data availability to the network.

If the committee were to act maliciously, they could freeze or steal all funds on the chain and kill the chain’s liveness entirely.

Celestium

A Celestium is an L2 chain that leverages Celestia for data availability, but uses Ethereum for settlement and dispute resolution.

The validator set of Celestia is akin to a permissionless DAC but with economic security guarantees in the form of slashing.

Ethereum rollups

Rollups that leverage Ethereum’s on-chain data availability inherit the highest DA guarantee at the highest cost. 

For users that desire lower cost, other off-chain DA options will be available, including Celestiums.

To learn more about Celestiums, check out our recent blog post and thread here 👇
https://twitter.com/CelestiaOrg/status/1491129074341019649

The Ethereum data availability landscape

Sovereignty and communication between chains 🧵

Blockchains that are sovereign have freedom to choose their preferred execution environment. A sovereign blockchain on Celestia has no restrictions imposed on it, giving it the ability to upgrade or fork if necessary.

Ultimately a sovereign chain can make changes in accordance with its own social consensus, independent of Celestia or any other chain.

As such, these blockchains on Celestia are flexible in design possibilities. They can be composable shared environments for many applications…

or single instance applications that don’t require composability with other applications. What Celestia’s shared security provides is that clusters of blockchains can be created which facilitates trust-minimized communication between them.

Communication within the same cluster, and between different clusters have distinct properties.

Intra-cluster: Can communicate between chains in the same cluster in a trust-minimized way.

Inter-cluster: Can communicate between chains in different clusters by relying on a third party to facilitate communication.   

Inter-cluster bridging typically involves a third party, like a committee, to operate the bridge, which is common among current bridge designs.

IBC is also an example of inter-cluster bridging that doesn't require a third party.

It instead uses light clients to track the consensus of an opposite blockchain.

Once a block header has been verified as valid, the state is then checked to see if it is stored on the chain by verifying a proof, such as a Merkle proof.

This allows the two chains to communicate with an honest majority assumption of their existing validator sets, as opposed to introducing a third party.

An example of intra-cluster communication is the bridges that rollups use with their parent chain.

What makes them trust-minimized is that they are validating bridges, where they use either fraud or validity proofs.

While the security profile of trust-minimized bridges is optimal, only rollups are capable of such bridges. Other chains require stronger trust assumptions for bridging, like an honest majority assumption.

Ultimately, many blockchains on Celestia will be sovereign with the ability to communicate via mechanisms that are suitable to their own security and trust preferences.

An intro to cross-chain communication

Discussion on shared security featuring @zmanian, @musalbas and @jadler0 happening now!

Read the thread for tweets from the livestream 👇
https://twitter.com/i/spaces/1OdKrBbAXnAKX

"Blockchain security comes down to the question 'who can rug you?' How many actors need to collude to attack the system?" -@zmanian

@zmanian "A system with shared security has the property that in order to break one chain, you need to break them all." -@musalbas

@zmanian @musalbas "Until Celestia came along, the idea of a very scalable system of multiple chains with shared security was very hard." -@zmanian

@zmanian @musalbas "Celestia provides the core primitive that chains require to establish shared security—data availability." -@musalbas

@zmanian @musalbas "Cosmos’ interchain staking and Polkadot’s parachain slots models only scale to the order of 100s of chains.

In Celestia we see a world of millions of blockchains." -@musalbas

@zmanian @musalbas "The most important part of these systems is who can propose a block, and who can verify the state.

These core properties of a blockchain — censorship resistance and auditability — are what data availability provides." -@zmanian

@zmanian @musalbas "The real limitation on how many transactions a blockchain can process is I/O. Decoupling data availability from the I/O process is the only way that we’ll be able to produce petabytes of secure block space." -@zmanian

@zmanian @musalbas "The theoretical limit of safety of shared security is better, but the actual applied practical security at this moment is still in favor of Tendermint chains + IBC." -@zmanian

@zmanian @musalbas "Creating a DAO on ethereum is like incorporating under the law of a certain country.

The future model for blockchains I see is where each app has its own chain. In that model I see hard forks as a feature for social coordination." -@musalbas

“Scalability of a chain is measured by the throughput divided by the cost for an end user to verify it.” -@musalbas

“The invention of personal computers allowed individuals to be sovereign. The invention of blockchains allow communities to be sovereign.” -@musalbas quoting @buchmanster

“The combination of rollups, data availability and modular blockchains is one of the most exciting things happening in the space right now.” -@zmanian

Best quotes from the shared security space with Zaki Manian

The benefits of modular blockchains 🧵

Modular blockchains are the result of separating the core components of a single blockchain and running them on separate layers.

Here’s what makes them powerful 👇

Scalability

Layers that specialize on a couple of core components allows for greater scalability innovations without the burden of making tradeoffs that come with a modular blockchain. For example, a modular DA layer with DA sampling can scale linearly with the number of users.

Interoperability

Blockchains can utilize a modular shared security layer, like Celestia, to enable trust-minimized bridging between blockchains in the same cluster. This increases both the security and ease at which blockchains can communicate with each other.

Bootstrapping costs

New blockchains can be effortlessly created with minimal cost and time spent. Rollup SDKs, like Optimint, will not only help facilitate this but provide a way to bootstrap without needing a consensus mechanism, large validator set, or token distribution.

Experimentation

Blockchains can be effortlessly created and used to experiment with new innovative technologies that bring further scalability and optimizations to the entire stack. This allows them to focus directly on the key elements they want to innovate on.

The benefits of modular blockchains

How does Celestia solve the data availability problem? 🧵

The data availability problem is concerned with whether data in the most recent block is hidden or available. This is important because by hiding block data, rollup operators can commit fraud or steal funds.

To prevent such an attack, the complete block data must be available for anyone to download.

A naive way to verify data availability is for full nodes to download the entire block, but this introduces high requirements for full nodes and limits the scalability of the network.

Celestia uses a clever scheme that allows light clients to verify data availability without needing to download the entire block.

This means that you can verify data availability with a small computer – in fact you can even do it on your smartphone! 🤯
https://twitter.com/musalbas/status/1480901457633239048?s=20

How? Data availability sampling.

Instead of downloading the entire block, Celestia light nodes just download small random samples of data from the block.

If all the samples available, then this serves as proof that the entire block is available.

If they aren’t able to download a sample then the block is unavailable.

Erasure coding is a cryptographic tool fundamental to data availability sampling, which helps to increase the difficulty that a block can be made unavailable.

This is done by replicating the data, which expands the block’s size. 

For example, if a block contains 50% original data and 50% replica data, more than 50% of the block’s data would need to be withheld to make data unavailable...

as the original data can be recovered with only 50% of the block.

With data availability sampling and erasure coding, minimal hardware is required for light nodes to contribute to both the security and throughput of the chain.

Read more about the data availability problem and its solutions here 👇
https://coinmarketcap.com/alexandria/article/what-is-data-availability

Celestia and the data availability problem

The multi-chain future is likely one that encompasses the idea of sovereign “clusters” of blockchains that can bridge to each other in a trust-minimized way.

Trust-minimized bridging is facilitated by the chains sharing security with a common data layer like Celestia. https://twitter.com/VitalikButerin/status/1479501366192132099 

An example of this is a rollup and its parent chain. With trust-minimized bridging funds can’t be stolen directly from the bridge.

This is the opposite for bridging between clusters where funds can be stolen by the committee that operates the bridge, like the ETH-Polygon bridge.

Then why not have every chain run in the same cluster for shared security with trust-minimized bridging?

See @musalbas's thread here for why: 
https://twitter.com/musalbas/status/1444994755369177090

How does Celestia fit in a multi-chain future?
It provides the core piece for building clusters of chains, a modular data availability and shared security layer.

Sovereign clusters of chains can easily bootstrap and deploy on Celestia to utilize its scalable data availability.

Celestia itself is not a cluster of chains because it doesn't provide a smart contract environment, but rather multiple clusters of chains can exist *on top of Celestia*, by using Celestia as the base data availability and consensus layer.

They will also be able to conduct trust-minimized bridging with other chains in the same cluster on Celestia because they will inherit the security of Celestia’s validators. 

To learn more, see this article about clusters of chains and bridging 👇
https://blog.celestia.org/clusters/

The future of bridging in a multi-chain ecosystem

Celestia light nodes 🧵 
Why they’re more secure than typical light clients and how they help to scale and secure the network.

Light clients are important in a blockchain network to allow individuals to participate as a non-consensus node without the overhead of full nodes.

Light clients typically only download block headers, and don’t verify transactions themselves. This gives them weak security guarantees compared to full nodes as they rely on an honest majority assumption and assume the chain is valid by default.

Celestia light clients have stronger security guarantees and engage in processes that secure the network. Because Celestia light clients have practically the same security as full nodes and take an active role in securing the network, we call them “light nodes.”

The magic that powers light nodes is called data availability sampling. Data availability sampling is a process where light nodes request a random sample of block data. This allows light nodes to verify that the block data is available without downloading the entire block.

Turning an honest majority assumption for a light client into a minimum number of light nodes assumption, and a one honest full node assumption. This allows Celestia light nodes to contribute to the throughput and security of the network with lower hardware requirements.

Learn more about data availability sampling in this post by @musalbas on the @CoinMarketCap blog 👇https://coinmarketcap.com/alexandria/article/what-is-data-availability