Light

random

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Celestia

<h2 id="a-different-question-at-the-heart-of-celestia">A Different Question at the Heart of Celestia</h2>
Most blockchain light clients rely on full nodes to tell them whether block data has been published. <a href="https://x.com/Celestia" rel="noopener noreferrer nofollow">@Celestia</a> takes a different approach. <cite>Data availability answers one question: has this data been published? A node verifies this when it receives a new block being added to the chain.</cite> Rather than trusting fuller nodes at their word, Celestia gives light nodes a way to check for themselves.
<cite>Data availability sampling (DAS) is a process where light nodes request a random sample of block data, allowing them to verify that the block data is available without downloading the entire block.</cite> That distinction matters. <cite>While full nodes can verify a block by fully downloading it, light clients traditionally have no such mechanism since they only download the block header. DAS provides a method to verify data availability without downloading the entire block, letting them retain minimal resource requirements.</cite>
<h2 id="how-the-sampling-mechanism-works">How the Sampling Mechanism Works</h2>
The process rests on a specific encoding scheme. <cite>Block data is split into k x k chunks arranged in a matrix and expanded with parity data into a 2k x 2k Reed-Solomon encoding matrix, producing independent Merkle roots calculated from rows and columns. These Merkle roots form the block data commitments stored in the block header.</cite>
<cite>Every light node randomly chooses a set of unique coordinates in the extended matrix and queries bridge nodes for the data shares and the corresponding Merkle proofs at those coordinates.</cite><cite>Light nodes conduct multiple rounds of this random sampling, with each completed round increasing confidence that data is available. Once a node reaches a predetermined confidence level, such as 99%, it considers the block data available.</cite>
A block producer attempting to withhold data faces a structural problem. <cite>Every received data share with a correct Merkle proof is gossiped to the network.</cite> Enough unique samples across honest nodes means the full block can be reconstructed, making a withholding attack self-defeating.
The scalability implication runs counter to the usual logic. <cite>Data availability sampling enables light nodes to contribute to both the security and throughput of the network with significantly cheaper hardware than that of full nodes.</cite> More light nodes participating in sampling collectively supports larger blocks rather than adding load.
There are assumptions to keep in mind. <cite>Light nodes performing DAS must have a guarantee that the sampled data is erasure coded correctly. In Celestia, light nodes can be notified of a maliciously encoded block through Bad Encoding Fraud Proofs (BEFPs).</cite> That mechanism depends on connectivity. <cite>Light nodes must be connected to at least one honest full node to receive fraud proofs for incorrectly erasure coded blocks. If a light node is not connected to an honest full node, it cannot verify that the block has been improperly constructed.</cite> Eclipse attacks, which cut a node off from honest peers, can break that guarantee.
Sources: <a href="https://docs.celestia.org/learn/celestia-101/data-availability/" rel="noopener noreferrer nofollow">Celestia Docs: Modular Data Availability Layer</a> <a href="https://celestia.org/glossary/data-availability-sampling/" rel="noopener noreferrer nofollow">Celestia Glossary: Data Availability Sampling</a> <a href="https://l2beat.com/data-availability/projects/celestia/no-bridge" rel="noopener noreferrer nofollow">L2BEAT: Celestia Data Availability</a>

Celestia light nodes verify that a block's data was published without downloading it

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