leanDA quantum-resistant sampling, data checks that stay safe against quantum computers
Strawmap J* (2028~29) · leanDA PQ sampling
This rebuilds data availability sampling, which checks that the blob data posted by rollups was actually published by examining only a small random part of it, on a hash-based method that quantum computers cannot break. The KZG commitments used today are vulnerable to quantum computers.
Why it is needed
Ethereum is moving toward a model in which, instead of every node downloading the full blob data that rollups post, each node randomly picks a few small pieces and checks them. This method, in which the whole is trusted to have been published if all the sampled pieces come back correctly, is Data Availability Sampling. For it to be safe, a proof is needed that each piece is part of the original. Today this uses KZG commitments, which are based on elliptic curve mathematics. Elliptic curve cryptography has the problem that it breaks against a sufficiently large quantum computer. Once quantum computers become practical, fake pieces could be made to look genuine, opening a way to pretend data exists when it does not. leanDA is the data layer of the lean Ethereum vision pushed by the Ethereum Foundation, and it is research into redesigning this sampling on hash functions that quantum computers cannot break. However, a hash-based commitment cannot directly guarantee, as KZG does, that the erasure coding, which extends the data so it can be reconstructed, was done correctly. How to prove this separately is the core challenge. The concrete design is still at the research stage and may change, and the Strawmap placement in 2028 to 2029 is not a confirmed schedule either.
How it works
- Extend the data The blob is extended with erasure coding so that the original can be reconstructed from just a portion of the pieces. Even if someone withholds some of them, the rest are enough to recover it.
- Pick pieces and check them Each node requests a few pieces at random and receives with each piece a proof that it belongs to the original. If all the requested pieces arrive, it judges that the data was published.
- Make the proof quantum-resistant This proof is built on hash functions instead of elliptic-curve-based KZG. Hash functions are known to be hard to break even with quantum computers, which prevents fake pieces from being forged.