## Cryptology ePrint Archive: Report 2019/1139

Coded Merkle Tree: Solving Data Availability Attacks in Blockchains

Mingchao Yu and Saeid Sahraei and Songze Li and Salman Avestimehr and Sreeram Kannan and Pramod Viswanath

Abstract: In this paper, we propose coded Merkle tree (CMT), a novel hash accumulator that offers a constant-cost protection against data availability attacks in blockchains, even if the majority of the network nodes are malicious. A CMT is constructed using a family of sparse erasure codes on each layer, and is recovered by iteratively applying a peeling-decoding technique that enables a compact proof for data availability attack on any layer. Our algorithm enables any node to verify the full availability of any data block generated by the system by just downloading a $\Theta(1)$ byte block hash commitment and randomly sampling $\Theta(\log b)$ bytes, where $b$ is the size of the data block. With the help of only one honest node in the system, our method also allows any node to verify any tampering of the coded Merkle tree by just downloading $\Theta(\log b)$ bytes. We provide a modular library for CMT in {\sf Rust} and {\sf Python} and demonstrate its efficacy inside the {\sf Parity Bitcoin} client.

Category / Keywords: foundations / blockchains, light nodes, fraud proofs, Merkle tree, information theory