Coded blockchains have acquired prominence as a promising solution to reduce storage costs and facilitate scalability. Within this class, Luby Transform (LT) coded blockchains are an appealing choice for scalability owing to the availability of a wide range of low-complexity decoders. In the first part of this work, we identify that traditional LT decoders like Belief Propagation and On-the-Fly Gaussian Elimination may not be optimal for heterogeneous networks with nodes that have varying computational and download capabilities. To address this, we introduce a family of hybrid decoders for LT codes and propose optimal operating regimes for them to recover the blockchain at the lowest decoding cost. While LT coded blockchain architecture has been studied from the aspects of storage savings and scalability, not much is known in terms of its security vulnerabilities. Pointing at this research gap, in the second part, we present novel denial-of-service threats on LT coded blockchains that target nodes with specific decoding capabilities, preventing them from joining the network. Our proposed threats are non-oblivious in nature, wherein adversaries gain access to the archived blocks, and choose to execute their attack on a subset of them based on underlying coding scheme. We show that our optimized threats can achieve the same level of damage as that of blind attacks, however, with limited amount of resources. Overall, this is the first work of its kind that opens up new questions on designing coded blockchains to jointly provide storage savings, scalability and also resilience to optimized threats.

翻译：编码区块链作为一种降低存储成本并促进可扩展性的有前景方案，已获得广泛关注。在此类方案中，Luby Transform (LT) 编码区块链因具备多种低复杂度解码器而成为实现可扩展性的理想选择。在本研究的第一部分，我们发现传统LT解码器（如置信传播解码和即时高斯消元解码）可能不适用于具有不同计算与下载能力的异构网络节点。为此，我们引入了一类LT码混合解码器，并提出了其最优工作区间，以实现以最低解码成本恢复区块链。虽然LT编码区块链架构已在存储效率与可扩展性方面得到研究，但其安全脆弱性尚未被充分认知。针对这一研究空白，在第二部分中，我们提出了针对LT编码区块链的新型拒绝服务威胁，该威胁通过针对具有特定解码能力的节点，阻止其加入网络。我们提出的威胁具有非盲目性特征：攻击者通过访问已归档区块，并基于底层编码方案选择其中部分区块实施攻击。研究表明，优化后的威胁能以有限资源实现与盲目攻击同等的破坏效果。总体而言，本研究开创性地提出了编码区块链设计的新问题，即如何协同实现存储优化、可扩展性及对抗优化威胁的鲁棒性。