Layer 2 is one of the most promising approaches to improve the scalability of blockchains. The idea is to shift some tasks (e.g., ordering and execution of some transactions) off the mainchain (i.e., layer 1) to reduce the workload of the mainchain. In this work, we study the so-called committee-based layer 2 approaches. Being conceptually similar to sharding, committee-based layer 2 approaches allow committees to order and execute transactions in parallel to further improve the performance of the system. Different from existing committee-based layer 2 solutions that often prioritize low latency over high throughput, our solution strives to achieve both low latency and high throughput. The technical building blocks include a lightweight primary-backup design for off-chain committees, an efficient on-chain lease management design for managing the primaries, and a one-phase solution for cross-committee transactions (i.e., transactions that need to be processed by multiple committees). Experimental results show that our solution achieves both low latency and high throughput and can be deployed on even low-end machines.

Byzantine agreement is the most fundamental primitive in distributed computing. All known Byzantine agreement protocols achieve quadratic or sub-quadratic messages and communication. We show that surprisingly, by directly assuming a random leader election oracle (that can be built from the verifiable random function), threshold signatures, and the$1/3$corruption bound, we can build Linear-BA, a binary agreement (BA) that has linear message complexity, constant expected time complexity, and a normal case that has linear communication. We extend Linear-BA to construct Linear-MBA, a multi-valued Byzantine agreement (MBA) protocol also with$O(n)$messages and$O(1)$expected time. Finally, we present Linear-MBA-SV, an MBA protocol with the strong validity property via a no-cost transformation from Linear-MBA. All the protocols above are secure under a static adversary, where a static adversary corrupts a set of replicas at the beginning of the protocol. We go on and show an impossibility result that in the adaptive adversary model (in which the adversary can selectively corrupt the replicas while the protocol is running), one cannot build a Byzantine agreement protocol with$O(n)$messages and$O(1)$expected time. Accordingly, we revise our protocol to obtain Byzantine agreement protocols with$O(n)$messages per round and$O(n)$time. Our results offer a fresh view of what is needed for linear Byzantine agreement: by examining the “needed” assumptions, one can identify the performance bottlenecks for Byzantine agreement. Meanwhile, all our protocols are efficient, as all the building blocks have efficient instantiations.

The second-generation digital video broadcasting via satellite (DVB-S2) and the second-generation DVB interactive satellite system (DVB-RCS2) standards published by European Telecommunications Standards Institute (ETSI) have been dominating the global high-throughput satellite (HTS) communications market for recent five years. ETSI provisioned a technical report (TR) ETSI TR 101 545-4 as rudimentary guidelines for implementing a DVB-S2/DVB-RCS2 satellite system with security functions. Based on the ETSI guidelines, this paper depicts security implementations for a scenario of several distributed hub gateway stations which was unincorporated in the TR. Moreover, several optimizations and modifications were made to improve correctness and efficiency. A top-level star network security architecture, a hub security architecture, a return channel satellite terminal (RCST) security architecture, encrypted frame structures, authentication, and key distribution are described in this paper. The test results shew a less than 9% payload data rate decrease for the given security system in comparison to the unencrypted, proving the same speed performance level as the insecure commercial HTS ground infrastructure.