Framework and algorithms for identifying honest blocks in blockchain

Abstract

Blockchain technology gains more and more attention in the past decades and has been applied in many areas. The main bottleneck for the development and application of blockchain is its limited scalability. Blockchain with directed acyclic graph structure (BlockDAG) is proposed in order to alleviate the scalability problem. One of the key technical problems in BlockDAG is the identification of honest blocks which are very important for establishing a stable and invulnerable total order of all the blocks. The stability and security of BlockDAG largely depends on the precision of honest block identification. This paper presents a novel universal framework based on graph theory, called MaxCord, for identifying the honest blocks in BlockDAG. By introducing the concept of discord, the honest block identification is modelled as a generalized maximum independent set problem. Several algorithms are developed, including exact, greedy and iterative filtering algorithms. The extensive comparisons between proposed algorithms and the existing method were conducted on the simulated BlockDAG data to show that the proposed iterative filtering algorithm identifies the honest blocks both efficiently and effectively. The proposed MaxCord framework and algorithms can set the solid foundation for the BlockDAG technology.

Computing the Heaviest Conflict-free Sub-DAG in DAG-based DLTs

“…Analyzing the structure of the DAG to identify the honest blocks has been done by Wang et al [18] and their proposed MaxCord algorithm where honest block identification is modeled as a generalized maximum independent set problem.…”

DAG-Pathwidth: Graph Algorithmic Analyses of DAG-Type Blockchain Networks

“…In this section, we consider a variant of the maximum k-independent set problem for the DAG-type blockchain, which we call the maximum discord k-independent set problem [2]. We design an efficient algorithm for the problem when an input directed graph has a small DAG-pathwidth.…”

“…Such forks occur frequently mainly due to network delay, and many blocks are consequently discarded, which obstructs the enlargement of transaction processing in the blockchain. A promising solution is to make a block point at two or more blocks and then make the blockchain graph form a directed acyclic graph (DAG) [2], which we call a DAG-type blockchain graph (see Fig. 1).…”

“…A DAG-type blockchain requires various combinatorial optimization problems to be solved, such as the decision of reachability of two nodes in a blockchain graph or the computation of the reliability of blocks (note that we do not define the reliability of a block in this paper) [2], [3]. In the reliability computation, we need to solve a variant of the k-independent set problem (see the definition in Sect.…”

“…• We prove that the computation of the DAG-pathwidth of a given graph is NP-complete. • We design a fixed-parameter tractable algorithm for a variant of the maximum k-independent set problem for the DAG-type blockchain, which we call the maximum discord k-independent set problem [2], [3], when the DAG-pathwidth of the input graph is small.…”