A Bloom-filter-based Unique Address Checking Approach for DAG-based Blockchain Systems

Winternitz One-Time Signature (WOTS) is a quantum-resistant signature mechanism that has been widely used in DAG-based blockchain systems. However, it needs to generate a unique private/public key pair for each transaction, which severely limits blockchain performance by performing a time-consuming unique address checking process when generating transactions. This paper proposes a bloom-filter-based approach, called ABACUS, to optimize the unique address checking process in WOTS. In ABACUS, we separate the large address space into multiple small subspaces and apply bloom filters to perform uniqueness checking for all addresses in one subspace. Specifically, we propose a two-level address space mechanism to strike a balance between the checking efficiency and the memory/storage space overhead of the bloom filter design. A bucket-based scalable bloom filter design is proposed to match the growth of used addresses with efficient I/O access by storing all sub-bloom-filters together in one bucket. To further reduce disk I/Os, ABACUS incorporates an in-memory write buffer and a read-only cache. To reclaim wasted addresses, we also propose a layered address recycling mechanism by efficiently checking and reusing unused addresses that were identified as used due to false positives of bloom filters. We have implemented a fully functional prototype of ABACUS and integrated it into IOTA, a widely-used DAG-based blockchain system. A series of experiments have been conducted on a private IOTA system. Experimental results show that ABACUS can significantly reduce the transaction generation time by up to four orders of magnitude, and achieve up to 3X boost on the system throughput with more than 80% space-saving. We have released the open-source code of ABACUS for public access.