# LBFT: An Asynchronous Committee-Based Blockchain Storage Strategy on Zero Trust Model
### Our Contributions  
To relieve the storage pressure, two blockchain storage strategies combining erasure coding and BFT protocols, BFT-Store and PartitionChain, have been proposed previously. Based on this idea, we construct LBFT, an improved storage strategy for the public blockchain, which combines Reed-Solomon (RS) coding and the HoneyBadger-BFT (HB-BFT) protocol. Compared to BFT-Store, LBFT has significantly better computational and communication efficiency, and compared to PartitionChain, LBFT trades a small loss of efficiency for greater liveness towards the network situation and node faults. The detailed comparison of the performance is presented in Table 1, where \(t\) is the fixed size of the block partitions in [6] and is usually less than \(\frac{1}{2^{10}}\) of the original block size \(T\). Compared to the previous works, the most significant innovations of the LBFT include the two following aspects:  
* **Completely decentralized:** LBFT is designed on the basis of the conception the zero-trust model, which assumes that all network traffic is untrusted [7; 8]. In LBFT, all the \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **LBFT** & **BFT-Store** & **PartitionChain** \\ \hline Security Model & Zero-Trust Model & Traditional Trust & Traditional Trust \\ Time Assumption & Asynchronous & Partially Synchronous & Partially Synchronous \\ Participants in Dec & Committees & Whole Network & Whole Network \\ Communication & \(O(k^{2}\cdot T+k\cdot c\cdot l)\) & \(O(n^{2}\cdot T+n\cdot l)\) & \(O(n\cdot t+n\cdot l)\) \\ Complexity in Enc & \(O(n\cdot\frac{T^{2}}{c})\) & \(O(n^{2}\cdot T^{2})\) & \(O(n\cdot T\cdot t)\) \\ Complexity in Dec & \(E\cdot O(k\cdot c\cdot T^{2})\) & \(O(n^{3}\cdot T^{2})\) & \(O(n^{2}\cdot T\cdot t)\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The comparison of the performance between LBFT and BFT-Store. messages transmitted on the network are inspected and verified before use by the receivers regardless of previous authority or authentication, which avoids _authentication but not verification_ in the traditional trusted models. Moreover, LBFT deploys a CLAS scheme [9], in which the key generation center only delivers partial private keys in the initialization phase of each party and no longer participates in system operation. * **Committee-based decoding:** In LBFT, only a random part of the nodes divided into several committees participate in the decoding process, to recover the requested data. It can be seen from Table 1 that, in BFT-Store, which requires all the parties to perform decoding, an \(O(n^{2})\) level of communication complexity (where \(n\) is the number of nodes) is incurred, while the communication complexity of LBFT is merely \(O(k\cdot c\cdot l+k^{2}\cdot T)\) (where \(k\) is the number of committees, \(c\) is the number of members in each committee, \(l\) is the decoded message length, and \(T\) is the size of a block). In addition, we aim to make LBFT suitable for more large-scale and complex application scenarios without a pre-set time assumption. We also focus on minimizing the performance loss, including the computational costs, brought by the additional decoding process in comparison with the conventional blockchain system, which adopts the full-replication strategy. More formally, the major advantages and characteristics of LBFT are listed in detail as follows:  
* LBFT is a blockchain storage strategy that obtains higher robustness than BFT-Store and PartitionChain and that is still workable even in scenarios with large geographical ranges and unpredictable network situations. In addition, due to the elimination of a time-bound, the parties will make progress as soon as the messages are delivered, leading to a shorter latency in LBFT. * LBFT is a combination of RS coding and the HB-BFT protocol, which enables each node to store merely a part of encoded blocks rather than a complete ledger in order to decrease storage consumption and improve system scalability.