Weekly Dev Update January 20th, 2018 — Countdown to the Main Chain

Figure I: The current release of Hcash corresponds to the row marked with bold font.

Our consensus mechanism inherits the merits of Decred[1] and Bitcoin-NG[2], based on which we propose key innovations to make our scheme more secure, efficient and flexible. With the methodology from Bitcoin-NG’s key block/ micro block structure, we offer a two-layer chain structure.

To tackle the security issue existing in Bitcoin-NG, we present two-level mining mechanism to incorporate this into the two-layer chain structure. The level of difficulties for the PoW hash is set and can be adjusted dynamically. When solving the hash, the miner can create a key block once the hard-level difficulty is met. The miner can also publish a micro block, in the case that the low-level difficulty is satisfied. With this the system throughput can be enhanced significantly. The security of the system won’t be compromised because malicious miners cannot spawn massive micro blocks freely.

In order to defend against malicious miners, 51% attacks, and offer the sufficient flexibility we borrowed the idea of Decred’s ticket-voting mechanism. This was combined it with our proposed two-layer chain, which is an efficient and flexible hybrid consensus scheme.

In Hcash, key blocks will be confirmed by certain voting tickets. Both PoW and PoS miners play important roles on the consensus of the system. With this hybrid scheme, we can further implement a basic DAO to provide PoW and PoS miners a mechanism for future protocol updates and project investments. Our scheme supports SegWit, and will allow for lightning network and post-quantum signature schemes. The schematic framework of our consensus scheme is shown in Figure II.

Figure II: The schematic framework of our consensus scheme.

Post-Quantum Features

To address security issues stemming from quantum computers, we designed and implemented post-quantum solutions for Hcash. These implementations need to achieve the following 4 features:

· Compatibility: Compatible with existing ECDSA signature solutions.

· Flexibility: Support multiple post-quantum signature solutions that are thoroughly analyzed, assessed and proven by international cryptography research institutions.

· Security: Post-quantum solution is proven secure in theory, and side-channel attack proven in practice.

· High performance: Signing and signature verification must be fast. Most importantly, the public key and signature must be short.

Hcash is the first blockchain-based system that supports multiple post-quantum signature schemes, and is compatible with the traditional ECDSA signature. We are the first to propose a side-channel-safe implementation of post quantum signature schemes. The block transmission protocol based on SegWit will significantly cut down the communication cost brought by large post-quantum signatures, and this protocol can be generalized and transplanted into other blockchain systems.[3]

Where We Are Today

Unit testing and functional testing (in progress till 1/22/18)

o Deployed private test net with 20 nodes and 20 miners.

o Testing Priority 1: In all cases where “address”, “public key” or “private key” are used as inputs, run a separate case for both default addresses/ keys and post-quantum addresses/ keys and manually verify results for post-quantum signature scheme.

§ Modify and create scripts as needed to test and verify each function on https://github.com/HcashOrg/hcashd.

§ Ensure test scripts properly test relevant functions.

§ Find functions that do not have tests written, specifically new functions for Bitcoin-NG and the post-quantum signature scheme.

§ Ensure proper testing for post-quantum address/ key/ signature generation/ verification.

Where We Plan To Be Next Week

Load/ Volume testing to begin and continue till the end of February. This involves:

o Applying heavy loads of node traffic and transactions to test stability of post-quantum signature scheme, NG protocol, node implementations and node peer network.

o Attempts to overload mempool and micro/ key blocks, spamming high volume requests for data to nodes and DDoS like requests from the node peer network.

o Apply all tests in a sustained fashion for stress testing.

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[1] Jepson, Christina. DTB001: Decred Technical Brief. 20 Dec. 2015, coss.io/documents/white-papers/decred.pdf.

[2] Eyal, Ittay, et al. “Bitcoin-NG: A Scalable Blockchain Protocol.” Bitcoin-NG: A Scalable Blockchain Protocol, 16 Mar. 2015, pp. 45–59., www.usenix.org/system/files/conference/nsdi16/nsdi16-paper-eyal.pdf.

[3]LoCCS Shanghai Jiao Tong University, HcashOrg. “HcashOrg/Hcashd.” GitHub, 19 Jan. 2018, github.com/HcashOrg/hcashd.

“BLISS: Bimodal Lattice Signature Schemes.” BLISS Signature Scheme, bliss.di.ens.fr.



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