The activation of ChainLocks on the Dash network has mitigated several additional threat vectors beyond pure 51% attack chain reorganizations.
Originally meant primarily to secure the network against 51% mining attacks where a single actor gains over half of the network hashrate and proceeds to reverse or change transactions, ChainLocks also mitigates other related and less catastrophic issues facing proof-of-work chains as an additional bonus. One such issue is selfish mining, identified by Cornell University researchers Ittay Eyal and Emin Gün Sirer, which consists of miners mining several blocks in secret and then publishing them at once, claiming the rewards for multiple blocks in a row. According to Eyal and Sirer, this is a weakness that affects the decentralization of proof-of-work currencies:
“We show that the Bitcoin mining protocol is not incentive-compatible. We present an attack with which colluding miners obtain a revenue larger than their fair share. This attack can have significant consequences for Bitcoin: Rational miners will prefer to join the selfish miners, and the colluding group will increase in size until it becomes a majority. At this point, the Bitcoin system ceases to be a decentralized currency.”
ChainLocks prevents this centralization vector by locking in the first-seen block and invalidating later-published conflicting blocks, according to Dash Core developer Alexander Block:
“Many attacks based on secret or selfish mining become impossible as they all depend on miners withholding longer and secret chains. Under the current consensus rules, such chains would override the publicly known chain and cause a chain reorganization when published. With ChainLocks however, miners are incentivized to publish every block immediately, even if they in theory have enough hash power to overrule every other miner. Failure to publish creates substantial risks for a malicious miner since any secret chain (even if thousands of blocks longer) would be immediately invalidated if another honest miner publishes a valid block that receives a CLSIG before the secret chain is revealed.”
Essentially, ChainLocks utilize the masternode network to prevent dishonest or undesired actions by miners, allowing the proof-of-work network to operate closer to original intent.
Protections against empty blocks and intermittent network congestion
Another benefit of the recent 0.14 update is the ability to mostly mitigate the threat of an empty block attack. By intentionally mining a block without any transactions, some miners may be able to maximize profits by still collecting the block reward of new coins created without having to field the effort of processing actual transactions, so long as total transaction fees are negligible. In a more malicious situation, a significant miner can exclusively mine empty blocks, losing out on revenue from transaction fees but decreasing the total capacity of the network, allowing it to become congested. This attack may prove ineffective following the most recent Dash upgrade. According to Dash Core CMO Fernando Gutierrez, included in the release of 0.14 in addition to ChainLocks is LLMQ-based InstantSend, which simplifies the instant transaction feature and allows transactions instantly locked to also become instantly respendable:
“Last week Dash activated ChainLocks and LLMQ-Based InstantSend, achieving the finality of transactions that blockchains have promised — in around 1 second. This means that when you send Dash, the recipient receives it in a second and can immediately spend it. The end recipient of any series of these transactions can accept payment without risk or uncertainty that the funds will settle successfully. Dash is now usable exactly as you would expect cash to operate, but within the convenience of the digital world.”
As a side effect of this innovation, empty block attacks are now significantly less effective. If a major portion of the network continues to mine empty blocks, the Dash network continues to operate exactly as it had, with transactions instantly settled and instantly able to be moved again, with a limit of 25 hops before an on-chain confirmation is required. This means that even if transactions are not able to be included in blocks for extended periods of time, they still may be used without issue. As long as the network is not at constant and total capacity, mining a significant portion of empty blocks is not disruptive, and sustained attacks in such an active network can prove costly after lost revenue to transaction fees not gained. This prospect is further mitigated by Dash’s aggressive scaling plan, which research shows can comfortably scale to mass-market levels.
Dash scaling research has found solutions to the poison block propagation attack
In addition to problems solved by ChainLocks, Dash scaling researchers are developing solutions to future attack vectors that may face the network as it grows. One such potential issue is the poison block attack, whereby a miner publishes a block which had not already been broadcast to the network. This essentially has the potential to cancel out block propagation speed improvements such as Xthin and Graphene, causing disruptions to a network under high load. Thankfully, Arizona State University researchers have discovered the Velocity Protocol which maximizes bandwidth efficiency, and believe that when used in conjunction with propagation techniques such as Graphene could counter the poison block attack.
The Dash network currently constitutes one of the most secure and efficient in the world, and further development, research, and innovation promises to attempt to maintain this status moving forward.
Update: This article was updated to clarify that chained InstantSend locks have a limit of 25 hops before an on-chain confirmation is required
