Monero’s Response to Recent Hashrate Disruption
Recent developments in the Monero (XMR) network have prompted developers and pool operators to consider a rapid software-level response to last week’s hashrate anomaly. The Qubic mining pool claimed to have briefly dominated the network, leading to a six-block reorganization. Riccardo Spagni, the former lead maintainer of Monero, has proposed a strategy known as “detective mining” to counteract selfish-mining attacks without needing a hard fork. Spagni outlined this proposal in a new Monero Research Lab issue, emphasizing that it could make Monero resilient to such attacks without altering the protocol.
Qubic’s Mining Tactics and Industry Response
On August 12, Qubic made public statements claiming it had surpassed 51% of Monero’s hashrate and successfully reorganized the blockchain. This event was part of what Qubic called a live “51% takeover demo.” The method employed, described as “selfish mining,” can yield disproportionate rewards with as little as 33-40% of the network’s hashrate, not necessarily requiring a full majority.
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In response, risk controls were activated across the industry. For instance, Kraken issued a status notice in mid-August, pausing XMR deposits after detecting that a single mining pool had gained more than 50% of the network’s total hashing power. While this pause was in effect, trading and withdrawals remained open as the network’s integrity was closely monitored. The incident highlighted how even brief reorganizations could compel exchanges to reevaluate their confirmation policies.
Analysis of Qubic’s Claims
Not everyone agreed with Qubic’s portrayal of the situation. Analysts at the RIAT Institute argued that no genuine 51% attack had occurred, citing data indicating that Qubic’s peak influence was significantly less than a true majority. They also noted that a six-block reorganization is insufficient proof of sustained control capable of reversing confirmed transactions.
Detective Mining: A Defensive Strategy for Monero
Spagni’s “detective mining” strategy aims to eliminate the advantage any pool attempting selfish mining might have by using information already available in pool job messages. In pooled mining, Stratum job payloads include the previous block hash (“prevhash”). A detective miner, or a pool running a “sensor” proxy, can subscribe to competing pools’ job streams. If a leaked prevhash does not match the public tip, the pool can immediately build and broadcast a valid child block on top of the attacker’s hidden parent block, forcing the selfish miner to either reveal or lose its private lead. This strategy operates entirely at the pool/Stratum-proxy layer and requires no consensus or protocol changes, making it deployable on Monero’s current infrastructure.
The Economic Implications
The economic impact is crucial. According to Spagni’s summary of the Lee–Kim model (2019), if approximately half of the network’s hashrate (the largest pools) adopt detective mining, the selfish miner’s break-even threshold increases to around 32–42%, depending on tie-breaking assumptions. This significantly diminishes the profitability of such attacks and, with broader adoption, could eliminate them entirely. This threshold is notably higher than the classical Eyal–Sirer result, where selfish mining could be profitable with just one-quarter to one-third of the hashrate.
Anticipating Adversarial Responses
Spagni’s proposal also considers potential adversarial counter-moves. It suggests using quorum-based detection from multiple sensors, short “grace windows” before redirecting hashrate, and share-submission checks to counter decoy jobs. All these measures are complemented by rate limits and telemetry to manage false-positive risks. These are pragmatic playbooks for pool operators rather than protocol-level rules, aligning with Monero’s approach of strengthening incentives and operations before making consensus changes.
Future Directions for Monero
For Monero, the next steps will be as much social as they are technical. Major mining pools would need to implement and enable detective mining logic for the defense to be effective at the projected thresholds. As of August 19, the idea remains a public proposal under active discussion rather than an established standard. However, in the wake of a single pool’s campaign that led to a noticeable reorganization and necessitated exchange-level mitigations, updating pool software to increase the cost of selfish mining has emerged as the logical short-term response for the project.
At the current time, XMR is trading at $268.
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