A new report from the International Association for Cryptologic Research (IACR) has claimed Bitcoin Unlimited’s (BU) security promises are “invalid.”

The paper, elaborately titled ‘On the Necessity of a Prescribed Block Validity Consensus: Analyzing Bitcoin Unlimited Mining Protocol,’ states that BU’s two central tenets of security are incompatible with the needs of a cryptocurrency network.

“[...W]e systematically evaluate BU's security with three incentive models via testing the two major arguments of BU supporters: the block validity consensus [BVC] is not necessary for BU's security; such consensus would emerge in BU on the run,” its abstract begins.

“Our results invalidate both arguments and therefore disprove BU's security claims.”

While BU has yet to respond, if the findings gain wider acceptance they would deal a further blow to Roger Ver and other proponents of ‘big blocks,’ the introduction of which has been the source of argument throughout the industry for several years.

Meanwhile continuing the announcement, the IACR also concluded by demonstrating the need for miners to accept a BVC.

“Our further analysis shows that at the core of the newly introduced attack vectors is BU’s abandonment of a prescribed BVC,” it states.

“Based on this conclusion, we propose a countermeasure to BU’s vulnerabilities, which allows miners to collectively decide the block size limit without abandoning prescribed BVC.”

Ver’s Bitcoin.com had since joined the list of mining pools to signal for BIP 91, a method of SegWit activation which would not require a mandatory hard fork for Bitcoin. Most recent feedback, however, shows the pool returning to BU signaling.