Ex-Meta engineer flags 2 existential threats to Bitcoin's security model

A former Meta engineer published a warning on July 11 identifying quantum computing's cryptographic risk and declining miner block rewards as two existential threats to Bitcoin's long-term security.

Bitcoin faces a dual threat from quantum computing and its own incentive structure, a former Meta engineer warned, as Google research suggests encryption-breaking machines could arrive by 2029.

"The combination of cryptographic vulnerability and shrinking miner compensation creates a structural risk the network has never faced simultaneously," the engineer said in the analysis, which was circulated among industry security researchers.

Roughly 35% to 50% of Bitcoin's circulating supply could be exposed to a quantum computing attack, according to an unpublished June 2026 working paper by independent researcher Ahmed Raza Muhammad Umer. That represents about 6.9 million BTC in legacy wallets or reused addresses where public keys have already been exposed on-chain, per estimates cited by BitGo. Declining block rewards — which halve approximately every four years — reduce the financial incentive for miners to maintain network security, potentially making the chain more susceptible to reorganization attacks.

The warning adds pressure on Bitcoin developers to agree on a post-quantum upgrade path, a process stalled by disagreements over which cryptographic standard to adopt. None of the top 20 blockchains have deployed a post-quantum signature algorithm, executives said, and the Ethereum Foundation is targeting 2029 for full quantum protection.

Quantum Timeline Compresses as Google Sets 2029 Target

Google's Quantum AI team published a March 2026 whitepaper suggesting that breaking Bitcoin's elliptic curve cryptography could require fewer than 500,000 physical qubits, a threshold the company believes could be reached by 2029. The finding compressed what many in the industry had assumed was a 10-to-20-year timeline. Blockstream CEO Adam Back maintains the existential quantum threat is still 20 to 40 years out, but BitGo CEO Mike Belshe has warned that "the safest key is one whose public key has never been revealed on-chain."

BitGo launched quantum-risk tools on July 9 that help institutional Bitcoin holders identify and reduce potential future quantum-computing exposure in their custody wallets. The tools allow clients to scan for addresses with exposed public keys and move funds to quantum-safe storage. U.S. President Donald Trump last month issued executive orders to bolster U.S. quantum capability, acknowledging the risks the technology poses to both public and private sectors.

Miner Economics Add a Second Layer of Risk

The engineer's second concern centers on Bitcoin's security model, which relies on miners expending computational power to validate transactions. Each halving cuts the block reward in half — the most recent reduction in April 2024 lowered it to 3.125 BTC per block. As rewards shrink, miners with higher operating costs may exit the network, reducing hash rate and making the chain cheaper to attack. Transaction fees have not yet risen enough to fully replace block rewards as miner compensation, creating what the engineer described as a "revenue gap" that could widen over successive halving cycles.

Christopher Wood, global head of equity strategy at Jefferies, removed a 10% bitcoin allocation from his model portfolio in January due to the long-term "existential" threat of quantum computing, he wrote in his January newsletter. The Jefferies move shows that institutional investors are beginning to price in quantum risk, even if the timeline remains uncertain. Chris Tam, head of quantum innovation at BTQ Technologies, described quantum computing as "the most direct and existential threat towards cryptocurrencies and crypto networks."

This article is for informational purposes only and does not constitute investment advice.