Time is Running Out for Bitcoin to Mitigate Quantum Computing Threat

Not all aspects of bitcoin are vulnerable to quantum computers. The process of bitcoin mining, which utilizes a type of mathematics known as hashing, is resistant to quantum attacks. The blockchain itself and the rule that new bitcoins can only be created through mining would remain intact in the event of a quantum attack. However, ownership of bitcoins would be at risk. Bitcoin wallets rely on a different type of mathematics that converts a private key into a public address. This math is easily reversible in one direction but not the other, which is the primary obstacle preventing unauthorized individuals from spending someone else's coins. A quantum algorithm known as Shor's algorithm can bypass this obstacle. Google's recent paper demonstrated that this attack could be executed with significantly fewer resources than previously estimated, and within a timeframe that competes with bitcoin's block times. This article, the final installment of a series, focuses on the response to this threat. It examines what is at risk, the measures bitcoin has taken to address the issue, and whether a network designed to resist coordinated change can implement the most significant security upgrade in its history before quantum hardware becomes a reality. The pool of vulnerable bitcoin is substantial, with roughly 6.9 million coins, approximately one-third of all mined bitcoin, stored in wallets whose public keys are permanently visible on the blockchain. This includes early bitcoin from the network's first years, which was stored in an address format that published the public key by default, as well as any wallet that has ever been spent from, as spending reveals the key for any remaining balance. A quantum attacker would not need to compete with an ongoing transaction; instead, they could systematically target wallets with exposed keys at their own pace. Bitcoin's pseudonymous creator, Satoshi Nakamoto, holds approximately 1 million bitcoin, which has remained untouched since the network's early days and now falls into the exposed category. The 2021 Taproot upgrade inadvertently expanded the problem. Taproot is a modification to how bitcoin addresses function, intended to make transactions more efficient and private. However, it had the side effect of publishing the key that protects any remaining balance at an address after a transaction has been made. While this was not an error, it was a reasonable trade-off at the time, given the perceived timeline for quantum threats. Currently, there are no concrete plans from Bitcoin developers to address the quantum threat. In contrast, Ethereum, a major competitor, has had a formal quantum-resistant program in place since 2018. The Ethereum Foundation operates four full-time teams working on the migration and has multiple independent developer groups releasing weekly test networks. Ethereum has outlined specific upgrades across four upcoming network-wide changes, aiming to transition its security to quantum-resistant mathematics. It has also launched a dedicated website to track its progress. Bitcoin lacks a comparable strategy. There are, however, efforts underway to solve the problem. One formal proposal, BIP-360, suggests introducing new quantum-safe address types that holders could voluntarily migrate to. Another proposal from BitMEX Research recommends implementing a detection system that would trigger defensive actions if a quantum attack is observed on the network. Neither proposal has garnered broad support from bitcoin's core developers, and they address different aspects of the problem. Prominent bitcoin advocate Nic Carter has voiced concerns, stating that the elliptic curve cryptography used by bitcoin is on the verge of becoming obsolete. He praised Ethereum's approach as 'best in class' and criticized bitcoin's as 'worst in class,' citing developers who deny or downplay the issue rather than engaging with it. Adam Back, CEO of Blockstream and an early bitcoin contributor, disagrees on the urgency but agrees that bitcoin should prepare by integrating optional upgrades in advance, allowing the network to migrate when necessary rather than reacting in crisis mode. The biggest challenge in implementing effective solutions against the quantum threat is coordination. Bitcoin's migration is more complex than Ethereum's due to reasons unrelated to the mathematics involved. Ethereum has a foundation that funds engineering work and a governance process that regularly implements major upgrades. Bitcoin, on the other hand, lacks a central authority and treats any such entity as a failure mode, with a development culture that views changes to the protocol as rare and difficult. These principles have maintained the network's stability for nearly two decades but make addressing the quantum problem structurally more challenging for bitcoin. Migrating the 6.9 million exposed coins requires decisions that the network has avoided for twenty years. Questions arise about whether old address formats should be frozen after a certain date to protect coins from future theft, whether exposed coins should be allowed to move to new quantum-safe addresses using their original keys, and what happens to coins whose owners cannot or will not migrate. Satoshi's coins are a prime example, as freezing old formats protects the coins but makes them permanently inaccessible, including to Satoshi, while leaving the old formats open means those coins are vulnerable to quantum attacks. Setting a migration deadline would force Satoshi to either move the coins, revealing ownership, or lose them. Every option changes bitcoin's character in ways the network has historically refused to change. The Google paper's framing serves as a summary of the industry's current stance. A successful attack on bitcoin's mathematics 'should not be seen as a wake-up call to adopt post-quantum cryptography as much as a potential signal that PQC adoption has already failed.' This implies that by the time the threat becomes apparent, the window to respond may already have closed. Developers are now faced with the question of whether a network built to resist coordinated change can coordinate the largest security upgrade in its history before quantum hardware catches up. Ethereum's eight-year head start suggests that starting now is the correct approach, while bitcoin's governance culture indicates a likelihood of waiting until the threat is demonstrated before taking action. Only one of these approaches will be effective if the timeline proves shorter than estimated.