Will Quantum Advances Threaten Bitcoin’s Forgotten Stashes?

Concerns are mounting over Bitcoin‘s potential vulnerability to future quantum computing capabilities, particularly concerning dormant coins. The spotlight is on an estimated 1.1 million Bitcoins—valued today at nearly $84 billion—believed to be linked to Bitcoin creator, Satoshi Nakamoto. Experts caution that if quantum computers become powerful enough, these machines might potentially decode private keys of these historical addresses, enabling unauthorized transfers.

Can BIP-361 Provide a Safety Net?

To mitigate this looming threat, one prominent strategy involves implementing a soft fork to prevent transactions from vulnerable old addresses on the Bitcoin network. This approach would mean compelling legacy Bitcoin holders to move their holdings to quantum-resistant wallets. In a bid to facilitate this, Bitcoin developer Jameson Lopp and his team proposed BIP-361—a framework aiming to push this transition within five years, ultimately freezing coins left untransferred.

The initiative does, however, pose an intricate quandary as it affects dormant addresses potentially owned by unidentified entities, including Satoshi Nakamoto, raising privacy and identity issues.

Dan Robinson of Paradigm investment firm observed that current proposals either undermine security against quantum attacks or risk violating the property rights of dormant address owners.

How Do PACTs Align with Privacy?

In response, Dan Robinson introduced Provable Address-Control Timestamps (PACTs) as a solution. PACTs afford an address owner the ability to verify control over a wallet at a certain time without publicizing sensitive data or spending coins.

This method involves generating a secret salt along with a proof of ownership aligned with the BIP-322 standard, which allows address signing without moving coins. These elements are secured on the blockchain using OpenTimestamps, maintaining the confidentiality of salt and proof files compared to the proposal exemplified by BIP-361.

In case the network chooses to freeze legacy addresses, users could deploy a STARK-based zero-knowledge proof to retrieve their holdings. STARK technology is considered to be resistant to quantum-based threats, reinforcing its potential as a protective measure.

Can BIP-32 and Bitcoin’s Framework Support This Innovation?

This approach is particularly useful for BIP-32 deterministic wallets, initiated in 2012. However, many of Satoshi Nakamoto’s original addresses predate this standard, and might not benefit from these safeguards. Robinson highlighted that integrating STARK verification into Bitcoin’s core would necessitate another soft fork and substantial community backing.

Furthermore, comprehensive system improvements would be needed, especially with multi-signature setups, intricate smart contracts, and hardware wallet integration. Should Satoshi or the key holders remain absent, the choices narrow down to freezing these coins or risking a future quantum breach.

PACTs offer an innovative alternative in the ongoing discourse on legacy Bitcoin addresses, though there’s no definitive indication that individuals like Satoshi will ever resort to this recourse.