Paradigm Researcher Proposes PACTs to Protect Bitcoin From Quantum Threats

A Paradigm researcher has outlined a new model designed to protect dormant bitcoins, including those potentially belonging to Bitcoin’s creator Satoshi Nakamoto, from future quantum computing threats. Dan Robinson introduced “Provable Address-Control Timestamps” (PACTs), a proposal that would allow bitcoin holders to prove they controlled a wallet before quantum computing advances to the point of being capable of deriving the wallet’s private keys.

How PACTs Work

The PACTs model uses a timestamping system already built into blockchain functionality. Holders would generate a proof demonstrating they control their bitcoin and timestamp it on the blockchain, creating a record of ownership. This proof could later be unlocked, allowing users to reclaim their funds on a future quantum-resistant version of Bitcoin. The approach aims to solve a major issue in quantum bitcoin defense: protecting the ownership and privacy of long-dormant bitcoin addresses.

Comparison With Alternative Proposals

Other similar proposals, such as BIP-361 by Casa’s chief security officer Jameson Lopp, propose multi-year migration windows for wallets, exchanges, and custodians to upgrade to quantum-resistant technology before “sunsetting” legacy signatures. After that period, any coins that failed to migrate would be rendered unspendable.

However, this approach creates separate problems for dormant holders. Moving funds would reveal that the owner is still active and could potentially link the wallet to others they control. The PACTs model aims to avoid this dilemma by allowing users to prove ownership without broadcasting it onchain.

“This does not require Bitcoin to decide today whether a sunset is necessary,” Robinson wrote, adding that the model gives users a way to prepare early, letting them “plant a seed now” in case protections are needed later.

Quantum Computing Threats to Bitcoin

As quantum computing advances, crypto users and developers must plan for how to defend against potential threats in parallel. Researchers behind BIP-361 warned that more than a third of all bitcoins in circulation could be exposed to quantum attacks due to visible public keys.

Real-world demonstrations are beginning to show incremental progress. Last week, an independent researcher derived a 15-bit elliptic curve key using quantum hardware in what was described as the largest such attack to date, though Bitcoin relies on stronger 256-bit encryption.

Timelines for “Q-Day”—when quantum computers can break modern cryptography—vary depending on who you ask. Google researchers recently suggested a transition to post-quantum cryptography could be needed by around 2029, while others say practical attacks may still be years or decades away.