Paradigm Researcher Proposes PACT Model to Protect Bitcoin From Quantum Threats

A Paradigm researcher has outlined a new model designed to protect dormant bitcoins, including those belonging to Bitcoin’s creator Satoshi Nakamoto, from potential quantum computing threats. Dan Robinson introduced what he calls “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 deriving private keys, according to Paradigm’s research.

How PACTs Work

The PACT model leverages timestamping systems already built into blockchain functionality. Holders would generate a proof demonstrating they control their bitcoin and timestamp it on the blockchain, creating an ownership record in the event of a future quantum attack. This proof could later be unlocked, allowing users to reclaim their funds on a future quantum-resistant version of Bitcoin.

Robinson’s proposal addresses a major challenge in quantum bitcoin security: protecting ownership and privacy of long-dormant bitcoin addresses. Under alternative proposals like BIP-361, developed by Casa’s chief security officer Jameson Lopp, there would be a multi-year migration window 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 become unspendable.

However, this creates a separate problem for dormant holders. Moving funds would reveal that the owner is still active and could potentially link the wallet to other addresses they control. The PACT 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, according to the proposal. He noted the model gives users a way to prepare early, letting them “plant a seed now” in case protections are needed later.

Quantum Computing Threats and Timelines

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 one-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. An independent researcher recently 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 the source. 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.