Paradigm researcher proposes PACTs to protect dormant bitcoin

Dan Robinson, a researcher at Paradigm, proposed Provable Address‑Control Timestamps (PACTs) to let holders of dormant bitcoin addresses create a timestamped proof that they controlled an address at a given time. The proof would sit on the blockchain without revealing ownership until it is needed.

Under PACTs, an owner would generate a cryptographic proof tied to a specific address and commit a timestamp of that proof onchain. The timestamped commitment creates a verifiable record that control existed at the time of the commit but does not immediately disclose the owner or move funds.

If quantum computers later make it possible to derive private keys from public data, the holder could reveal the preexisting proof and use it to reclaim funds on a migrated, quantum‑resistant chain or an upgraded protocol. Robinson characterizes the design as preparatory rather than a change that must be applied to Bitcoin today.

The proposal responds to planning for a potential transition to post‑quantum cryptography. Some migration plans call for a multi‑year window during which wallets, exchanges and custodians would switch to quantum‑resistant keys and legacy signatures would be sunsetted. Moving funds during a migration would show an address is still controlled and could link it to other wallets; PACTs aim to let owners record proof without revealing active control.

PACTs rely on existing blockchain features for timestamping commitments and do not, by themselves, alter Bitcoin’s signature scheme. Robinson described the idea as a way for holders to “plant a seed now” and added, “This does not require Bitcoin to decide today whether a sunset is necessary.”

Bitcoin uses elliptic‑curve signatures (secp256k1) for transaction authorization. Researchers have demonstrated incremental progress in using quantum hardware against elliptic‑curve keys, including an experiment that derived a 15‑bit elliptic‑curve key. Current Bitcoin keys use 256‑bit elliptic‑curve cryptography. Estimates for when quantum computers could break modern cryptography vary; some researchers have suggested a transition to post‑quantum algorithms may be needed by about 2029, while others expect practical quantum attacks to remain years or decades away.

PACTs are a proposal rather than a standard or imminent protocol change. Robinson presents them as an option for individual holders to prepare for a future cryptographic threat while avoiding immediate disclosure of address control.