Paradigm Researcher Proposes PACTs to Shield Bitcoin From Quantum Threats

TLDR:

• PACTs allow Bitcoin holders to timestamp private key ownership off-chain, requiring no transaction or on-chain activity. 
• Satoshi Nakamoto holds over $75 billion in quantum-vulnerable Bitcoin addresses that a CRQC could potentially drain. 
• A STARK proof would let holders reclaim sunsetted funds by proving key knowledge existed before quantum computers arrived. 
• Multisig wallets, custodial setups, and complex scripts still require further standardization before PACTs can cover them.

Provable Address-Control Timestamps (PACTs) are a new scheme proposed by Paradigm researcher Dan Robinson.

The proposal offers Bitcoin holders a way to protect their assets from quantum computing threats. Robinson outlined the concept in a detailed post published on May 1, 2026.

The method allows holders to timestamp proof of key ownership without moving funds on-chain. It addresses a long-standing tension between privacy and security in any future quantum upgrade.

What the PACT Proposal Actually Does

PACTs work by letting holders create a silent, off-chain commitment tied to their private keys. The holder generates a random salt and uses BIP-322 to sign a standardized message proving address control.

That signed message is then hashed into a commitment and timestamped using OpenTimestamps, a free and open-source service.

No Bitcoin transaction is required for this process. OpenTimestamps batches many commitments into a single transaction on the Bitcoin blockchain. This makes the cost of participating effectively zero for individual holders.

Robinson described the Bitcoin network itself as the foundation for this approach, noting that Satoshi Nakamoto had already built the tool needed.

As Robinson wrote, the Bitcoin whitepaper described the network as a “distributed timestamp server,” a function that goes beyond recording transactions.

The commitment reveals nothing about the holder’s address, public key, or wallet balance. Only an opaque hash is published, keeping the entire process private.

Holders must store the salt, the BIP-322 proof, and the OTS file securely, as these become the foundation for any future rescue claim.

The Quantum Sunset Problem and Why It Matters

Bitcoin addresses with exposed public keys are vulnerable to cryptographically relevant quantum computers (CRQCs).

Addresses that have previously sent transactions, thereby revealing their public key, face the greatest risk. Robinson estimates that Satoshi Nakamoto alone holds around 1.1 million BTC in such addresses, worth over $75 billion today.

A “quantum sunset” refers to a potential soft fork that would freeze spending from quantum-vulnerable addresses.

Robinson warned of what inaction could mean, writing that without a sunset, “those holders will be forced to move those coins or let them be stolen.”

The problem is that a sunset forces dormant holders into a difficult position. They must either move their coins publicly, revealing identity and activity, or risk losing access entirely.

Robinson pointed out that “for an early holder like Satoshi, this would be a massive revelation — they would have to tell the world that they are alive and still in possession of their keys.”

PACTs offer a third path. Holders can record their ownership secretly now, then use a zero-knowledge proof later to claim coins under a rescue protocol, if Bitcoin ever adopts one. This separates the act of proving ownership from the act of moving funds publicly.

Rescue Process and Protocol Limitations

If Bitcoin adopts a sunset and a PACT-based rescue path, spending would require a STARK proof. This proof would confirm the holder knew the private key before a defined cutoff date. It would also bind to a specific rescue transaction to prevent replay attacks.

Robinson framed this in practical terms, describing a hypothetical scenario in which Satoshi returns in 2040. He wrote that if Satoshi “had the foresight back in 2026, he could have used a cryptographic timestamping service to timestamp a signature, establishing that he knew the private key before CRQCs existed.”

The salt and BIP-322 proof would never be revealed during a rescue claim. Only the cryptographic proof of their existence would be submitted to the network, maintaining privacy even through the redemption process.

There are real limitations to this approach. Robinson acknowledged that “multisig, complex scripts, custodial wallets, and hardware-wallet support would need careful standardization.”

There is also no guarantee Bitcoin will ever adopt this rescue mechanism, meaning holders should not treat PACTs as a substitute for migrating to quantum-safe addresses once those become available.

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