BTQ’s Bitcoin Quantum Testnet and “Old BTC” Risk, Explained

Key takeaways

• Bitcoin’s quantum danger facilities on uncovered public keys and signature safety.

• BTQ’s testnet explores post-quantum signatures in a Bitcoin-like atmosphere.

• Publish-quantum signatures considerably enhance transaction measurement and block area calls for.

• “Outdated BTC danger” is concentrated in legacy output sorts and tackle reuse patterns.

BTQ Applied sciences stated it had launched a Bitcoin Quantum testnet on Jan. 12, 2026, a Bitcoin-like community designed to trial post-quantum signatures with out touching Bitcoin mainnet governance.

The thought is that BTQ would substitute Bitcoin’s current signature scheme with ML-DSA, the module-lattice signature commonplace formalized by the Nationwide Institute of Requirements and Expertise (NIST) as Federal Info Processing Customary (FIPS) 204, for post-quantum safety assumptions.

It’s price remembering that in most Bitcoin quantum-threat models, the important thing precondition is public-key publicity. If a public secret’s already seen onchain, a sufficiently succesful future quantum laptop may, in concept, try and get better the corresponding non-public key offline.

Do you know? BTQ Applied sciences is a research-focused agency engaged on post-quantum cryptography and blockchain safety. Its Bitcoin Quantum testnet is designed to review how quantum-resistant signatures behave in a Bitcoin-like system.

What quantum adjustments?

Most Bitcoin quantum-risk discussions deal with digital signatures, not on Bitcoin’s coin provide or the concept a quantum laptop may magically guess random wallets.

The precise concern is {that a} cryptographically related quantum laptop (CRQC) may run Shor’s algorithm to unravel the discrete logarithm downside effectively sufficient to derive a personal key from a identified public key, undermining each the Elliptic Curve Digital Signature Algorithm (ECDSA) and Schnorr-based signing.

Chaincode Labs frames this because the dominant quantum risk mannequin for Bitcoin as a result of it may allow unauthorized spending by producing legitimate signatures.

The danger might be separated into long-range publicity, the place public keys are already seen onchain for some older script sorts or resulting from reuse, and short-range publicity, the place public keys are revealed when a transaction is broadcast and awaits affirmation, making a slender time window.

After all, no quantum laptop right this moment poses an instantaneous danger to Bitcoin, and mining-related impacts must be handled as a separate and extra constrained dialogue in contrast with signature breakage.

Do you know? Shor’s algorithm already exists as arithmetic, but it surely requires a big, fault-tolerant quantum laptop to run. If such machines are constructed, they could possibly be used to derive non-public keys from uncovered public keys.

What BTQ constructed and why it’s attention-grabbing

BTQ’s Bitcoin Quantum testnet is basically a Bitcoin Core-based fork that swaps out one in every of Bitcoin’s most vital primitives, signatures.

In its announcement, BTQ stated the testnet replaces ECDSA with ML-DSA, the module-lattice signature scheme standardized by the NIST as FIPS 204 for post-quantum digital signatures.

This alteration forces a set of engineering trade-offs. ML-DSA signatures are roughly 38-72 occasions bigger than ECDSA, so the testnet raises the block measurement restrict to 64 mebibytes (MiB) to make room for the extra transaction information.

The corporate additionally treats the community as a full lifecycle proving floor, supporting wallet creation, transaction signing and verification, and mining, together with fundamental infrastructure similar to a block explorer and mining pool.

Briefly, the testnet’s sensible worth is that it turns post-quantum Bitcoin right into a efficiency and coordination experiment.

The place previous BTC danger concentrates

When analysts talk about “previous BTC danger” in a post-quantum context, they’re normally referring to public keys which are already uncovered onchain.

A future CRQC able to working Shor’s algorithm may, in concept, use these public keys to derive the corresponding non-public keys after which produce legitimate spends.

There are three output sorts instantly susceptible to long-range assaults, particularly as a result of they place elliptic-curve public keys instantly within the locking script (ScriptPubKey): Pay-to-Public-Key (P2PK), Pay-to-Multi-Signature (P2MS) and Pay-to-Taproot (P2TR).

The distribution is uneven:

• P2PK is a tiny share of right this moment’s unspent transaction outputs (UTXOs), round 0.025%, but it surely locks a disproportionate share of BTC worth, about 8.68% or 1,720,747 Bitcoin (BTC), principally dormant Satoshi-era cash.

• P2MS accounts for about 1.037% of UTXOs, however studies estimate that it secures solely round 57 BTC.

• P2TR is widespread by rely, round 32.5% of UTXOs, but small by worth in the identical snapshot, about 0.74% or 146,715 BTC. Its publicity is tied to Taproot’s key-path design, the place a tweaked public secret’s seen onchain.

Deal with reuse can even flip what would in any other case be “spend-time” publicity into long-range publicity as a result of as soon as a public key seems onchain, it stays seen.

BTQ’s personal messaging makes use of this exposed-key framing to argue that the doubtless affected pool is massive. It cites 6.26 million BTC as uncovered, which is a part of why the corporate says testing post-quantum signatures in a Bitcoin-like atmosphere is price doing now.

What’s subsequent for Bitcoin?

Within the close to time period, essentially the most concrete work is observability and preparedness.

As explored, the signature risk mannequin is pushed by public-key publicity. For this reason discussions typically heart on how Bitcoin’s current pockets and scripting practices both reveal public keys early, as with some legacy script sorts, or cut back publicity by default, as with widespread pockets habits that avoids reuse.

“Outdated BTC danger” is subsequently largely a property of historic output sorts and reuse patterns and never one thing that abruptly applies evenly to every coin.

The second, extra sensible constraint is capability. Even when a post-quantum migration have been socially agreed upon, it could nonetheless be a blockspace and coordination downside.

River’s explainer summarizes tutorial estimates exhibiting how delicate timelines are to assumptions. A theoretical situation wherein all transactions are migrations can compress timelines dramatically, whereas extra lifelike blockspace allocation stretches a transition into years, even earlier than accounting for governance and adoption.

BTQ’s testnet suits into that bucket. It lets engineers observe the operational prices of post-quantum signatures, together with bigger information sizes and completely different limits, in a Bitcoin-like setting, with out claiming that Bitcoin is imminently breakable.

Do you know? The most important issue holding quantum computer systems again is noise, or errors. Right this moment’s qubits make errors regularly, so fault-tolerant error correction is required. This implies utilizing many bodily qubits to supply a small variety of dependable “logical” qubits earlier than working the lengthy computations wanted to interrupt real-world cryptography.

What Bitcoin-level mitigation would possibly appear like

On the protocol degree, quantum preparedness is usually mentioned as a sequenced path.

Publish-quantum signature schemes are usually a lot bigger than elliptic-curve signatures, which have knock-on results for transaction measurement, bandwidth and verification prices; the identical sorts of trade-offs BTQ is surfacing by experimenting with ML-DSA.

That’s the reason some Bitcoin proposals focus first on decreasing essentially the most structural publicity inside current script designs, with out committing the community to a particular post-quantum signature algorithm instantly.

A latest instance is Bitcoin Enchancment Proposal (BIP) 360, which proposes a brand new output kind referred to as Pay-to-Tapscript-Hash (P2TSH). P2TSH is sort of equivalent to Taproot however removes the key-path spend, the trail that depends on elliptic-curve signatures, leaving a tapscript-native route that can be utilized in methods meant to keep away from that key-path dependency.

Associated concepts have circulated on the Bitcoin developer mailing listing beneath the broader “hash-only” or “script-spend” Taproot household, typically mentioned as Pay-to-Quantum-Resistant-Hash (P2QRH)-style constructions. These proposals once more intention to reuse Taproot’s construction whereas skipping the quantum-vulnerable key spend.

Importantly, none of that is settled. The principle level is that Bitcoin’s possible response, if it strikes, is debated as an incremental coordination downside that balances conservatism, compatibility and the price of altering the transaction format.

The BTQ testnet is kind of revealing

BTQ’s Bitcoin Quantum testnet doesn’t settle the quantum debate, but it surely does make two factors tougher to disregard.

First, most credible risk fashions deal with the place public keys are already uncovered, which is why “previous coin” patterns maintain showing in analyses.

Second, post-quantum Bitcoin is an engineering and coordination downside. BTQ Applied sciences’ personal design selections, similar to transferring to ML-DSA and lifting block limits to accommodate a lot bigger signatures, illustrate these trade-offs.

Finally, the testnet is a sandbox for measuring prices and constraints and shouldn’t be seen as proof that Bitcoin is imminently breakable.