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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 surroundings.

• Put up-quantum signatures considerably improve transaction dimension and block house 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• “Outdated BTC danger” is concentrated in legacy output sorts and tackle reuse patterns.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 exchange Bitcoin’s present signature scheme with ML-DSA, the module-lattice signature customary formalized by the Nationwide Institute of Requirements and Expertise (NIST) as Federal Data Processing Commonplace (FIPS) 204, for post-quantum safety assumptions.

It’s price remembering that in most Bitcoin quantum-threat fashions, the important thing precondition is public-key publicity. If a public secret is already seen onchain, a sufficiently succesful future quantum laptop might, in idea, try to 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 concentrate on digital signatures, not on Bitcoin’s coin provide or the concept a quantum laptop might magically guess random wallets.

The particular concern is {that a} cryptographically related quantum laptop (CRQC) might run Shor’s algorithm to resolve the discrete logarithm drawback effectively sufficient to derive a non-public 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 might allow unauthorized spending by producing legitimate signatures.

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

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

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

What BTQ constructed and why it’s fascinating

BTQ’s Bitcoin Quantum testnet is actually a Bitcoin Core-based fork that swaps out one in all 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 modification forces a set of engineering trade-offs. ML-DSA signatures are roughly 38-72 occasions bigger than ECDSA, so the testnet raises the block dimension restrict to 64 mebibytes (MiB) to make room for the extra transaction knowledge.

The corporate additionally treats the community as a full lifecycle proving floor, supporting pockets creation, transaction signing and verification, and mining, together with primary infrastructure reminiscent of a block explorer and mining pool.

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

The place outdated BTC danger concentrates

When analysts discuss about “outdated BTC danger” in a post-quantum context, they’re normally referring to public keys which might be already uncovered onchain.

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

There are three output sorts instantly weak to long-range assaults, particularly as a result of they place elliptic-curve public keys straight 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 now’s unspent transaction outputs (UTXOs), round 0.025%, however it 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 is 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 possibly affected pool is giant. 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 surroundings is price doing now.

What’s subsequent for Bitcoin?

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

As explored, the signature risk mannequin is pushed by public-key publicity. This is the reason discussions usually 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 conduct that avoids reuse.

“Outdated BTC danger” is due to this fact largely a property of historic output sorts and reuse patterns and never one thing that all of the sudden applies evenly to each coin.

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

River’s explainer summarizes educational estimates exhibiting how delicate timelines are to assumptions. A theoretical situation by which all transactions are migrations can compress timelines dramatically, whereas extra sensible 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 knowledge sizes and totally 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. At the moment’s qubits make errors ceaselessly, so fault-tolerant error correction is required. This implies utilizing many bodily qubits to provide a small variety of dependable “logical” qubits earlier than operating the lengthy computations wanted to interrupt real-world cryptography.

What Bitcoin-level mitigation may appear to be

On the protocol stage, quantum preparedness is commonly mentioned as a sequenced path.

Put up-quantum signature schemes are usually a lot bigger than elliptic-curve signatures, which have knock-on results for transaction dimension, 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 probably 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 sort 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 supposed to keep away from that key-path dependency.

Associated concepts have circulated on the Bitcoin developer mailing checklist below the broader “hash-only” or “script-spend” Taproot household, usually mentioned as Pay-to-Quantum-Resistant-Hash (P2QRH)-style constructions. These proposals once more purpose 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 drawback that balances conservatism, compatibility and the price of altering the transaction format.

The BTQ testnet is sort of revealing

BTQ’s Bitcoin Quantum testnet doesn’t settle the quantum debate, however it does make two factors more durable to disregard.

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

Second, post-quantum Bitcoin is an engineering and coordination drawback. BTQ Applied sciences’ personal design decisions, reminiscent of shifting 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.