- Quantum advances may shorten Bitcoin’s timeline for future signature attack risks.
- Lost Bitcoin wallets may face quantum risk because owners cannot migrate exposed funds.
- BitGo tested post-quantum custody tools as firms review Bitcoin migration options.
Bitcoin’s quantum risk is moving from theory into a practical migration debate. Quantus warned that recent progress in quantum hardware and error correction could shorten the timeline for attacks against blockchain signature systems.
According to “The State of Quantum” from Quantus, recent advances from Google, IBM and Quantinuum have changed expectations around cryptographically relevant quantum computers. The report said the mathematical path to breaking elliptic curve cryptography has been understood for decades.
Quantum Advances Raise Bitcoin Security Concerns
Bitcoin relies on secp256k1 elliptic curve cryptography to secure private keys and transactions. Quantus said no current machine could break Bitcoin’s cryptography, but it argued that estimated resource requirements have fallen sharply.
The report cited Google Quantum AI’s March 2026 paper as a major development. According to Quantus, the paper estimated that Shor’s algorithm could break secp256k1 with fewer than 500,000 physical qubits under certain hardware assumptions.
Quantus said three research papers released within roughly one year reduced projected quantum resources for attacking elliptic curve cryptography by nearly an order of magnitude.
The report said cryptocurrencies face a harder transition than centralized internet companies. Centralized services could update encryption standards through controlled software changes. While public blockchains expose transaction history and public keys on open ledgers.
Quantus described this as a “harvest now, crack later” risk. Attackers could store exposed blockchain records now and target vulnerable public keys later with stronger quantum systems.
The concern is broader than old wallets.
Unconfirmed BTC transactions could reveal public keys before settlement, creating a possible attack window if a quantum computer could derive a private key before a block is confirmed.
Older Bitcoin address formats carry higher exposure. P2PK addresses reveal public keys permanently on-chain. While newer formats such as P2PKH and P2WPKH keep public keys hidden until funds are spent.
Lost Bitcoin Wallets Add Pressure
Quantus also highlighted the issue of lost Bitcoin wallets. According to the report, between 2.3 million and 3.7 million BTC are likely inaccessible because owners lost their private keys.
That total includes coins believed to belong to Bitcoin creator Satoshi Nakamoto. Since those wallets could not be moved by their owners, the report warned they could become permanent targets once quantum attacks become practical.
Auryn Macmillan, co-founder of Gnosis Guild, said in comments included in the report that vulnerable accounts may need a hard migration deadline. Under that approach, tokens left in exposed accounts would be frozen after the deadline.
Such a step would be controversial for Bitcoin. It would require broad agreement across a network that has historically resisted changes affecting ownership, custody, and user choice.
Post-Quantum Standards Already Exist
The wider technology industry has already started preparing for post-quantum cryptography. NIST finalized post-quantum encryption standards in August 2024, including ML-DSA, ML-KEM and SLH-DSA.
Quantus said companies such as Google, Signal, Apple and Cloudflare have begun deploying post-quantum protections. Some migration targets extend into 2029 and 2030.
Bitcoin’s transition is more complex. The report pointed to governance coordination, scaling limits, and the challenge of replacing existing signature systems without creating new weaknesses.
Post-quantum signatures are also larger than Bitcoin’s current signatures. The material cited research that modeled lower throughput, higher fees, and greater storage needs during a migration.
Custody Firms Begin Testing
Institutional custody firms are starting to test post-quantum infrastructure. BitGo said on May 26 that it completed a post-quantum signature transaction on Sepolia, an Ethereum testnet, with Silence Laboratories.
The test combined ML-DSA-44 with MPC, or multiparty computation. MPC allows private-key control to be distributed among several parties without giving any one party full access.
BitGo said the simulated transaction showed how post-quantum signatures could fit into an institutional custody workflow. The setup preserved distributed key control, policy enforcement, and operational separation of duties.
However, other custody and infrastructure firms are also studying post-quantum migration. Fireblocks, Dfns Labs, and Anchorage Digital have all reported work tied to quantum-resistant systems or Bitcoin migration research.
Related: Quantum Threat Forces Crypto Industry Into Defense Mode
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