Ledger CTO: Public Keys Already Exposed, Quantum Risk Is Real

TL;DR

• Quantum computers could break Bitcoin’s cryptography and expose private keys.
• Ledger tests post-quantum signatures inside secure hardware elements.
• Buterin outlined a roadmap to protect Ethereum from quantum attacks.

The arrival of sufficiently powerful quantum computers could break the cryptographic foundations of Bitcoin and other cryptocurrencies. Charles Guillemet, Chief Technology Officer at hardware wallet maker Ledger, issued a warning about the vulnerability of Elliptic Curve Cryptography, the system that protects private keys. While large-scale quantum computers do not exist today, Guillemet argues that the industry cannot afford a “wait and see” approach. Preparation must begin years before the technology becomes a reality.

Guillemet explained that blockchain security depends on the difficulty of reversing certain mathematical operations. Elliptic Curve Cryptography makes it nearly impossible to derive a private key from a public key using classical computers. Quantum machines, however, could solve those equations rapidly. If that happens, anyone who knows a public key could compute the corresponding private key and drain funds.

What does post-quantum computing actually mean in daily life? Kicking off a series on PQC in hardware signers. @DonjonLedger explores what matters in practice: implementing PQ signatures inside Secure Elements under real embedded constraints and threat models. 🧵 pic.twitter.com/9uGtbXUzf5

— Charles Guillemet (@P3b7_) February 27, 2026

The common assumption that Bitcoin public keys remain hidden does not hold in practice. When users spend coins, they reveal the public key. Many early Bitcoin transactions, including those from the network’s first years, used a format called pay-to-public-key that placed the public key directly on the blockchain.

Guillemet pointed out that approximately seven million bitcoins, out of a circulating supply of 19.99 million, currently face exposure. That figure includes around one million coins attributed to Satoshi Nakamoto.

The Industry Moves to Build Defenses Against Future Quantum Attacks

Ledger runs experiments with post-quantum cryptography inside its secure elements, the chips that store private keys offline. Guillemet detailed two families of quantum-resistant signature schemes.

Hash-based signatures offer strong security and have undergone years of study, but they produce large signatures that consume space. Lattice-based signatures provide better scalability and smaller sizes, though researchers have studied them for a shorter period.

Implementing these schemes inside hardware signers presents major challenges. Ledger tests run entirely in software, without hardware acceleration, directly inside secure elements. RAM pressure and computational cost remain severe bottlenecks. The secure environment that keeps keys safe also limits processing power and memory. Moving from theory to working products requires solving those engineering constraints.

Ethereum co-founder Vitalik Buterin addressed the same threat on Thursday. He outlined a roadmap to protect the Ethereum blockchain from quantum computers over the long term. Practical quantum machines capable of breaking current cryptography do not yet exist, but the window for preparation narrows as research advances. Both Bitcoin and Ethereum face the same underlying risk: the cryptographic algorithms that secure them today will not hold forever.

Now, scaling.

There are two buckets here: short-term and long-term.

Short term scaling I've written about elsewhere. Basically:

* Block level access lists (coming in Glamsterdam) allow blocks to be verified in parallel.
* ePBS (coming in Glamsterdam) has many features, of…

— vitalik.eth (@VitalikButerin) February 27, 2026

The warning from Ledger’s CTO reinforces a growing consensus in the crypto industry. Waiting for the first quantum attack would leave funds exposed and trigger panic. Building and deploying post-quantum signatures takes years, and upgrading live blockchains requires coordination across developers, miners, and users. The work starts now, before the threat arrives.