Bitcoin’s path to quantum resistance is shaping up as a multi-year coordination challenge rather than an immediate hardware emergency, according to Ledger CTO Charles Guillemet. In a technical analysis published September 16, 2026, Guillemet evaluated the SHRINCS post-quantum signature draft, a Bitcoin Improvement Proposal authored by Conduition, Ethan Heilman, Mikhail Kudinov, Oleksandr Kurbatov, Jonas Nick, and remix7531.
The SHRINCS proposal specifies post-quantum signature sizes ranging from 548 to 5,777 bytes, a major increase from the 64 to 72 bytes typical of current ECDSA and Schnorr schemes. The design combines stateful signatures using Flexible XMSS and WOTS+C with a stateless fallback mechanism backed by SHA-256. Guillemet noted this hash-based approach avoids introducing additional hardness assumptions such as lattice-based cryptography and targets Category 1 security under NIST standards. The draft sets a 48-byte public key; stateful signatures range from 548 to 4,619 bytes, while the stateless fallback reaches 5,777 bytes.
Guillemet warned that waiting for a cryptographically relevant quantum computer to emerge would create operational risk because research, testing, and network-wide deployment could take years. The compact stateful pathway uses one-time keys structured in a Merkle tree and requires signers to maintain a persistent counter that never rolls back. An accidental backup restore or concurrent signing event could trigger cryptographic slot reuse and enable third-party signature forgery. If state desynchronization occurs, the seed phrase can generate a stateless signature, shifting the trade-off toward block-space consumption rather than fund loss.
The analysis also highlights practical wallet challenges: hash-based key generation and stateless signature computation could take several minutes on contemporary secure hardware devices. The model does not preserve unhardened derivation under BIP32 or the compact threshold signature schemes native to Schnorr. Although per-byte verification is computationally lighter than BIP340 Schnorr because it relies mainly on SHA-256, larger transaction sizes would directly affect network bandwidth, storage overhead, and full-node operation. Guillemet added that achieving social consensus on dormant coins whose public keys have never been exposed may be more complex than choosing the mathematical standard itself.
Meanwhile, on September 17, BitGo introduced its Quantum Resistance Scorer, a tool that checks user addresses for quantum-related vulnerabilities and emphasizes that not all bitcoin is equally exposed to such risks. The launch comes as the broader crypto market shows mixed signals and cautious investor sentiment; BitGo framed the scorer as part of growing security awareness amid rapid advances in quantum computing. Ledger also continues to face legal pressure from a class-action lawsuit filed August 27, 2026 in the U.S. District Court for the Southern District of New York, where plaintiffs seek at least $500 million in damages tied to prior data breaches.
