Ledger CTO Analyzes SHRINCS Post-Quantum Signature Proposal for Bitcoin
Ledger Chief Technology Officer Charles Guillemet published a technical analysis on September 16, 2026, evaluating the SHRINCS post-quantum signature proposal for Bitcoin. The draft Bitcoin Improvement Proposal (BIP) specifies signature sizes ranging from 548 to 5,777 bytes, a significant increase from the 64 to 72 bytes used in current ECDSA and Schnorr schemes.
Quantum Migration Timeline and Operational Risk
Guillemet warned that Bitcoin’s quantum migration represents a protracted technical coordination challenge rather than an immediate hardware threat. The evaluation emphasizes that waiting for cryptographically relevant quantum computers to emerge would create substantial operational risk, given the years required for research, testing, and network-wide deployment of quantum-resistant solutions.
The current Bitcoin custody framework relies on digital signatures vulnerable to quantum attacks. SHRINCS, authored by Conduition, Ethan Heilman, Mikhail Kudinov, Oleksandr Kurbatov, Jonas Nick, and remix7531, addresses this by relying exclusively on SHA-256 hash functions—Bitcoin’s native algorithm—avoiding additional hardness assumptions like lattice-based cryptography while targeting NIST Category 1 security standards.
Technical Specifications and Trade-offs
The draft establishes a 48-byte public key. Stateful signatures range from 548 to 4,619 bytes, while the stateless fallback signature reaches 5,777 bytes. This contrasts sharply with Bitcoin’s current space efficiency and introduces unprecedented operational requirements for custodial software and hardware.
State Management Challenges
The scheme uses one-time keys structured in a Merkle tree, requiring signers to maintain a persistent counter that never rolls back. Accidental backup restoration or concurrent signing events could trigger cryptographic slot reuse, enabling third-party signature forgery. If state desynchronization or data loss occurs, the seed phrase generates a 5,777-byte stateless signature, shifting the trade-off toward block space consumption rather than fund loss.
Performance and Compatibility Constraints
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 compact threshold signature schemes native to Schnorr. However, per-byte verification is computationally lighter than BIP340 Schnorr, consisting primarily of SHA-256 operations.
Guillemet noted that larger transaction sizes will directly impact network bandwidth, storage overhead, and the ability of everyday users to operate full nodes.
Governance and Community Consensus
Beyond algorithmic parameters, the transition presents major community governance dilemmas. Achieving social consensus on the fate of dormant coins whose public keys have never been exposed to the blockchain looms as a more complex hurdle than selecting the mathematical standard itself.
Ongoing Legal and Technical Context
Ledger continues to navigate legal challenges from a class-action lawsuit filed August 27, 2026, in the U.S. District Court for the Southern District of New York (Case 1:26-cv-07307-VM), where plaintiffs seek at least $500 million in damages tied to prior data breaches. Technical discussions surrounding the SHRINCS draft will continue across Bitcoin developer mailing lists pending formal reviews of its security proofs.