Falcon support for quantum-resistant transactions

[jasny]

To future-proof LTO Network against potential quantum computing threats, we propose adding support for Falcon-512 as an optional signature scheme. This would allow users who are concerned about quantum security to opt-in to using Falcon without impacting standard transactions.

Rationale

• Quantum computing advancements are progressing faster than expected, with companies targeting 1M+ qubits in the coming years.
• ECDSA/secp256k1 and Ed25519 are not quantum-safe—eventually, they will need to be replaced.
• Falcon-512 is the smallest post-quantum signature scheme standardized by NIST, making it the most viable PQC option for blockchain use.
• An opt-in approach with an additional fee (e.g., 1 LTO per Falcon transaction) ensures minimal impact on network performance while allowing quantum-conscious users to upgrade early.

Proposed Implementation

• Allow Falcon-512 as an alternative signature scheme (alongside secp256k1/Ed25519).
• Require users to register a Falcon public key once per account to avoid including large public keys in every transaction.
• Charge an additional fee (e.g., 1 LTO per Falcon transaction) to compensate for increased storage and processing costs.
• Ensure backward compatibility—standard transactions remain unaffected.

Impact

• Future-proofs LTO Network against quantum threats.
• Minimal impact on blockchain performance, as adoption will be limited to users who opt-in.
• Allows LTO to position itself as one of the first quantum-ready blockchains.

Considerations

• Falcon signatures & public keys are significantly larger (~10x the size of current signatures).
• Storage and bandwidth considerations must be evaluated to prevent unnecessary blockchain bloat.

Libraries

• https://github.com/open-quantum-safe/liboqs-java
• https://github.com/java-crypto/cross_platform_crypto/blob/main/docs/pqc_falcon_liboqs_signature.md