Bird of Prey 2: non-malleable Schnorr + PQ signatures

The discussion revolves around the integration and compatibility of cryptographic schemes, particularly focusing on the BoP2 scheme. It is noted that BoP2 does not operate in a black-box manner with any SUF-CMA Post-Quantum (PQ) signature scheme, indicating a lack of black-box compatibility with classical cryptographic systems. This compatibility is considered less crucial according to the insights derived from referenced materials.

In the realm of cryptographic security, there's consideration given to stateful schemes that could potentially fail if misused. Such vulnerabilities present a case for adopting hybrid schemes, which combine elements of different cryptographic approaches. These hybrid forms are touted as beneficial for signers who might not handle state management accurately and consistently. Despite their theoretical advantage in enhancing security, the complexity and the necessity to maintain Elliptic Curve (EC) signatures indefinitely make them less appealing in practical scenarios.

Looking towards future developments, the conversation suggests that if cryptographic schemes based on novel assumptions such as lattices or isogenies are to be adopted, they should likely be implemented in hybrid forms initially. Specifically, for lattice-based systems, adding a minor amount of additional data to large witnesses would be trivial in terms of computational overhead. Conversely, for compact schemes like isogenies, hybridizing with EC could result in a noticeable increase in witness size, approximately by a factor of 1.3x. There's an anticipation of potential soft-forks to remove unnecessary components if isogenies gain more trust and widespread acceptance in the future. Additionally, designing schemes to allow optional hybridization from the outset could offer flexibility to signers regarding security protocol adoption.