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

The discussion around hybrid cryptographic schemes, particularly those involving a mix of elliptic curve (EC) and post-quantum cryptography (PQC), raises several key points. Firstly, the notion that no hybrid scheme utilizing both constituent schemes in a black-box manner can achieve signature unforgeability under chosen message attacks (SUF-CMA) is highlighted. This challenges the development of straightforward hybrid implementations but does not completely rule out their potential effectiveness.

Regarding the practicality of such schemes, there's skepticism about the necessity and utility of hybrid scripts, especially given the minimal concerns over post-quantum EC signature malleation. The focus, instead, is suggested to remain on hash-based schemes due to their lower security assumptions, which are deemed adequate for most current applications. However, the idea of incorporating stateful schemes that could potentially fail under misuse presents an argument for considering hybrids, particularly as a precautionary measure against operational errors.

Looking forward, if cryptographic schemes based on novel assumptions, such as lattices or isogenies, were to be integrated, it might be prudent to include them only within a hybrid framework. This approach could mitigate risks associated with the adoption of pure PQC schemes, which may not yet have gained widespread trust. Concerns from Bitcoin holders about the security of using purely PQC schemes for asset protection reinforce the cautious stance towards their immediate full-scale implementation. Thus, exploring hybrid schemes could provide a foundational strategy for enhancing security while maintaining confidence among users in blockchain technologies.