Use of Composite FN-DSA Signatures in TLS 1.3

Compositing the post-quantum FN-DSA signature with traditional signature algorithms provides protection against potential breaks in either component. This document specifies how such a composite signature can be used for authentication in TLS 1.3. The selection of composite algorithms is intentionally chosen to strictly mirror the composite strategies for ML-DSA. This alignment provides two distinct and predictable security tiers for hybrid signatures, ensuring a consistent approach to post-quantum transition across the ecosystem.