Post-quantum Internet Key Exchange via Authenticated Forward-Secure KEM

In this work, we present a new framework for signature-free, post-quantum secure authenticated key exchange (AKE) that simultaneously satisfies: (1) exchanging at most two standard ciphertexts of a key encapsulation mechanism (KEM); (2) computational symmetry; (3) perfect forward secrecy (PFS); (4) strong resilience to secret-state exposure; (5) strong resistance to decryption-error attacks; (6) admitting instantiations based on the native structure of ML-KEM under the MLWE assumption; and (7) provable security in both the random oracle model (ROM) and the quantum-accessible random oracle model (QROM) under the post-id $\mathsf{eCK}\mbox{-}\mathsf{PFS}$ framework. This resolves several fundamental open questions in the literature. The core technical building block is a new cryptographic primitive, called an authenticated forward-secure KEM (AFS-KEM), which unifies authentication and forward secrecy within a single KEM abstraction and may be of independent interest.