Paper 2026/914

Post-Quantum Authenticated Key Exchange via Signcryption with Ephemeral Key Masking

Abstract

We present PQES-AKE, a novel two-party authenticated key exchange (AKE) protocol built upon the Post-Quantum Encryption and Signcryption Scheme (PQES) introduced by Kara et al. The protocol achieves mutual authentication, session key secrecy, and forward secrecy in a post-quantum adversarial model. The central design principle of PQES-AKE is the concealment of ephemeral Diffie-Hellman (DH) keys within affine masks derived from randomness generated internally by the PQES signcryption algorithm. The security of PQES-AKE rests on three hardness assumptions, including Learning With Errors (LWE) for ciphertext confidentiality, a Secret-Base Discrete Exponentiation (SBDE) assumption for signature unforgeability, and the Computational Diffie-Hellman (CDH) assumption for session key secrecy. The protocol completes in two network rounds, with a total communication cost of approximately 627 bytes, and requires 17 modular exponentiations. A Python prototype evaluated on a commodity Intel Core i7 laptop achieves an average execution time of 6.2ms. These results confirm that PQES-AKE provides a competitive, single-primitive alternative to composite KEM-then-authenticate constructions in post-quantum secure channel establishment.