The advent of large-scale quantum computers threatens many cryptographic protocols used today. For fundamental primitives, such as key encapsulation mechanisms (KEMs) and signatures, standards are already available to achieve security against both classical and quantum adversaries (a.k.a. post-quantum security). However, for many complex protocols, achieving post-quantum security remains challenging. One possible source of difficulty is the non-black-box use of a building block. This is also the case for password-based protocols, such as password-authenticated key exchange (PAKE) and password-authenticated public-key encryption (PAPKE), which may handle KEM public keys as secret information. To protect such keys, recent constructions use password-based encryption mechanisms, utilizing Feistel networks, which in turn require hashing into the public-key space of the underlying KEM. Such hashing becomes non-trivial when the public-key space is structured. Although theoretical constructions exist for several KEMs, in many cases they have not yet been implemented, evaluated, and compared in practice.

Tasks to be performed by the student will include:

• Presenting the state of the art of hash-to-public-key constructions for KEMs.
• Studying the implementations of the corresponding KEMs, with special attention to public-key representations and key generation.
• Implementing hash-to-public-key constructions for various post-quantum secure KEMs.
• Evaluating and comparing the resulting implementations.
• Implementing a two-round Feistel-based encryption of KEM public keys and evaluating its performance for different KEMs with the goal of assessing their suitability for PAKE and PAPKE applications.