Universally Composable Relaxed Password Authenticated Key Exchange

Michel Abdalla (1) , Manuel Barbosa (2, 3) , Tatiana Bradley (4) , Stanisław Jarecki (4) , Jonathan Katz (5) , Jiayu Xu (5)

1 CASCADE - Construction and Analysis of Systems for Confidentiality and Authenticity of Data and Entities
2 INESC TEC - Institute for Systems and Computer Engineering, Technology and Science [Porto]
3 FCUP - Faculdade de Ciências da Universidade do Porto
4 UC Irvine - University of California [Irvine]
5 Volgenau School of Engineering - Department of Computer Science [Fairfax]

Protocols for password authenticated key exchange (PAKE) allow two parties who share only a weak password to agree on a cryptographic key. We revisit the notion of PAKE in the universal composabil-ity (UC) framework, and propose a relaxation of the PAKE functionality of Canetti et al. that we call lazy-extraction PAKE (lePAKE). Our relaxation allows the ideal-world adversary to postpone its password guess until after a session is complete. We argue that this relaxed notion still provides meaningful security in the password-only setting. As our main result, we show that several PAKE protocols that were previously only proven secure with respect to a "game-based" definition of security can be shown to UC-realize the lePAKE functionality in the random-oracle model. These include SPEKE, SPAKE2, and TBPEKE, the most efficient PAKE schemes currently known.

Domaines: Cryptographie et sécurité [cs.CR]

Michel Abdalla, Manuel Barbosa, Tatiana Bradley, Stanisław Jarecki, Jonathan Katz, et al.. Universally Composable Relaxed Password Authenticated Key Exchange. CRYPTO 2020 - 40th Annual International Cryptology Conference, Aug 2020, Santa Barbara / Virtual, United States. pp.278-307, ⟨10.1007/978-3-030-56784-2_10⟩. ⟨hal-02948678⟩