Paper 2020/1279

Tightly-Secure Authenticated Key Exchange, Revisited

Tibor Jager, Eike Kiltz, Doreen Riepel, and Sven Schäge


We introduce new tightly-secure authenticated key exchange (AKE) protocols that are extremely efficient, yet have only a constant security loss and can be instantiated in the random oracle model both from the standard DDH assumption and a subgroup assumption over RSA groups. These protocols can be deployed with optimal parameters, independent of the number of users or sessions, without the need to compensate a security loss with increased parameters and thus decreased computational efficiency. We use the standard “Single-Bit-Guess” AKE security (with forward secrecy and state corruption) requiring all challenge keys to be simultaneously pseudo-random. In contrast, most previous papers on tightly secure AKE protocols (Bader et al., TCC 2015; Gjøsteen and Jager, CRYPTO 2018; Liu et al., ASIACRYPT 2020) concentrated on a non-standard “Multi-Bit-Guess” AKE security which is known not to compose tightly with symmetric primitives to build a secure communication channel. Our key technical contribution is a new generic approach to construct tightly-secure AKE protocols based on non-committing key encapsulation mechanisms. The resulting DDH-based protocols are considerably more efficient than all previous constructions.

Available format(s)
Public-key cryptography
Publication info
Preprint. MINOR revision.
Authenticated key exchangetightnessnon-committing encryptionforward security
Contact author(s)
doreen riepel @ rub de
eike kiltz @ rub de
tibor jager @ uni-wuppertal de
sven schaege @ rub de
2020-11-13: last of 2 revisions
2020-10-14: received
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      author = {Tibor Jager and Eike Kiltz and Doreen Riepel and Sven Schäge},
      title = {Tightly-Secure Authenticated Key Exchange, Revisited},
      howpublished = {Cryptology ePrint Archive, Paper 2020/1279},
      year = {2020},
      note = {\url{}},
      url = {}
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