Paper 2026/1047 Original: eprint.iacr.org/2026/1047 ↗

Round-Optimal Subversion-Resilient UC PAKE from Malleable Trapdoor Smooth Projective Hash Functions

Abstract

Password-Authenticated Key Exchange (PAKE) allows two parties to establish a common high-entropy secret from a possibly low-entropy pre-shared secret such as a password. In this paper, we revisit the question of constructing PAKE protocols with subversion resilience in the framework of universal composability (UC), where the latter roughly means that UC security still holds even if one of the two parties is malicious and the honest party's code has been subverted (in an undetectable manner). The latter goal was recently achieved by Chakraborty, Magliocco, Magri and Venturi (ASIACRYPT 2024), based on sanitation of oblivious transfer protocols and dual-mode cryptosystems via cryptographic reverse firewalls (Mironov and Stephens-Davidowitz, EUROCRYPT 2015). Our contributions are as follows: - We introduce so-called malleable trapdoor smooth projective hash functions (M-TSPHF), as an enhancement of trapdoor smooth projective hash functions (Benhamouda et al., CRYPTO 2013). Our extension incorporates new properties including key malleability and element rerandomizability. - We give a generic construction of subversion-resilient UC PAKE based on M-TSPHF and other standard cryptographic primitives. As we demonstrate, our PAKE protocol can be instantiated efficiently yielding an improved round and communication complexity with respect to the previous protocol of Chakraborty et al. In particular, our PAKE protocol achieves round optimality, as it concludes in a single round.