Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Theoretical Computer Science

Secret handshakes: Full dynamicity, deniability and lattice-based design

Zhiyuan An, Jing Pan, Yamin Wen, Fangguo Zhang

Published Oct 26, 2022• 6 citations
Publisher
DOI
10.1016/j.tcs.2022.10.035

Related papers

Expressive Cryptography: Lattice Perspectives

Xavier Boyen

Lecture notes in computer science•Jan 1, 2013•0 citations

DSH: Deniable Secret Handshake Framework

Yangguang Tian, Yingjiu Li, Yinghui Zhang +3 more

Lecture notes in computer science•Jan 1, 2018•8 citations

Lattice-Based Functional Commitments: Fast Verification and Cryptanalysis

Hoeteck Wee, David J. Wu

Lecture notes in computer science•Jan 1, 2023•27 citations

A Deniability Analysis of Signal’s Initial Handshake PQXDH

Rune Fiedler, Christian Janson

Many use messaging apps such as Signal to exercise their right to private communication. To cope with the advent of quantum computing, Signal employs a new initial handshake protocol called PQXDH for post-quantum confidentiality, yet keeps guarantees of authenticity and deniability classical. Compared to its predecessor X3DH, PQXDH includes a KEM encapsulation and a signature on the ephemeral key. In this work we show that PQXDH does not meet the same deniability guarantees as X3DH due to the signature on the ephemeral key. Our analysis relies on plaintext awareness of the KEM, which Signal's implementation of PQXDH does not provide. As for X3DH, both parties (initiator and responder) obtain different deniability guarantees due to the asymmetry of the protocol. For our analysis of PQXDH, we introduce a new model for deniability of key exchange that allows a more fine-grained analysis. Our deniability model picks up on the ideas of prior work and facilitates new combinations of deniability notions, such as deniability against malicious adversaries in the big brother model, i.e. where the distinguisher knows all secret keys. Our model may be of independent interest.

Proceedings on Privacy Enhancing Technologies•Jul 6, 2024•7 citations

The Quantum Handshake

J. G. Cramer

Springer eBooks•Dec 23, 2015•24 citations

AmphiKey: A Dual-Mode Secure Authenticated Key Encapsulation Protocol for Smart Grid

Kazi Hassan Shakib, Muhammad Asfand Hafeez, Arslan Munir

AmphiKey, a dual-mode post-quantum/traditional (PQ/T) hybrid authenticated key exchange mechanism (AKEM) has been designed to secure smart grid communications against both classical and quantum threats. AmphiKey offers two distinct operational modes within a single framework: an Authenticated Mode and a Deniable Mode. The Authenticated Mode employs a blackbox approach, combining ephemeral ML-KEM-768 and X25519 with long-term Raccoon DSA keys to provide forward secrecy and strong, non-repudiable authenticity. This design achieves "OR" confidentiality, where security holds if either of the KEMs is unbroken, and robust "AND" authenticity. For the signature operation, it leverages the 'masking-friendly' Raccoon digital signature (DSA), which is specifically designed for side-channel attack resistance, though this protection is localized to the signing key and does not provide deniability. In contrast, Deniable Mode provides deniable authentication, preserving privacy. The protocol used ML-KEM-768 (AKEM-1), Ephemeral X25519 (AKEM-2), Raccoon-based DSA (Rac) (compared performance to ML-DSA-65), and the Ascon cipher to deliver its security guarantees. Key contributions include providing a flexible protocol with enhanced security, optional deniability, and efficiency adapted to the diverse needs of the smart grid infrastructure. We present a comprehensive performance evaluation on a heterogeneous testbed featuring a powerful server and client (AMD Ryzen 5) and a resource-constrained client (Raspberry Pi). In efficient Deniable mode, the full handshake completes in 0.15 ms on the server and 0.41 ms on the Raspberry Pi client. In contrast, the Authenticated Mode is bottlenecked by the client-side signature generation; the handshake takes 4.8 ms for the Raspberry Pi client to initiate and 0.84 ms for the server to verify.

arXiv:2509.01701•Sep 1, 2025•0 citations
Many use messaging apps such as Signal to exercise their right to private communication. To cope with the advent of quantum computing, Signal employs a new initial handshake protocol called PQXDH for post-quantum confidentiality, yet keeps guarantees of authenticity and deniability classical. Compared to its predecessor X3DH, PQXDH includes a KEM encapsulation and a signature on the ephemeral key. In this work we show that PQXDH does not meet the same deniability guarantees as X3DH due to the signature on the ephemeral key. Our analysis relies on plaintext awareness of the KEM, which Signal's implementation of PQXDH does not provide. As for X3DH, both parties (initiator and responder) obtain different deniability guarantees due to the asymmetry of the protocol. For our analysis of PQXDH, we introduce a new model for deniability of key exchange that allows a more fine-grained analysis. Our deniability model picks up on the ideas of prior work and facilitates new combinations of deniability notions, such as deniability against malicious adversaries in the big brother model, i.e. where the distinguisher knows all secret keys. Our model may be of independent interest.
AmphiKey, a dual-mode post-quantum/traditional (PQ/T) hybrid authenticated key exchange mechanism (AKEM) has been designed to secure smart grid communications against both classical and quantum threats. AmphiKey offers two distinct operational modes within a single framework: an Authenticated Mode and a Deniable Mode. The Authenticated Mode employs a blackbox approach, combining ephemeral ML-KEM-768 and X25519 with long-term Raccoon DSA keys to provide forward secrecy and strong, non-repudiable authenticity. This design achieves "OR" confidentiality, where security holds if either of the KEMs is unbroken, and robust "AND" authenticity. For the signature operation, it leverages the 'masking-friendly' Raccoon digital signature (DSA), which is specifically designed for side-channel attack resistance, though this protection is localized to the signing key and does not provide deniability. In contrast, Deniable Mode provides deniable authentication, preserving privacy. The protocol used ML-KEM-768 (AKEM-1), Ephemeral X25519 (AKEM-2), Raccoon-based DSA (Rac) (compared performance to ML-DSA-65), and the Ascon cipher to deliver its security guarantees. Key contributions include providing a flexible protocol with enhanced security, optional deniability, and efficiency adapted to the diverse needs of the smart grid infrastructure. We present a comprehensive performance evaluation on a heterogeneous testbed featuring a powerful server and client (AMD Ryzen 5) and a resource-constrained client (Raspberry Pi). In efficient Deniable mode, the full handshake completes in 0.15 ms on the server and 0.41 ms on the Raspberry Pi client. In contrast, the Authenticated Mode is bottlenecked by the client-side signature generation; the handshake takes 4.8 ms for the Raspberry Pi client to initiate and 0.84 ms for the server to verify.