Anonymous messaging system allows users to deliver messages without revealing the sending content and their identifiers, which has attracted ongoing concerns. However, to the best of our knowledge, all the existing solutions still fail to protect users’ privacy under coercion. That is, the user’s communication transcripts might be tracked and cached, and later coerced to reveal the underlying messages associated with the ciphertexts due to law enforcement reasons or for evil purposes. In addition, anonymity alone is not enough for some practical scenarios. For instance, a journalist just wants to communicate with those intended informants, and thereby gather information from anonymous but authenticated sources. In this paper, to address the above-mentioned issues, we introduce an authenticated and deniable anonymous messaging framework. Its core component is a new cryptographic primitive dubbed deniable identity-based matchmaking encryption (DIB-ME), which captures plausible deniability under coercion and mutual authentication without interactions simultaneously. We further present a concrete DIB-ME construction and prove its security in the random oracle model. The performance analysis indicates merits of the proposed DIB-ME scheme. We also implement the proposed DIB-ME construction and present extensive experiment results, as a proof of concept to demonstrate its soundness and practicability.

A EU Regulation from 2019 aims to achieve a minimal degree of interoperability of personal identity documents in Europe (eID). In particular, eID document verification should be performed according to ICAO protocols, including biometric verification. At the same time, additional functionalities implemented by the Member States must not interfere with the obligatory ICAO part. As presenting personal data from an eID requires an explicit consent of the eID owner, PACE - a password authenticated key exchange (PAKE) protocol, the core part of the ICAO specification - must be used. A side effect of the EU Regulation are problems regarding already deployed additional functionalities, such as digital signatures. In this paper we present a pragmatic approach for solving this problem. Instead of installing these functionalities independently - e.g. at a cost of extra code on the eID chip and potential compatibility problems - we may reuse the basic ICAO protocols. As an example of this approach we show a proof-of-presence protocol derived from PACE.