International Association for Cryptologic Research

International Association
for Cryptologic Research


Ying Wang


Receiver-Anonymity in Reradomizable RCCA-Secure Cryptosystems Resolved 📺
In this work, we resolve the open problem raised by Prabhakaran and Rosulek at CRYPTO 2007, and present the first anonymous, rerandomizable, Replayable-CCA (RCCA) secure public key encryption scheme. This solution opens the door to numerous privacy-oriented applications with a highly desired RCCA security level. At the core of our construction is a non-trivial extension of smooth projective hash functions (Cramer and Shoup, EUROCRYPT 2002), and a modular generic framework developed for constructing Rand-RCCA-secure encryption schemes with receiver-anonymity. The framework gives an enhanced abstraction of the original Prabhakaran and Rosulek’s scheme (which was the first construction of Rand-RCCA-secure encryption in the standard model), where the most crucial enhancement is the first realization of the desirable property of receiver-anonymity, essential to privacy settings. It also serves as a conceptually more intuitive and generic understanding of RCCA security, which leads, for example, to new implementations of the notion. Finally, note that (since CCA security is not applicable to the privacy applications motivating our work) the concrete results and the conceptual advancement presented here, seem to substantially expand the power and relevance of the notion of Rand-RCCA-secure encryption.
Identity-Based Encryption for Fair Anonymity Applications: Defining, Implementing, and Applying Rerandomizable RCCA-secure IBE
Our context is anonymous encryption schemes hiding their receiver, but in a setting which allows authorities to reveal the receiver when needed. While anonymous Identity-Based Encryption (IBE) is a natural candidate for such fair anonymity (it gives trusted authority access by design), the {\it de facto} security standard (a.k.a. IND-ID-CCA) is incompatible with the ciphertext rerandomizability which is crucial to anonymous communication. Thus, we seek to extend IND-ID-CCA security for IBE to a notion that can be meaningfully relaxed for rerandomizability while it still protects against active adversaries. To the end, inspired by the notion of replayable adaptive chosen-ciphertext attack (RCCA) security (Canetti {\it et al.}, Crypto'03), we formalize a new security notion called Anonymous Identity-Based RCCA (ANON-ID-RCCA) security for rerandomizable IBE and propose the first construction with rigorous security analysis. The core of our scheme is a novel extension of the double-strand paradigm, which was originally proposed by Golle {\it et al.} (CT-RSA'04) and later extended by Prabhakaran and Rosulek (Crypto'07), to the well-known Gentry-IBE (Eurocrypt'06). Notably, our scheme is the first IBE that simultaneously satisfies adaptive security, rerandomizability, and recipient-anonymity to date. As the application of our new notion, we design a new universal mixnet in the identity-based setting that does not require public key distribution (with fair anonymity). More generally, our new notion is also applicable to most existing rerandomizable RCCA-secure applications to eliminate the need for public key distribution infrastructure while allowing fairness.
Chameleon Signature from Bilinear Pairing
Chameleon signatures are non-interactive signatures based on a hash-and-sign paradigm, and similar in efficiency to regular signatures. The distinguishing characteristic of chameleon signatures is that there are non-transferable, with only the designated recipient capable of asserting its validity. In this paper, we introduce a new ID-based chameleon hash function based on bilinear pairing and build the ID-based chameleon signature scheme. Compared with the conventional chameleon hashing functions, the owner of a public hash key in the ID-based chameleon hashing scheme does not necessarily need to retrieve the associated secret key. The scheme enjoys all the attributes in the normal chameleon signature and the added characteristics of ID-based cryptography based on bilinear pairing.
ID-based Authenticated Two Round Multi-Party Key Agreement
This paper proposes an ID-based authenticated two round multi-party key agreement among n parties. Several ID-based two-party and tripartite key agreement schemes were proposed recently. Our two round multi-party key agreement scheme utilizes the idea of the two-round group key exchange protocol of Burmester and Desmedt. The authenticity of the protocol is assured by a special signature scheme, so the messages carrying the information of ephemeral key can be broadcasted authentically by an entity. Security attributes of our protocol are presented, and computational overhead and band width of the broadcast messages are analyzed as well.
An Improved ID-based Authenticated Group Key Agreement Scheme
Authenticated group key agreement problem is important in many modern collaborative and distributed applications. There are two ID-based authenticated group key agreement schemes have been proposed by Choi et al. and us, which are based on bilinear pairings and BD scheme. Recently, Zhang and Chen propose an impersonation attack on the two schemes, which means the schemes are not fully authenticated. In this paper, we propose an improved ID-based authenticated group key agreement scheme which can resist this attack.