Huaxiong Wang

Pushing the limits: a very compact and a threshold implementation of AES

Our contribution is twofold: first we describe a very compact hardware implementation of AES-128, which requires only 2400 GE. This is to the best of our knowledge the smallest implementation reported so far. Then we apply the threshold countermeasure by Nikova et al. to the AES S-box and yield an implementation of the AES improving the level of resistance against first-order side-channel attacks. Our experimental results on real-world power traces show that although our implementation provides additional security, it is still susceptible to some sophisticated attacks having enough number of measurements.

Universal Designated-Verifier Signatures

Motivated by privacy issues associated with dissemination of signed digital certificates, we define a new type of signature scheme called a ‘Universal Designated-Verifier Signature’ (UDVS). A UDVS scheme can function as a standard publicly-verifiable digital signature but has additional functionality which allows any holder of a signature (not necessarily the signer) to designate the signature to any desired designated-verifier (using the verifier’s public key). Given the designated-signature, the designated-verifier can verify that the message was signed by the signer, but is unable to convince anyone else of this fact.

Two-factor mutual authentication based on smart cards and passwords

One of the most commonly used two-factor user authentication mechanisms nowadays is based on smart-card and password. A scheme of this type is called a smart-card-based password authentication scheme. The core feature of such a scheme is to enforce two-factor authentication in the sense that the client must have the smart-card and know the password in order to gain access to the server. In this paper, we scrutinize the security requirements of this kind of schemes, and propose a new scheme and a generic construction framework for smart-card-based password authentication. We show that a secure password based key exchange protocol can be efficiently transformed to a smart-card-based password authentication scheme provided that there exist pseudorandom functions and target collision resistant hash functions. Our construction appears to be the first one with provable security. In addition, we show that two recently proposed schemes of this kind are insecure.

Efficient Extension of Standard Schnorr/RSA Signatures into Universal Designated-Verifier Signatures

Universal Designated-Verifier Signature (UDVS) schemes are digital signature schemes with additional functionality which allows any holder of a signature to designate the signature to any desired designated-verifier such that the designated-verifier can verify that the message was signed by the signer, but is unable to convince anyone else of this fact. Since UDVS schemes reduce to standard signatures when no verifier designation is performed, it is natural to ask how to extend the classical Schnorr or RSA signature schemes into UDVS schemes, so that the existing key generation and signing implementation infrastructure for these schemes can be used without modification. We show how this can be efficiently achieved, and provide proofs of security for our schemes in the random oracle model.

Side-Channel Resistant Crypto for Less than 2,300 GE

A provably secure countermeasure against first order side-channel attacks was proposed by Nikova et al. (P. Ning, S. Qing, N. Li (eds.) International conference in information and communications security. Lecture notes in computer science, vol. 4307, pp. 529–545, Springer, Berlin, 2006). We have implemented the lightweight block cipher PRESENT using the proposed countermeasure. For this purpose we had to decompose the S-box used in PRESENT and split it into three shares that fulfill the properties of the scheme presented by Nikova et al. (P. Lee, J. Cheon (eds.) International conference in information security and cryptology. Lecture notes in computer science, vol. 5461, pp. 218–234, Springer, Berlin, 2008). Our experimental results on real-world power traces show that this countermeasure provides additional security. Post-synthesis figures for an ASIC implementation require only 2,300 GE, which makes this implementation suitable for low-cost passive RFID-tags.

Linear authentication codes: bounds and constructions

In this paper, we consider a new class of unconditionally secure authentication codes, called linear authentication codes (or linear A-codes). We show that a linear A-code can be characterized by a family of subspaces of a vector space over a finite field. We then derive an upper bound on the size of the source space when other parameters of the system, that is, the sizes of the key space and the authenticator space, and the deception probability, are fixed. We give constructions that are asymptotically close to the bound and show applications of these codes in constructing distributed authentication systems.

Advanced meet-in-the-middle preimage attacks : first results on full Tiger, and improved results on MD4 and SHA-2

We revisit narrow-pipe designs that are in practical use, and their security against preimage attacks. Our results are the best known preimage attacks on Tiger, MD4, and reduced SHA-2, with the result on Tiger being the first cryptanalytic shortcut attack on the full hash function. Our attacks runs in time 2188.8 for finding preimages, and 2188.2 for second-preimages. Both have memory requirement of order 28, which is much less than in any other recent preimage attacks on reduced Tiger. Using pre-computation techniques, the time complexity for finding a new preimage or second-preimage for MD4 can now be as low as 278.4 and 269.4 MD4 computations, respectively. The second-preimage attack works for all messages longer than 2 blocks.

New results on multi-receiver authentication codes

Multi-receiver authentication is an extension of traditional point-to-point message authentication in which a sender broadcasts a single authenticated message such that all the receivers can independently verify the authenticity of the message, and malicious groups of up to a given size of receivers can not successfully impersonate the transmitter, or substitute a transmitted message. This paper presents some new results on unconditionally secure multi-receiver authentication codes. First we generalize a polynomial construction due to Desmedt, Frankel and Yung, to allow multiple messages be authenticated with each key. Second, we propose a new flexible construction for multi-receiver A-code by combining an A-code and an (n, m, k)-cover-free family. Finally, we introduce the model of multi-receiver A-code with dynamic sender and present an efficient construction for that.

Multireceiver authentication code4: models, bounds, constructions, and extensions

Multireceiver authentication codes allow one sender to construct an authenticated message for a group of receivers such that each receiver can verify authenticity of the received message. In this paper, we give a formal definition of multireceiver authentication codes, derive information theoretic and combinatorial lower bounds on their performance, and give new efficient and flexible constructions for such codes. Finally, we extend the basic model to the case that multiple messages are sent and the case that the sender can be any member of the group.

Efficient one-time proxy signatures

One-time proxy signatures are one-time signatures for which a primary signer can delegate his or her signing capability to a proxy signer. In this work we propose two one-time proxy signature schemes with different security properties. Unlike other existing one-time proxy signatures that are constructed from public key cryptography, our proposed schemes are based one-way functions without trapdoors and so they inherit the communication and computation efficiency from the traditional one-time signatures. Although from a verifier point of view, signatures generated by the proxy are indistinguishable from those created by the primary signer, a trusted authority can be equipped with an algorithm that allows the authority to settle disputes between the signers. In our constructions, we use a combination of one-time signatures, oblivious transfer protocols and certain combinatorial objects. We characterise these new combinatorial objects and present constructions for them.