Provable security is a very nice property for cryptographic protocols. Unfortunately, in many cases, this is at the cost of a considerable loss in terms of efficiency. More recently, a new approach to achieve some kind of provable security was explored using the so-called “random oracle model”. Last year, Stern and the author studied the security of blind signatures in this model. We first defi...

In order to protect the proxy signers’ privacy, many anonymous proxy signature schemes which are also called proxy ring signatures, have been proposed. Although the provable security in the random oracle model has received a lot of criticism, there is no provable secure anonymous proxy signature scheme without random oracles. In this paper, we propose the first provable secure anonymous proxy s...

This paper is brief tutorial on a technique for structuring security proofs as sequences games.

This thesis includes my research on efficient cryptographic protocols, sensor network key management, and radio frequency identification (RFID) authentication protocols. Key exchange, identification, and public key encryption are among the fundamental protocols studied in cryptography. There are two important requirements for these protocols: efficiency and security. Efficiency is evaluated usi...

We present two attacks on the security of the private grouping proof by Batina et al. [1]. We introduce the first formal models for yoking proofs. One model incorporates the aspect time, ensuring that the grouping proofs were generated at a specific time. A more general variant only provides a proof that tags were together at some time. Based on these models we propose two new protocols to gene...

Civitas is the first electronic voting system that is coercion-resistant, universally and voter verifiable, and suitable for remote voting. This paper describes the design and implementation of Civitas. Assurance is established in the design through security proofs, and in the implementation through information-flow security analysis. Experimental results give a quantitative evaluation of the t...

The elliptic curve cryptosystem (ECC) achieves the security level equivalent to that of digital signature algorithm (DSA), but has a lower computational cost and a smaller key size than the DSA. Till now so many proxy multi-signature schemes based on ECC without pairings have been proposed. To the best of our knowledge, none of them are provable secure. Having motivated, we first define a forma...

Identity-based (ID-based) public key cryptosystem can be a good alternative for certificate-based public key setting, especially when efficient key management and moderate security are required. A proxy signature scheme permits an entity to delegate its signing rights to another entity. But to date, no ID-based proxy signature scheme with provable security has been proposed. In this paper, we f...

Covert channels are designed to protect the communication relationship of sender and receiver. Traditional covert have become insecure due continuous improvement traffic analysis techniques. In this context, there is an urgent need identify new approaches for channels. Blockchain emerging technique with characteristics user anonymity, a flooding propagation mechanism, tamper resistance, which m...