Generally vehicles in VANETs should periodically broadcast safety messages. Since safety messages contain traffic related information and are sensitive to location privacy, it is essential to ensure anonymity, authenticity and traceability in broadcast. These conflicting requirements make it difficult to design a secure communication scheme for VANETs. In this paper, we propose a signature sche...

Linkable ring signatures have found many attractive applications. One of the recent important extensions is a linkable threshold ring signature (LTRS) scheme. Unfortunately, the existing LTRS schemes are only secure in the random oracle model (ROM). In this paper, we make the following contributions. First, we construct the first LTRS scheme that is secure without requiring the ROM. Further, we...

Recently, Chen, Chung, and Huang proposed a traceable proxy multisignature scheme based on the elliptic curve cryptosystem. However, this paper shows that the original signers can produce a valid signature as the proxy signer does in the proxy protected scheme. Therefore, Chen et al.’s proxy-protected scheme cannot protect the proxy signer from being forged by the original signers. We further f...

This thesis is divided into two distinct parts. The first part of the thesis explores various deniable signature schemes and their applications. Such schemes do not bind a unique public key to a message, but rather specify a set of entities that could have created the signature, so each entity involved in the signature can deny having generated it. The main deniable signature schemes we examine...

Group signatures were introduced by Chaum and Van Heyst [12], and many security requirements for group signatures have been proposed. Bellare, Micciancio, and Warinschi [4] showed that satisfying full-anonymity and full-traceability is sufficient, in the sence that all the above-mentioned requirements are implied by them. Wilson and Menezes [5] introduced a considerable attack against standard ...

Due to the development of Internet communication technology, E-Commerce is becoming popular. Because crime is thriving, avoiding malicious behavior and protecting property becomes an important issue. To prevent malicious behavior, many proposals have been put forth. The subliminal channel is the most popular method, which notifies the designated receiver to transmit secret messages. Simmons was...

A digraph D is traceable if it contains a path visiting every vertex, and hypotraceable if D is not traceable, but D − v is traceable for every vertex v ∈ V (D). Van Aardt, Frick, Katrenic̃ and Nielsen [Discrete Math. 11(2011), 1273-1280] showed that there exists a hypotraceable oriented graph of order n for every n > 8, except possibly for n = 9 or 11. These two outstanding existence questions ...

Ring signature is a kind of group-oriented signature. It allows amember of a group to sign messages on behalf of the group withoutrevealing his/her identity. Certificateless public key cryptography wasfirst introduced by Al-Riyami and Paterson in Asiacrypt 2003. Incertificateless cryptography, it does not require the use of certificatesto guarantee the authenticity of users’...

Abstract Ring signatures enable a user to sign messages on behalf of an arbitrary set users, called the ring, without revealing exactly which member that ring actually generated signature. The signer-anonymity property makes have been active research topic. Recently, Park and Sealfon (PS; CRYPTO’19) presented important anonymity notion named signer-unclaimability constructed lattice-based signa...