This survey reviews the two most prominent group-oriented anonymous signature schemes and analyzes the existing approaches for their problem: balancing anonymity against traceability. Group signatures and ring signatures are the two leading competitive signature schemes with a rich body of research. Both group and ring signatures enable user anonymity with group settings. Any group user can produce a signature while hiding his identity in a group. Although group signatures have predefined group settings, ring signatures allow users to form ad-hoc groups. Preserving user identities provided an advantage for group and ring signatures. Thus, presently many applications utilize them. However, standard group signatures enable an authority to freely revoke signers’ anonymity. Thus, the authority might weaken the anonymity of innocent users. On the other hand, traditional ring signatures maintain permanent user anonymity, allowing space for malicious user activities; thus achieving the requirements of privacy-preserved traceability in group signatures and controlled anonymity in ring signatures has become desirable. This paper reviews group and ring signatures and explores the existing approaches that address the identification of malicious user activities. We selected many papers that discuss balancing user tracing and anonymity in group and ring signatures. Since this paper scrutinizes both signatures from their basic idea to obstacles including tracing users, it provides readers a broad synthesis of information about two signature schemes with the knowledge of current approaches to balance excessive traceability in group signatures and extreme anonymity in ring signatures. This paper will also shape the future research directions of two critical signature schemes that require more awareness.

Vehicular Ad-hoc NETworks (VANETs), a special kind of Mobile Ad-hoc NETworks (MANETs), play an important role in Intelligent Transportation Systems (ITS). Via wireless technology, vehicles exchange information related to road conditions and their status, and, thereby, VANETs enhance transportation safety and efficiency. A critical aspect of VANETs is providing privacy for the vehicles. The employment of pseudonym certificates is a well-known solution to the privacy problems in VANETs. However, certificate management faces challenges in renewing certificates and revoking vehicles. The centralized certificate management, especially resulting in the delay of the revocation process, harms the nodes of VANETs. This paper proposes a blockchain structure-based certificate management for VANETs and voting-based revocation to halt misbehaving vehicles’ actions. Moreover, this paper presents extended privacy for the participants of the voting process using ring signatures.