A New ID-based Signature with Batch Verification

An identity (ID)-based signature scheme allows any pair of users to communicate securely and to verify each other\u27s signatures without exchanging public key certificates. We have several ID-based signatures based on the discrete logarithm problem. While they have an advantage that the system secret can be shared by several parties through threshold schemes, they have a critical disadvantage in efficiency. To enhance the efficiency of verification, we propose a new ID-based signature scheme that allows batch verification of multiple signatures. The verification cost of the proposed signature scheme for $k$ signatures is almost constant with minimal security loss and when a new signature by a different signer is added to the batch verification, the additional cost is almost a half of that of a single signature. We prove that the proposed signature scheme is secure against existential forgery under adaptively chosen message and ID attack in the random oracle model and show why other ID-based signature schemes are hard to achieve these properties

On the security of a certificateless aggregate signature scheme

Aggregate signature can combinensignatures on nmessages fromnusers into a single short signature, and the resulting signature can convince the verifier that thenusers indeed signed the ncorresponding messages. This feature makes aggregate signature very useful especially in environments with low bandwidth communication, low storage and low computability since it greatly reduces the total signature length and verification cost. Recently, Xiong et al. presented an efficient certificateless aggregate signature scheme. They proved that their scheme is secure in a strengthened security model, where the “malicious-but-passive” KGC attack was considered. In this paper, we show that Xiong et al.’s certificateless aggregate signature scheme is not secure even in a weaker security model called “honest-but-curious” KGC attack model

Efficient Revocable ID-Based Signature With Cloud Revocation Server

Over the last few years, identity-based cryptosystem (IBC) has attracted widespread attention because it avoids the high overheads associated with public key certificate management. However, an unsolved but critical issue about IBC is how to revoke a misbehaving user. There are some revocable identity-based encryption schemes that have been proposed recently, but little work on the revocation problem of identity-based signature has been undertaken so far. One approach for revocation in identity-based settings is to update users\u27 private keys periodically, which is usually done by the key generation center (KGC). But with this approach, the load on the KGC will increase quickly when the number of users increases. In this paper, we propose an efficient revocable identity-based signature (RIBS) scheme in which the revocation functionality is outsourced to a cloud revocation server (CRS). In our proposed approach, most of the computations needed during key-updates are offloaded to the CRS. We describe the new framework and the security model for the RIBS scheme with CRS and we prove that the proposed scheme is existentially unforgeable against adaptively chosen messages and identity attacks in the random oracle model. Furthermore, we monstrate that our scheme outperforms previous IBS schemes in terms of lower computation and communication costs

On security of a Certificateless Aggregate Signature Scheme

Aggregate signatures are useful in special areas where the signatures on many different messages generated by many different users need to be compressed. Recently, Xiong et al. proposed a certificateless aggregate signature scheme provably secure in the random oracle model under the Computational Diffie-Hellman assumption. Unfortunately, by giving concrete attacks, we indicate that Xiong et al. aggregate signature scheme does not meet the basic requirement of unforgeability

Certicateless Aggregate Short Signature Scheme

An aggregate signature scheme is the aggregation of multiple signatures into a single compact signature of short string that can convince to any arbitrary verifier participating in the scheme. The aggregate signature scheme is very useful for real-world cryptographic applications such as secure routing, database outsourcing, etc. where the signatures on several distinct messages generated by many distinct users requires to be compact. In this paper, we presented an aggregate signature scheme using Certificateless Public Key Cryptography(CL-PKC). The scheme is provably secure with strongest security and shortest length. We have proven the scheme is existentially unforgeable under adaptive chosen message attack, assuming the hardness of computational Diffie-Hellman(CDH) Problem

Black-Box Constructions of Signature Schemes in the Bounded Leakage Setting

To simplify the certificate management procedures, Shamir introduced the concept of identity-based cryptography (IBC). However, the key escrow problem is inherent in IBC. To get rid of it, Al-Riyami and Paterson introduced in 2003 the notion of certificateless cryptography (CLC). However, if a cryptosystem is not perfectly implemented, adversaries would be able to obtain part of the system\u27s secret state via side-channel attacks, and thus may break the system. This is not considered in the security model of traditional cryptographic primitives. Leakage-resilient cryptography was then proposed to prevent adversaries from doing so. There are fruitful works on leakage-resilient encryption schemes, while there are not many on signature schemes in the leakage setting. In this work, we review the folklore generic constructions of identity-based signature and certificateless signature, and show that if the underlying primitives are leakage-resilient, so are the resulting identity-based signature scheme and certificateless signature scheme. The leakage rate follows the minimum one of the underlying primitives. We also show some instantiations of these generic constructions

Research on security and privacy in vehicular ad hoc networks

Los sistemas de redes ad hoc vehiculares (VANET) tienen como objetivo proporcionar una plataforma para diversas aplicaciones que pueden mejorar la seguridad vial, la eficiencia del tráfico, la asistencia a la conducción, la regulación del transporte, etc. o que pueden proveer de una mejor información y entretenimiento a los usuarios de los vehículos. Actualmente se está llevando a cabo un gran esfuerzo industrial y de investigación para desarrollar un mercado que se estima alcance en un futuro varios miles de millones de euros. Mientras que los enormes beneficios que se esperan de las comunicaciones vehiculares y el gran número de vehículos son los puntos fuertes de las VANET, su principal debilidad es la vulnerabilidad a los ataques contra la seguridad y la privacidad.En esta tesis proponemos cuatro protocolos para conseguir comunicaciones seguras entre vehículos. En nuestra primera propuesta empleamos a todas las unidades en carretera (RSU) para mantener y gestionar un grupo en tiempo real dentro de su rango de comunicación. Los vehículos que entren al grupo de forma anónima pueden emitir mensajes vehículo a vehículo (V2V) que inmediatamente pueden ser verificados por los vehículos del mismo grupo (y grupos de vecinos). Sin embargo, en la primera fase del despliegue de este sistema las RSU pueden no estar bien distribuídas. Consecuentemente, se propone un conjunto de mecanismos para hacer frente a la seguridad, privacidad y los requisitos de gestión de una VANET a gran escala sin la suposición de que las RSU estén densamente distribuidas. La tercera propuesta se centra principalmente en la compresión de las evidencias criptográficas que nos permitirán demostrar, por ejemplo, quien era el culpable en caso de accidente. Por último, investigamos los requisitos de seguridad de los sistemas basados en localización (LBS) sobre VANETs y proponemos un nuevo esquema para la preservación de la privacidad de la localización en estos sistemas sobre dichas redes.Vehicular ad hoc network (VANET) systems aim at providing a platform for various applications that can improve traffic safety and efficiency, driver assistance, transportation regulation, infotainment, etc. There is substantial research and industrial effort to develop this market. It is estimated that the market for vehicular communications will reach several billion euros. While the tremendous benefits expected from vehicular communications and the huge number of vehicles are strong points of VANETs, their weakness is vulnerability to attacks against security and privacy.In this thesis, we propose four protocols for secure vehicle communications. In our first proposal, we employ each road-side unit (RSU) to maintain and manage an on-the-fly group within its communication range. Vehicles entering the group can anonymously broadcast vehicle-to-vehicle (V2V) messages, which can be instantly verified by the vehicles in the same group (and neighbor groups). However, at the early stage of VANET deployment, the RSUs may not be well distributed. We then propose a set of mechanisms to address the security, privacy, and management requirements of a large-scale VANET without the assumption of densely distributed RSUs. The third proposal is mainly focused on compressing cryptographic witnesses in VANETs. Finally, we investigate the security requirements of LBS in VANETs and propose a new privacy-preserving LBS scheme for those networks