A concrete certificateless signature scheme without pairings

Certificateless public key cryptography was introduced to avoid the inherent key escrow problem in identity-based cryptography, and eliminate the use of certificates in traditional PKI. Most cryptographic schemes in certificateless cryptography are built from bilinear mappings on elliptic curves which need costly operations. Despite the investigation of certificateless public key encryption without pairings, certificateless signature without pairings received much less attention than what it deserves. In this paper, we present a concrete pairing-free certificateless signature scheme for the first time. Our scheme is more computationally efficient than others built from pairings. The new scheme is provably secure in the random oracle model assuming the hardness of discrete logarithm problem.

Efficient and short certificateless signatures secure against realistic adversaries

The notion of certificateless cryptography is aimed to eliminate the use of certificates in traditional public key cryptography and also to solve the key-escrow problem in identity-based cryptography. Many kinds of security models have been designed for certificateless cryptography and many new schemes have been introduced based on the correspondence of the security models. In generally speaking, a stronger security model can ensure a certificateless cryptosystem with a higher security level, but a realistic model can lead to a more efficient scheme. In this paper, we focus on the efficiency of a certificateless signature (CLS) scheme and introduce an efficient CLS scheme with short signature size. On one hand, the security of the scheme is based on a realistic model. In this model, an adversary is not allowed to get any valid signature under false public keys. On the other hand, our scheme is as efficient as BLS short signature scheme in both communication and computation and, therefore, turns out to be more efficient than other CLS schemes proposed so far. We provide a rigorous security proof of our scheme in the random oracle model. The security of our scheme is based on the k-CAA hard problem and a new discovered hard problem, namely the modified k-CAA problem. Our scheme can be applied to systems where signatures are typed in by human or systems with low-bandwidth channels and/or low-computation power.

Certificateless ignatures: New schemes and security models

We present a study of security in certificateless signatures. We divide potential adversaries according to their attack power, and for the first time, three new kinds of adversaries are introduced into certificateless signatures. They are Normal Adversary, Strong Adversary and Super Adversary (ordered by their attack power). Combined with the known Type I Adversary and Type II Adversary in certificateless cryptography, we then define the security of certificateless signatures in different attack scenarios. Our new security models, together with others in the literature, provide a clear definition of the security in certificateless signatures. Two concrete schemes with different security levels are also proposed in this paper. The first scheme, which is proven secure (in the random oracle model) against Normal Type I and Super Type II adversaries, has the shortest signature length among all known certificateless signature schemes. The second scheme is secure (in the random oracle model) against Super Type I and Type II adversaries. Compared with another scheme that has a similar security level, our second scheme requires less operational cost but a little longer signature length. Two server-aided verification protocols are also proposed to reduce the verification cost on the verifier.

Cryptanalysis and improvement of an efficient certificateless signature scheme

In traditional digital signature schemes, certificates signed by a trusted party are required to ensure the authenticity of the public key. In Asiacrypt 2003, the concept of certificateless signature scheme was introduced. The advantage of certificate-less public key cryptography successfully eliminates the necessity of certificates in the traditional public key cryptography and simultaneously solves the inherent key escrow problem suffered in identity-based cryptography. Recently, Yap et al. proposed an efficient certificateless signature scheme and claimed that their scheme is existentially unforgeable in the random oracle model. In this paper, we show that the certificateless signature scheme proposed by Yap et al. is insecure against public key replacement attacks. Furthermore, we propose an improved certificateless signature scheme, which is existentially unforgeable against adaptive chosen message attacks under the computational Diffie-Hellman assumption in the random oracle model and provide the security proof of the proposed scheme.

The 0-1 Knapsack polytope – a starting point for cryptanalysis of Knapsack ciphers?

The Knapsack Cryptosystem of Merkle and Hellman, 1978, is one of the earliest public-key cryptography schemes. The security of the method relies on the difficulty in solving Subset Sum Problems (also known as Knapsack Problems). In this paper, we first provide a brief history of knapsack-based cryptosystems and their cryptanalysis attacks. Following that, we review the advances in integer programming approaches to 0 − 1 Knapsack Problems, with a focus on the polyhedral studies of the convex hull of the integer set. Last of all, we discuss potential future research directions in applying integer programming in the cryptanalysis of knapsack ciphers.

An efficient anonymous remote attestation scheme for trusted computing based on improved CPK

 The platform remote attestation (RA) is one of the main features of trusted computing platform proposed by the trusted computing group (TCG). The privacy certificate authority (CA) solution of RA requires users to pay for multiple certificates, and the direct anonymous attestation (DAA) solution leads to inefficiency. TCG RA also suffers from limitations of platform configuration privacy. This paper proposed a RA scheme based on an improved combined public key cryptography (ICPK) (abbreviated to RA-ICPK). RA-ICPK is a certificate-less scheme without using public key infrastructure CA signature or DAA signature, which combines commitment scheme, zero-knowledge proof and ring signature (RS) to own the property of unforgeability and privacy. RA-ICPK is mainly based on elliptic curve cryptography without bilinear pair computing, and only carries out zero-knowledge proof one time. RA-ICPK need not depend on trusted third parties to check trusted platform modules identity and integrity values revocations. © 2014 Springer Science+Business Media New York

A strong provably secure IBE scheme without bilinear map

Identity-based encryption (IBE) allows one party to send ciphered messages to another using an arbitrary identity string as an encryption key. Since IBE does not require prior generation and distribution of keys, it greatly simplifies key management in public-key cryptography. According to the Menezes-Okamoto-Vanstone (MOV) reduction theory, the IBE scheme based on bilinear map loses the high efficiency of elliptic curve because of the requirement of large security parameters. Therefore, it is important to build a provably secure IBE scheme without bilinear map. To this end, this paper proposes an improved IBE scheme that is different from the previous schemes because this new scheme does not use symmetric encryption algorithm. Furthermore, it can be proven to be secure against adaptively chosen identity and chosen plaintext attacks in the standard model. Elaborated security and performance analysis demonstrate that this new scheme outperforms the previous ones in terms of the time complexity for encryption and decryption.

Um algoritmo de criptografia de chave pública semanticamente seguro baseado em curvas elípticas

Esta dissertação apresenta o desenvolvimento de um novo algoritmo de criptografia de chave pública. Este algoritmo apresenta duas características que o tornam único, e que foram tomadas como guia para a sua concepção. A primeira característica é que ele é semanticamente seguro. Isto significa que nenhum adversário limitado polinomialmente consegue obter qualquer informação parcial sobre o conteúdo que foi cifrado, nem mesmo decidir se duas cifrações distintas correspondem ou não a um mesmo conteúdo. A segunda característica é que ele depende, para qualquer tamanho de texto claro, de uma única premissa de segurança: que o logaritmo no grupo formado pelos pontos de uma curva elíptica de ordem prima seja computacionalmente intratável. Isto é obtido garantindo-se que todas as diferentes partes do algoritmo sejam redutíveis a este problema. É apresentada também uma forma simples de estendê-lo a fim de que ele apresente segurança contra atacantes ativos, em especial, contra ataques de texto cifrado adaptativos. Para tanto, e a fim de manter a premissa de que a segurança do algoritmo seja unicamente dependente do logaritmo elíptico, é apresentada uma nova função de resumo criptográfico (hash) cuja segurança é baseada no mesmo problema.

A secret sharing scheme based on exponentiation in Galois fields

To provide more efficient and flexible alternatives for the applications of secret sharing schemes, this paper describes a threshold sharing scheme based on exponentiation of matrices in Galois fields. A significant characteristic of the proposed scheme is that each participant has to keep only one master secret share which can be used to reconstruct different group secrets according to the number of threshold values.

Context-enhanced authentication for infrastructureless network environments

Infrastructureless networks are becoming more popular with the increased prevalence of wireless networking technology. A significant challenge faced by these infrastructureless networks is that of providing security. In this paper we examine the issue of authentication, a fundamental component of most security approaches, and show how it can be performed despite an absence of trusted infrastructure and limited or no existing trust relationship between network nodes. Our approach enables nodes to authenticate using a combination of contextual information, harvested from the environment, and traditional authentication factors (such as public key cryptography). Underlying our solution is a generic threshold signature scheme that enables distributed generation of digital certificates.

Computer Democracy - Our Next Step in Europe

After about a quarter of a century of enlightened development and ongoing preparatory technological, scientific and political activities we are arrived at the realization period of the idea. The two major technological vehicles of progress are the World Wide Web, the most democratic international forum of information exchange and the advent of public key cryptography as a combined philosophical and practical device of individual integrity and collective responsibility.

RSA-Based Password-Authenticated Key Exchange, Revisited

The RSA-based Password-Authenticated Key Exchange (PAKE) protocols have been proposed to realize both mutual authentication and generation of secure session keys where a client is sharing his/her password only with a server and the latter should generate its RSA public/private key pair (e, n), (d, n) every time due to the lack of PKI (Public-Key Infrastructures). One of the ways to avoid a special kind of off-line (so called e-residue) attacks in the RSA-based PAKE protocols is to deploy a challenge/response method by which a client verifies the relative primality of e and φ(n) interactively with a server. However, this kind of RSA-based PAKE protocols did not give any proof of the underlying challenge/response method and therefore could not specify the exact complexity of their protocols since there exists another security parameter, needed in the challenge/response method. In this paper, we first present an RSA-based PAKE (RSA-PAKE) protocol that can deploy two different challenge/response methods (denoted by Challenge/Response Method1 and Challenge/Response Method2). The main contributions of this work include: (1) Based on the number theory, we prove that the Challenge/Response Method1 and the Challenge/Response Method2 are secure against e-residue attacks for any odd prime e; (2) With the security parameter for the on-line attacks, we show that the RSA-PAKE protocol is provably secure in the random oracle model where all of the off-line attacks are not more efficient than on-line dictionary attacks; and (3) By considering the Hamming weight of e and its complexity in the RSA-PAKE protocol, we search for primes to be recommended for a practical use. We also compare the RSA-PAKE protocol with the previous ones mainly in terms of computation and communication complexities.

Time-Independent Discrete Gaussian Sampling for Post-Quantum Cryptography

As the development of a viable quantum computer nears, existing widely used public-key cryptosystems, such as RSA, will no longer be secure. Thus, significant effort is being invested into post-quantum cryptography (PQC). Lattice-based cryptography (LBC) is one such promising area of PQC, which offers versatile, efficient, and high performance security services. However, the vulnerabilities of these implementations against side-channel attacks (SCA) remain significantly understudied. Most, if not all, lattice-based cryptosystems require noise samples generated from a discrete Gaussian distribution, and a successful timing analysis attack can render the whole cryptosystem broken, making the discrete Gaussian sampler the most vulnerable module to SCA. This research proposes countermeasures against timing information leakage with FPGA-based designs of the CDT-based discrete Gaussian samplers with constant response time, targeting encryption and signature scheme parameters. The proposed designs are compared against the state-of-the-art and are shown to significantly outperform existing implementations. For encryption, the proposed sampler is 9x faster in comparison to the only other existing time-independent CDT sampler design. For signatures, the first time-independent CDT sampler in hardware is proposed. 

The case for quantum key distribution

Quantum key distribution (QKD) promises secure key agreement by using quantum mechanical systems. We argue that QKD will be an important part of future cryptographic infrastructures. It can provide long-term confidentiality for encrypted information without reliance on computational assumptions. Although QKD still requires authentication to prevent man-in-the-middle attacks, it can make use of either information-theoretically secure symmetric key authentication or computationally secure public key authentication: even when using public key authentication, we argue that QKD still offers stronger security than classical key agreement.