An efficient certificateless authenticated key agreement protocol without bilinear pairings

Certificateless public key cryptography simplifies the complex certificate management in the traditional public key cryptography and resolves the key escrow problem in identity-based cryptography. Many certificateless authenticated key agreement protocols using bilinear pairings have been proposed. But the relative computation cost of the pairing is approximately twenty times higher than that of the scalar multiplication over elliptic curve group. Recently, several certificateless authenticated key agreement protocols without pairings were proposed to improve the performance. In this paper, we propose a new certificateless authenticated key agreement protocol without pairing. The user in our just needs to compute five scale multiplication to finish the key agreement. We also show the proposed protocol is secure in the random oracle model

Distributed Key Generation for the Internet

Although distributed key generation (DKG) has been studied for some time, it has never been examined outside of the synchronous setting. We present the first realistic DKG architecture for use over the Internet. We propose a practical system model and define an efficient verifiable secret sharing scheme in it. We observe the necessity of Byzantine agreement for asynchronous DKG and analyze the difficulty of using a randomized protocol for it. Using our verifiable secret sharing scheme and a leader-based agreement protocol, we then design a DKG protocol for public-key cryptography. Finally, along with traditional proactive security, we also introduce group modification primitives in our system.

A Certificateless One-Way Group Key Agreement Protocol for Point-to-Point Email Encryption

Over the years, email has evolved and grown to one of the most widely used form of communication between individuals and organizations. Nonetheless, the current information technology standards do not value the significance of email security in today\u27s technologically advanced world. Not until recently, email services such as Yahoo and Google started to encrypt emails for privacy protection. Despite that, the encrypted emails will be decrypted and stored in the email service provider\u27s servers as backup. If the server is hacked or compromised, it can lead to leakage and modification of one\u27s email. Therefore, there is a strong need for point-to-point (P2P) email encryption to protect email user\u27s privacy. P2P email encryption schemes strongly rely on the underlying Public Key Cryptosystems (PKC). The evolution of the public key cryptography from the traditional PKC to the Identity-based PKC (ID-PKC) and then to the Certificateless PKC (CL-PKC) provides a better and more suitable cryptosystem to implement P2P email encryption. Many current public-key based cryptographic protocols either suffer from the expensive public-key certificate infrastructure (in traditional PKC) or the key escrow problem (in ID-PKC). CL-PKC is a relatively new cryptosystem that was designed to overcome both problems. In this thesis, we present a CL-PKC group key agreement protocol, which is, as the author\u27s knowledge, the first one with all the following features in one protocol: (1) certificateless and thus there is no key escrow problem and no public key certificate infrastructure is required. (2) one-way group key agreement and thus no back-and-forth message exchange is required; (3) n-party group key agreement (not just 2- or 3-party); and (4) no secret channel is required for key distribution. With the above features, P2P email encryption can be implemented securely and efficiently. This thesis provides a security proof for the proposed protocol using ``proof by simulation\u27\u27. Efficiency analysis of the protocol is also presented in this thesis. In addition, we have implemented the prototypes (email encryption systems) in two different scenarios in this thesis

Identity-Based Authenticated Asymmetric Group Key Agreement Protocol

In identity-based public-key cryptography, an entity\u27s public key can be easily derived from its identity. The direct derivation of public keys in identity-based public-key cryptography eliminates the need for certificates and solves certain public key management problems in traditional public-key cryptosystems. Recently, the notion of asymmetric group key agreement was introduced, in which the group members merely negotiate a common encryption key which is accessible to any entity, but they hold respective secret decryption keys. In this paper, we first propose a security model for identity-based authenticated asymmetric group key agreement (IB-AAGKA) protocols. We then propose an IB-AAGKA protocol which is proven secure under the Bilinear Di±e-Hellman Exponent assumption. Our protocol is also efficient, and readily adaptable to provide broadcast encryption

A Certificateless One-Way Group Key Agreement Protocol for End-to-End Email Encryption

Over the years, email has evolved into one of the most widely used communication channels for both individuals and organizations. However, despite near ubiquitous use in much of the world, current information technology standards do not place emphasis on email security. Not until recently, webmail services such as Yahoo\u27s mail and Google\u27s gmail started to encrypt emails for privacy protection. However, the encrypted emails will be decrypted and stored in the service provider\u27s servers. If the servers are malicious or compromised, all the stored emails can be read, copied and altered. Thus, there is a strong need for end-to-end (E2E) email encryption to protect email user\u27s privacy. In this paper, we present a certificateless one-way group key agreement protocol with the following features, which are suitable to implement E2E email encryption: (1) certificateless and thus there is no key escrow problem and no public key certificate infrastructure is required; (2) one-way group key agreement and thus no back-and-forth message exchange is required; and (3) n-party group key agreement (not just 2- or 3-party). This paper also provides a security proof for the proposed protocol using proof by simulation . Finally, efficiency analysis of the protocol is presented at the end of the paper

Efficient and Dynamic Group Key Agreement in Ad hoc Networks

Confidentiality, integrity and authentication are more relevant issues in Ad hoc networks than in wired fixed networks. One way to address these issues is the use of symmetric key cryptography, relying on a secret key shared by all members of the network. But establishing and maintaining such a key (also called the session key) is a non-trivial problem. We show that Group Key Agreement (GKA) protocols are suitable for establishing and maintaining such a session key in these dynamic networks. We take an existing GKA protocol, which is robust to connectivity losses and discuss all the issues for good functioning of this protocol in Ad hoc networks. We give implementation details and network parameters, which significantly reduce the computational burden of using public key cryptography in such networks

Short expressions of permutations as products and cryptanalysis of the Algebraic Eraser

On March 2004, Anshel, Anshel, Goldfeld, and Lemieux introduced the \emph{Algebraic Eraser} scheme for key agreement over an insecure channel, using a novel hybrid of infinite and finite noncommutative groups. They also introduced the \emph{Colored Burau Key Agreement Protocol (CBKAP)}, a concrete realization of this scheme. We present general, efficient heuristic algorithms, which extract the shared key out of the public information provided by CBKAP. These algorithms are, according to heuristic reasoning and according to massive experiments, successful for all sizes of the security parameters, assuming that the keys are chosen with standard distributions. Our methods come from probabilistic group theory (permutation group actions and expander graphs). In particular, we provide a simple algorithm for finding short expressions of permutations in $S_n$, as products of given random permutations. Heuristically, our algorithm gives expressions of length $O(n^2\log n)$, in time and space $O(n^3)$. Moreover, this is provable from \emph{the Minimal Cycle Conjecture}, a simply stated hypothesis concerning the uniform distribution on $S_n$. Experiments show that the constants in these estimations are small. This is the first practical algorithm for this problem for $n\ge 256$. Remark: \emph{Algebraic Eraser} is a trademark of SecureRF. The variant of CBKAP actually implemented by SecureRF uses proprietary distributions, and thus our results do not imply its vulnerability. See also arXiv:abs/12020598Comment: Final version, accepted to Advances in Applied Mathematics. Title slightly change

Constructions in public-key cryptography over matrix groups

ISBN : 978-0-8218-4037-5International audienceThe purpose of the paper is to give new key agreement protocols (a multi-party extension of the protocol due to Anshel-Anshel-Goldfeld and a generalization of the Diffie-Hellman protocol from abelian to solvable groups) and a new homomorphic public-key cryptosystem. They rely on difficulty of the conjugacy and membership problems for subgroups of a given group. To support these and other known cryptographic schemes we present a general technique to produce a family of instances being matrix groups (over finite commutative rings) which play a role for these schemes similar to the groups $Z_n^*$ in the existing cryptographic constructions like RSA or discrete logarithm