Marcos A. Simplicio

A family of implementation-friendly BN elliptic curves

Abstract: For the last decade, elliptic curve cryptography has gained increasing interest in industry and in the academic community. This is especially due to the high level of security it provides with relatively small keys and to its ability to create very efficient and multifunctional cryptographic schemes by means of bilinear pairings. Pairings require pairing-friendly elliptic curves and among the possible choices, Barreto-Naehrig (BN) curves arguably constitute one of the most versatile families. In this paper, we further expand the potential of the BN curve family. We describe BN curves that are not only computationally very simple to generate, but also specially suitable for efficient implementation on a very broad range of scenarios. We also present implementation results of the optimal ate pairing using such a curve defined over a 254-bit prime field.

Cryptanalysis of an efficient three-party password-based key exchange scheme

Three-party password-authenticated key exchange (3PAKE) protocols allow entities to negotiate a secret session key with the aid of a trusted server with whom they share a human-memorable password. Recently, Lou and Huang proposed a simple 3PAKE protocol based on elliptic curve cryptography, which is claimed to be secure and to provide superior efficiency when compared with similar-purpose solutions. In this paper, however, we show that the solution is vulnerable to key-compromise impersonation and offline password guessing attacks from system insiders or outsiders, which indicates that the empirical approach used to evaluate the schemes security is flawed. These results highlight the need of employing provable security approaches when designing and analyzing PAKE schemes. Copyright

Lyra: password-based key derivation with tunable memory and processing costs

We present Lyra, a password-based key derivation scheme based on cryptographic sponges. Lyra was designed to be strictly sequential (i.e., not easily parallelizable), providing strong security even against attackers that use multiple processing cores (e.g., custom hardware or a powerful GPU). At the same time, it is very simple to implement in software and allows legitimate users to fine-tune its memory and processing costs according to the desired level of security against brute force password guessing. We compare Lyra with similar-purpose state-of-the-art solutions, showing how our proposal provides a higher security level and overcomes limitations of existing schemes. Specifically, we show that if we fix Lyra ’s total processing time

I2TS01 - A Taxonomy for Locality Algorithms on Peer-to-Peer Networks

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Lyra2: Efficient Password Hashing with High Security against Time-Memory Trade-Offs

t in a legitimate platform, the cost of a memory-free attack against the algorithm is exponential, while the best-known result in the literature (namely, against the scrypt algorithm) is quadratic. In addition, for an identical same processing time, Lyra allows for a higher memory usage than its counterparts, further increasing the cost of brute force attacks.

Faster Isogeny-Based Compressed Key Agreement

Security in Wireless Sensor Networks (WSNs) is highly dependent on the behavior of the base station. This happens because, if the network is left unattended, sensor nodes cannot offload data to the (secure) base station in real time and, thus, until the base station becomes available, adversaries can compromise some sensor nodes and selectively destroy data. In order to prevent such attacks, providing the so-called “data survival”, some strategies can be employed. In this paper, we discuss and analyze different data survival strategies using cryptography. To the best of our knowledge, we provide the first implementation of such techniques, using a real sensor platform for their evaluation. As a result, we show that the main costs for the data survival process are not as high as it could be expected, and that strategies based on private keys can be used even if one considers the highly resource constrained nature of sensors.

Using Trade Wind to Sail in the Clouds

The continuous growth of peer-to-peer networks has made them responsible for a considerable portion of the current Internet traffic. For this reason, improvements in P2P network resources usage are of central importance. One effective approach for addressing this issue is the deployment of locality algorithms, which allow the system to optimize the peers selection policy for different network situations and, thus, maximize performance. To date, several locality algorithms have been proposed for use in P2P networks. However, they usually adopt heterogeneous criteria for measuring the proximity between peers, which hinders a coherent comparison between the different solutions. In this paper, we develop a thoroughly review of popular locality algorithms, based on three main characteristics: the adopted network architecture, distance metric, and resulting peer selection algorithm. As result of this study, we propose a novel and generic taxonomy for locality algorithms in peer-to-peer networks, aiming to enable a better and more coherent evaluation of any individual locality algorithm.

Demonstration of a framework for enabling security services collaboration across multiple domains

The Alred construction is a lightweight strategy for constructing message authentication algorithms from an underlying iterated block cipher. Even though this constructions original analyses show that it is secure against some attacks, the absence of formal security proofs in a strong security model still brings uncertainty on its robustness. In this paper, aiming to give a better understanding of the security level provided by different authentication algorithms based on this design strategy, we formally analyze two Alred variants—the Marvin message authentication code and the LetterSoup authenticated-encryption scheme,—bounding their security as a function of the attackers resources and of the underlying ciphers characteristics.