This paper studies how a simple approach based on fuzzing testing can help authors of Solidity contracts to accurately estimate the gas cost of services specified in a contract. Our fuzzer creates a private blockchain and randomly generates transactions. Such an environment is meant to simulate large scale behavior that may be seen in a public blockchain. Our fuzzer handles Ethereum starting and target endpoints in a transaction to accommodate requirements expressed in financial contracts. By comparing the gas computation made by the Ethereum Solidity compiler and the actual consumption during our fuzzing, we are able to find discrepancies between predicted and real gas consumption. Our findings are beneficial to transaction authors to correctly predict the computing resources of Ethereum miners.

Yao et al. (A note on the feasibility of generalized universal composability.Theory and Applications of Models of Computationpp. 474–485, 2007; A note on the feasibility of generalised universal composability.Mathematical Structures in Computer Science,19(1), pp. 193–205) claimed a potential limitation on the class of protocols that could be securely implemented in the generalized universal composability (GUC) framework proposed by Canetti et al. (Universally composable security with global setup.Lecture Notes in Computer Science, pp. 61–85, 2007). Specifically, Yao et al. presented a concrete attack on a GUC Zero Knowledge (GUCZK) protocol, a natural adaptation Blum's ZK proof for Directed Hamiltonicity using the general GUC feasibility of Canetti et al. (Universally composable security with global setup.Lecture Notes in Computer Science, pp. 61–85, 2007). Interestingly, the attack was not analysed in the GUC model in Yao et al. (A note on the feasibility of generalised universal composability.Mathematical Structures in Computer Science19(1), pp. 193–205, 2009) but in theFUC model, a new UC-like framework proposed in the same work. Nonetheless, Yao et al. (A note on the feasibility of generalised universal composability.Mathematical Structures in Computer Science19(1), pp. 193–205, 2009) argued that, in light of this attack, GUC would lose its concurrent general composability and proof of knowledge properties. Concretely, they argue that GUC composability would now be with respect to some adversaries with limited access to external arbitrary protocols. In this work, we show that the claimed attack from Yao et al. is indeed harmless and does not contradict the security of the mentioned GUCZK protocol, thus restoring the general feasibility for GUC.

Anonymous communication protocols must achieve two seemingly contradictory goals: privacy (informally, they must guarantee the anonymity of the parties that send/receive information), and robustness (informally, they must ensure that the messages are not tampered). However, the long line of research that defines and analyzes the security of such mechanisms focuses almost exclusively on the former property and ignores the latter. In this paper, we initiate a rigorous study of robustness properties for anonymity protocols. We identify and formally define, using the style of modern cryptography, two related but distinct flavors of robustness. Our definitions are general (e.g. they strictly generalize the few existent notions for particular protocols) and flexible (e.g. they can be easily adapted to purely combinatorial/probabilistic mechanisms). We demonstrate the use of our definitions through the analysis of several anonymity mechanisms (Crowds, broadcast-based mix-nets, DC-nets, Tor). Notably, we analyze the robustness of a protocol by Golle and Juels for the dining cryptographers problem, identify a robustness-related weakness of the protocol, and propose and analyze a stronger version.

Phishing email fraud has been considered as one of the main cyber-threats over the last years. Its development has been closely related to social engineering techniques, where different fraud strategies are used to deceit a naïve email user. In this work, a latent semantic analysis and text mining methodology is proposed for the characterisation of such strategies, and further classification using supervised learning algorithms. Results obtained showed that the feature set obtained in this work is competitive against previous phishing feature extraction methodologies, achieving promising results over different benchmark machine learning classification techniques.

Simultaneous Broadcast protocols allow different parties to broadcast values in parallel while guaranteeing mutual independence of the broadcast values. In this work, we study various definitions of independence proposed in the literature by Chor, Goldwasser, Micali and Awerbuch (FOCS 1985), Chor and Rabin (PODC 1987) and Gennaro (IEEE Trans. on Parallel and Distributed Systems, 2000), and prove implications and separations among them. In summary, we show that each definition (generalized to allow arbitrary input distributions) is characterized by a class of “achievable” input distributions such that there is a single protocol that simultaneously meets the definition for all distributions in the class, while for any distribution outside the class no protocol can possibly achieve the definition. When comparing sets of achievable distributions, the definition of Gennaro is the most stringent (followed by the Chor and Rabin one, and Chor, Goldwasser, Micali and Awerbuch as the most relaxed) in the sense that it is achievable for the smallest class of distributions. This demonstrates that the definitions of Gennaro, and Chor and Rabin are of limited applicability. Then, we compare the definitions when restricted to achievable distributions. This time

We consider the problem of maintaining end-to-end security in the presence of intelligent proxies that may adaptively modify data being transmitted across a network. The video coding community considers this problem in the context of transcoding media streams, but their approaches either fail to address authentication or fail to provide meaningful security guarantees. We present two provably-secure schemes, LISSA and TRESSA, that allow an intelligent network intermediary to intercept a stream signed by a content provider, and adapt it dynamically, while preserving the ultimate receiver's ability to securely verify the content provider's signature (and, hence, authenticity and integrity of the data received). Our schemes allow the intermediary to selectively remove portions of the stream and, thus, permit common media transcoding techniques such as scalable compression and multiple file switching. Moreover, a content provider only has to encode and sign its entire data stream once, as opposed to nondynamically encoding and signing different versions for each anticipated combination of device, network configuration, and channel condition. Our implementation results demonstrate efficiency.

We study the vulnerability of two implementations of the Data Encryption Standard (DES) cryptosystem under a timing attack. A timing attack is a method, recently proposed by Paul Kocher, that is designed to break cryptographic systems. It exploits the engineering aspects involved in the implementation of cryptosystems and might succeed even against cryptosys-tems that remain impervious to sophisticated cryptanalytic techniques. A timing attack is, essentially, a way of obtaining some users private information by carefully measuring the time it takes the user to carry out cryptographic operations. In this work, we analyze two implementations of DES. We show that a timing attack yields the Hamming weight of the key used by both DES implementations. Moreover, the attack is computationally inexpensive. We also show that all the design characteristics of the target system, necessary to carry out the timing attack, can be inferred from timing measurements.