Time is money, friend! Timing Side-channel Attack against Garbled Circuit Constructions

With the advent of secure function evaluation (SFE), distrustful parties can jointly compute on their private inputs without disclosing anything besides the results. Yao’s garbled circuit protocol has become an integral part of secure computation thanks to considerable efforts made to make it feasible, practical, and more efficient. These efforts have resulted in multiple optimizations on this primitive to enhance its performance by orders of magnitude over the last years. The advancement in protocols has also led to the development of general-purpose compilers and tools made available to academia and industry. For decades, the security of protocols offered in those tools has been assured with regard to sound proofs and the promise that during the computation, no information on parties’ input would be leaking. In a parallel effort, however, side-channel analysis (SCA) has gained momentum in connection with the real-world implementation of cryptographic primitives. Timing side-channel attacks have proven themselves effective in retrieving secrets from implementations, even through remote access to them. Nevertheless, the vulnerability of garbled circuit frameworks to timing attacks has, surprisingly, never been discussed in the literature. This paper introduces Goblin, the first timing attack against commonly employed garbled circuit frameworks. Goblin is a machine learning-assisted, non-profiling, single-trace timing SCA, which successfully recovers the garbler’s input during the computation under different scenarios, including various GC frameworks, benchmark functions, and the number of garbler’s input bits. Furthermore, we discuss Gob- lin’s success factors and countermeasures against that. In doing so, Goblin hopefully paves the way for further research in this matter

Analysis of Https Overhead and Minimal Web Certificate Chain of Trust

The popularity of the web is indisputable. With the recent revelations about NSA spying and the increased need for privacy and security, the default use of secure web through TLS/SSL connections has been highlighted. However, the push back against enabling secure web connections by default is due to the increase in communication and processing time.In this work, we quantify the communication time for http and https download times for the most popular websites. The average download time over http non-persistent connection is 2.72 seconds while the average download time over https non-persistent connection is 3.156 seconds. The overhead in using encryption is thus only 436 milliseconds (about 4 round trip times on the Internet) or 16.1% for non-persistent connections. And for persistent connections the overhead is 15%. We thus make the case that https should be enabled by default due to the very low communications overhead. With the recent hacks and breaches at various certificate authorities and no-longer-trusted certificate authorities, we also quantified which certificate authorities are most popular on the Internet. By only trusting ten certificate authorities, a webbrowser can access almost 80% of https-enabled websites. The number of trusted certificate authorities can thus be reduced from thousands to a few dozen.Computer Scienc

Secure Authentication and Privacy-Preserving Techniques in Vehicular Ad-hoc NETworks (VANETs)

In the last decade, there has been growing interest in Vehicular Ad Hoc NETworks (VANETs). Today car manufacturers have already started to equip vehicles with sophisticated sensors that can provide many assistive features such as front collision avoidance, automatic lane tracking, partial autonomous driving, suggestive lane changing, and so on. Such technological advancements are enabling the adoption of VANETs not only to provide safer and more comfortable driving experience but also provide many other useful services to the driver as well as passengers of a vehicle. However, privacy, authentication and secure message dissemination are some of the main issues that need to be thoroughly addressed and solved for the widespread adoption/deployment of VANETs. Given the importance of these issues, researchers have spent a lot of effort in these areas over the last decade. We present an overview of the following issues that arise in VANETs: privacy, authentication, and secure message dissemination. Then we present a comprehensive review of various solutions proposed in the last 10 years which address these issues. Our survey sheds light on some open issues that need to be addressed in the future

Optimizing Registration Based Encryption

The recent work of Garg et al. from TCC\u2718 introduced the notion of registration based encryption (RBE). The principal motivation behind RBE is to remove the key escrow problem of identity based encryption (IBE), where the IBE authority is trusted to generate private keys for all the users in the system. Although RBE has excellent asymptotic properties, it is currently impractical. In our estimate, ciphertext size would be about 11 terabytes in an RBE deployment supporting 2 billion users. Motivated by this observation, our work attempts to reduce the concrete communication and computation cost of the current state-of-the-art construction. Our contribution is two-fold. First, we replace Merkle trees with crit-bit trees, a form of PATRICIA trie, without relaxing any of the original RBE efficiency requirements introduced by Garg et al. This change reduces the ciphertext size by 15% and the computation cost of decryption by 30%. Second, we observe that increasing RBE\u27s public parameters by a few hundred kilobytes could reduce the ciphertext size by an additional 50%. Overall, our work decreases the ciphertext size by 57.5%

Concurrently Secure Blind Schnorr Signatures

Many applications of blind signatures (notably in blockchains) require the resulting signatures to be compatible with the existing system. This makes schemes that produce Schnorr signatures (now being standardized and supported by major cryptocurrencies like Bitcoin) desirable. Unfortunately, the existing blind-signing protocol has been shown insecure when users can open signing sessions concurrently (Eurocrypt\u2721). On the other hand, only allowing sequential sessions opens the door to denial-of-service attacks. We present the first practical, concurrently secure blind-signing protocol for Schnorr signatures, using the standard primitives NIZK and PKE and assuming that Schnorr signatures themselves are unforgeable. We cast our scheme as a generalization of blind and partially blind signatures: we introduce the notion of predicate blind signatures, in which the signer can define a predicate that the blindly signed message must satisfy. We provide proof-of-concept implementations and benchmarks for various choices of primitives and scenarios, including blindly signing Bitcoin transactions conditioned on certain properties

Secure Multi-Party Computation In Practice

Secure multi-party computation (MPC) is a cryptographic primitive for computing on private data. MPC provides strong privacy guarantees, but practical adoption requires high-quality application design, software development, and resource management. This dissertation aims to identify and reduce barriers to practical deployment of MPC applications. First, the dissertation evaluates the design, capabilities, and usability of eleven state-of-the-art MPC software frameworks. These frameworks are essential for prototyping MPC applications, but their qualities vary widely; the survey provides insight into their current abilities and limitations. A comprehensive online repository augments the survey, including complete build environments, sample programs, and additional documentation for each framework. Second, the dissertation applies these lessons in two practical applications of MPC. The first addresses algorithms for assessing stability in financial networks, traditionally designed in a full-information model with a central regulator or data aggregator. This case study describes principles to transform two such algorithms into data-oblivious versions and benchmark their execution under MPC using three frameworks. The second aims to enable unlinkability of payments made with blockchain-based cryptocurrencies. This study uses MPC in conjunction with other privacy techniques to achieve unlinkability in payment channels. Together, these studies illuminate the limitations of existing software, develop guidelines for transforming non-private algorithms into versions suitable for execution under MPC, and illustrate the current practical feasibility of MPC as a solution to a wide variety of applications

Imbalanced Cryptographic Protocols

Efficiency is paramount when designing cryptographic protocols, heavy mathematical operations often increase computation time, even for modern computers. Moreover, they produce large amounts of data that need to be sent through (often limited) network connections. Therefore, many research efforts are invested in improving efficiency, sometimes leading to imbalanced cryptographic protocols. We define three types of imbalanced protocols, computationally, communicationally, and functionally imbalanced protocols. Computationally imbalanced cryptographic protocols appear when optimizing a protocol for one party having significantly more computing power. In communicationally imbalanced cryptographic protocols the messages mainly flow from one party to the others. Finally, in functionally imbalanced cryptographic protocols the functional requirements of one party strongly differ from the other parties. We start our study by looking into laconic cryptography, which fits both the computational and communicational category. The emerging area of laconic cryptography involves the design of two-party protocols involving a sender and a receiver, where the receiver’s input is large. The key efficiency requirement is that the protocol communication complexity must be independent of the receiver’s input size. We show a new way to build laconic OT based on the new notion of Set Membership Encryption (SME) – a new member in the area of laconic cryptography. SME allows a sender to encrypt to one recipient from a universe of receivers, while using a small digest from a large subset of receivers. A recipient is only able to decrypt the message if and only if it is part of the large subset. As another example of a communicationally imbalanced protocol we will look at NIZKs. We consider the problem of proving in zero-knowledge the existence of exploits in executables compiled to run on real-world processors. Finally, we investigate the problem of constructing law enforcement access systems that mitigate the possibility of unauthorized surveillance, as a functionally imbalanced cryptographic protocol. We present two main constructions. The first construction enables prospective access, allowing surveillance only if encryption occurs after a warrant has been issued and activated. The second allows retrospective access to communications that occurred prior to a warrant’s issuance