333 research outputs found
On the practical use of physical unclonable functions in oblivious transfer and bit commitment protocols
In recent years, PUF-based schemes have been suggested not only for the basic tasks of tamper-sensitive key storage or the identification of hardware systems, but also for more complex protocols like oblivious transfer (OT) or bit commitment (BC), both of which possess broad and diverse applications. In this paper, we continue this line of research. We first present an attack on two recent OT and BC protocols which have been introduced by Brzuska et al. (CRYPTO, LNCS 6841, pp 51–70, Springer 2011). The attack quadratically reduces the number of CRPs which malicious players must read out to cheat, and fully operates within the original communication model of Brzuska et al. (CRYPTO, LNCS 6841, pp 51–70, Springer 2011). In practice, this leads to insecure protocols when electrical PUFs with a medium challenge-length are used (e.g., 64 bits), or whenever optical PUFs are employed. These two PUF types are currently among the most popular designs of so-called Strong PUFs. Secondly, we show that the same attack applies to a recent OT protocol of Ostrovsky et al. (IACR Cryptol. ePrint Arch. 2012:143, 2012), leading to exactly the same consequences. Finally, we discuss countermeasures. We present a new OT protocol with better security properties, which utilizes interactive hashing as a substep and is based on an earlier protocol by Rührmair (TRUST, LNCS 6101, pp 430–440, Springer 2010). We then closely analyze its properties, including its security, security amplification, and practicality
Knowledge Flow Analysis for Security Protocols
Knowledge flow analysis offers a simple and flexible way to find flaws in
security protocols. A protocol is described by a collection of rules
constraining the propagation of knowledge amongst principals. Because this
characterization corresponds closely to informal descriptions of protocols, it
allows a succinct and natural formalization; because it abstracts away message
ordering, and handles communications between principals and applications of
cryptographic primitives uniformly, it is readily represented in a standard
logic. A generic framework in the Alloy modelling language is presented, and
instantiated for two standard protocols, and a new key management scheme.Comment: 20 page
On the Robustness of Vision Transformers to Adversarial Examples
Recent advances in attention-based networks have shown that Vision
Transformers can achieve state-of-the-art or near state-of-the-art results on
many image classification tasks. This puts transformers in the unique position
of being a promising alternative to traditional convolutional neural networks
(CNNs). While CNNs have been carefully studied with respect to adversarial
attacks, the same cannot be said of Vision Transformers. In this paper, we
study the robustness of Vision Transformers to adversarial examples. Our
analyses of transformer security is divided into three parts. First, we test
the transformer under standard white-box and black-box attacks. Second, we
study the transferability of adversarial examples between CNNs and
transformers. We show that adversarial examples do not readily transfer between
CNNs and transformers. Based on this finding, we analyze the security of a
simple ensemble defense of CNNs and transformers. By creating a new attack, the
self-attention blended gradient attack, we show that such an ensemble is not
secure under a white-box adversary. However, under a black-box adversary, we
show that an ensemble can achieve unprecedented robustness without sacrificing
clean accuracy. Our analysis for this work is done using six types of white-box
attacks and two types of black-box attacks. Our study encompasses multiple
Vision Transformers, Big Transfer Models and CNN architectures trained on
CIFAR-10, CIFAR-100 and ImageNet
Towards an interpreter for efficient encrypted computation
Fully homomorphic encryption (FHE) techniques are capable of performing encrypted computation on Boolean circuits, i.e., the user specifies encrypted inputs to the program, and the server computes on the encrypted inputs. Applying these techniques to general programs with recursive procedures and data-dependent loops has not been a focus of attention. In this paper, we take a first step toward building an interpreter that, given programs with complex control flow, schedules efficient code suitable for the application of FHE schemes.
We first describe how programs written in a small Turing-complete instruction set can be executed with encrypted data and point out inefficiencies in this methodology. We then provide examples of scheduling (a) the greatest common divisor (GCD) problem using Euclid's algorithm and (b) the 3-Satisfiability (3SAT) problem using a recursive backtracking algorithm into path-levelized FHE computations. We describe how path levelization reduces control flow ambiguity and improves encrypted computation efficiency. Using these techniques and data-dependent loops as a starting point, we then build support for hierarchical programs made up of phases, where each phase corresponds to a fixed point computation that can be used to further improve the efficiency of encrypted computation.
In our setting, the adversary learns an estimate of the number of steps required to complete the computation, which we show is the least amount of leakage possible
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