27426921
Cryptographic logical relations
Using contextual equivalence (a.k.a. observational equivalence) to specify security properties is an important idea in the field of formal verification of cryptographic protocols. While contextual equivalence is difficult to prove directly, one is usually able to deduce it using the so-called logical relations in typed @l-calculi. We apply this technique to the cryptographic metalanguage-an extension of Moggi's computational @l-calculus, where we use Stark's model for name creation to explore the difficult aspect of dynamic key generation. The categorical construction of logical relations for monadic types (by Goubault-Larrecq et al.) then allows us to derive logical relations over the category Set^I. Although Set^I is a perfectly adequate model of dynamic key generation, it lacks in some aspects when we study relations between programs in the metalanguage. This leads us to an interesting exploration of what should be the proper category to consider. We show that, to define logical relations in the cryptographic metalanguage, a better choice of category is Set^I^^^-> that we proposed in [Y. Zhang, D. Nowak, Logical relations for dynamic name creation, in: Proceedings of the 17th International Workshop of Computer Science Logic and the 8th Kurt Godel Colloqium, CSL & KGL, in: Lecture Notes in Computer Science, vol. 2803, Springer-Verlag, 2003, pp. 575-588]. However, this category is still lacking in some subtler aspects and we propose a refined category Set^P^I^^^-> to fix the flaws, but our final choice is Set^I^x^I, which is equivalent to Set^P^I^^^->. We define the contextual equivalence based on Set^I^x^I and show that the cryptographic logical relation derived over Set^I^x^I is sound and can be used to verify protocols in practice.
1171092
On Completeness of Logical Relations for Monadic Types
Software security can be ensured by specifying and verifying security properties of software using formal methods with strong theoretical bases. In particular, programs can be modeled in the framework of lambda-calculi, and interesting properties can be expressed formally by contextual equivalence (a.k.a. observational equivalence). Furthermore, imperative features, which exist in most real-life software, can be nicely expressed in the so-called computational lambda-calculus. Contextual equivalence is difficult to prove directly, but we can often use logical relations as a tool to establish it in lambda-calculi. We have already defined logical relations for the computational lambda-calculus in previous work. We devote this paper to the study of their completeness w.r.t. contextual equivalence in the computational lambda-calculus.
21919804
Logical Relations for Dynamic Name Creation
Pitts and Stark’s nu-calculus is a typed lambda-calculus which forms a basis for the study of interaction between higher-order functions and dynamically created names. A similar approach has received renewed attention recently through Sumii and Pierce’s cryptographic lambda-calculus, which deals with security protocols. Logical relations are a powerful tool to prove properties of such a calculus, notably observational equivalence. While Pitts and Stark construct a logical relation for the nu-calculus, it rests heavily on operational aspects of the calculus and is hard to be extended. We propose an alternative Kripke logical relation for the nu-calculus, which is derived naturally from the categorical model of the nu-calculus and the general notion of Kripke logical relation. This is also related to the Kripke logical relation for the name creation monad by Goubault-Larrecq et al. (CSL’2002), which the authors claimed had similarities with Pitts and Stark’s logical relation. We show that their Kripke logical relation for names is strictly weaker than Pitts and Stark’s. We also show that our Kripke logical relation, which extends the definition of Goubault-Larrecq et al., is equivalent to Pitts and Stark’s up to first-order types; our definition rests on purely semantic constituents, and dispenses with the detours through operational semantics that Pitts and Stark use.
759478
A New Load Balancing Scheme for Distributed Multi-Agent Simulations
Disclosed is a heat sink clip assembly for releaseably attaching a heat sink to a DIP or similar electronic device package. The clip assembly includes a non-conductive attachment clip which extends between the leads on the underside of the DIP and means for latching the attachment clip to a heat sink disposed adjacent the opposite side of the electronic device package with the heat sink in intimate thermal contact with the electronic device package.
12359586
Verifying Anonymous Credential Systems in Applied Pi Calculus
Anonymous credentials are widely used to certify properties of a credential owner or to support the owner to demand valuable services, while hiding the user's identity at the same time. A credential system (a.k.a. pseudonym system) usually consists of multiple interactive procedures between users and organizations, including generating pseudonyms, issuing credentials and verifying credentials, which are required to meet various security properties. We propose a general symbolic model (based on the applied pi calculus) for anonymous credential systems and give formal definitions of a few important security properties, including pseudonym and credential unforgeability, credential safety, pseudonym untraceability. We specialize the general formalization and apply it to the verification of a concrete anonymous credential system proposed by Camenisch and Lysyanskaya. The analysis is done automatically with the tool ProVerif and several security properties have been verified.
10735385
Data-Driven Feature-Based 3D Face Synthesis
This paper presents a novel data-driven method for creating varied realistic face models by synthesizing a set of facial features according to intuitive high-level control parameters. Our method takes as examples 3D face scans in order to exploit the variations presented in the real faces of individuals. We use an automatic model fitting approach for the 3D registration problem. Once we have a common surface representation for each example, we form feature shape spaces by applying principal component analysis (PCA) to the data sets of facial feature shapes. Using PCA coefficients as a compact shape representation, we approach the shape synthesis problem by forming scattered data interpolation functions that are devoted to the generation of desired shape by taking the anthropometric parameters as input. The correspondence among all exemplar textures is obtained by parameterizing a 3D generic mesh over a 2D image domain. The new feature texture with desired attributes is synthesized by interpolating the example textures. Apart from an initial tuning of feature point positions and assignment of texture attribute values, our method is fully automated.
18837154
Inverting sensor networks and actuating the environment for spatio-temporal access control
Wireless sensor networks are typically deployed to measure the information field, rather than create an information field. However, by utilizing the radio on sensor nodes, it is possible to invert the role of sensor networks, and allow sensor nodes to actuate the environment. Such actuation can facilitate new forms of access control that are based on whether a user is located at the right place at the right time. In this paper, we explore the challenges of supporting spatio-temporal access control, where access to an object or service is based on the user's spatio-temporal context. Specifically, we focus on supporting spatio-temporal access control through the specification of access control policies, and show how complex spatio-temporal policies can be specified using automata. We outline a challenge-response mechanism for verifying user location in a centralized spatio-temporal access control mechanism. We utilize sensor networks in an inverted fashion to support spatio-temporal access control. Sensor nodes announce keys according to a time-varying schedule, and users may access restricted files/resources only if they are in the neighborhood of the correct sensor node and witness the appropriate cryptographic key.
35901095
The Computational SLR: A Logic for Reasoning about Computational Indistinguishability
Computational indistinguishability is a notion in complexity-theoretic cryptography and is used to define many security criteria. However, in traditional cryptography, proving computational indistinguishability is usually informal and becomes error-prone when cryptographic constructions are complex. This paper presents a formal proof system based on an extension of Hofmann's SLR language, which can capture probabilistic polynomial-time computations through typing and is sufficient for expressing cryptographic constructions. We in particular define rules that justify directly the computational indistinguishability between programs and prove that these rules are sound with respect to the set-theoretic semantics, hence the standard definition of security. We also show that it is applicable in cryptography by verifying, in our proof system, Goldreich and Micali's construction of pseudorandom generator.