Iakovos Ouranos

A radio-coverage prediction model in wireless communication systems based on physical optics and the physical theory of diffraction [Wireless Corner]

In this paper, a two-dimensional (2D) simulation method for the calculation of radio coverage in urban-area sites is presented, based on the analytical methods of physical optics (PO) and the physical theory of diffraction (PTD). The method takes into account the electromagnetic field at the receiving antenna due to first- and higher-order propagation mechanisms. Emphasis is given on the computation of the scattered near or Fresnel-zone field using numerical techniques, since in a typical urban environment, the scattered near or Fresnel-zone field occupies a large percentage of the area under investigation. The high resolution radio-coverage plots are computed by complex vector addition of all of the received signals for several values of the channel parameters. Finally, a comparison of the radio-coverage results obtained through this method with the corresponding results based on different electromagnetic methods and measurements, previously published in the literature, is presented.

Formal analysis of TESLA protocol in the timed OTS/CafeOBJ method

The Timed Observational Transition System (TOTS)/CafeOBJ method is a version of the OTS/CafeOBJ method for modeling, specification and verification of distributed systems and protocols with real time constraints. In this paper we report on a case study from the field of source authentication protocols, TESLA protocol, to show the application of the method to such complex systems. We prove that our model of the protocol satisfies that the receiver does not accept as authentic any message unless it was actually sent by the sender. To verify the property we have used several other invariants which include timing information. To our knowledge, this is the first time that the method has been applied to the formal analysis of such a complex protocol.

Algebraic Specifications for OMA REL Licenses

OMA-Digital Rights Management System is a standard proposed by Open Mobile Alliance for protecting digital content distributed through mobile networks. In such a system, licenses are written in an appropriate language and used to ensure the fine grained consumption of contents. We claim that the Rights Expression Language (OMA-REL) does not rely on formal semantics. To address this problem we propose an abstract syntax for OMA-REL and write an algebraic specification of it using CafeOBJ, an executable algebraic specification language, with the future goal the creation of automated tools that check the behavior of a set of licenses under a certain environment.

Scattering of Electromagnetic Waves From a Rectangular Plate Using an Enhanced Stationary Phase Method Approximation

A time-efficient high frequency analytical model for the calculation of the scattered field from a perfect electric conductor (PEC) plate is presented here, which is based on the physical optics (PO) approximation and the stationary phase method (SPM). Using the SPM analysis for the three-dimensional (3D) scattering problem under consideration, the scattered electric field is calculated analytically. It follows that the analytical formula proposed here yields an accurate and fast algorithm for the calculation of the scattered electromagnetic (EM) field, which can be used trustfully in a variety of radio propagation problems. The accuracy of the proposed analytical method is checked through a straightforward numerical integration over the PO currents, as well as through finite element boundary integral full-wave exact solution. Comparison results are given in the far field, Fresnel zone and the near field area.

Verifying security protocols for sensor networks using algebraic specification techniques

Algebraic specification languages are formal methods that provide a rigorous basis for modeling of several systems. Security protocols are safety critical systems that need to be verified before their implementation. In this paper we have formally specified sensor network encryption protocol (SNEP) and a key agreement protocol for sensor networks, both from the SPINS protocol suite, with the OTS/CafeOBJ method, a well known formal specification technique applied not only in research, but also in industry. Based on this specification, we have proved that each protocol possesses an important safety(invariant) property.

Formal modeling and verification of sensor network encryption protocol in the OTS/CafeOBJ method

Sensor Network Encryption Protocol (SNEP) is one of the secure building blocks of the SPINS Protocol Suite and provides data confidentiality, two-party data authentication and evidence of data freshness in a wireless sensor network. We have formally analyzed SNEP and a node-to-node key agreement protocol based on it, using the OTS/CafeOBJ method. Among other invariants, we have verified that the protocols possess the important security properties of authenticity and confidentiality of relevant message components. To our knowledge, we are the first to formally analyze SNEP using algebraic specification techniques.

An Algebraic Specification for the MPEG-2 Encoding Algorithm

The MPEG-2 encoding algorithm is a compression tool for moving pictures and associated audio, developed by the Moving Picture Experts Group (MPEG) and is designed to cover a wide range of requirements from “VHS quality” to“HDTV”. The compression methods used by MPEG-2 are considered to be asymmetrical in the meaning that the encoder is more complex than the decoder. This approach is new because MPEG does not specify the whole encoding process. In fact, the most important step of the encoding algorithm (namely the algorithms used to produce the motion vector) is not specified. Only some basic steps and the format of the compatible output are explicit specified, so that each encoder provider can create his own interpretation of the algorithm. This technique has the benefit that the decoders will remain compatible even as the encoders evolve. Due to its high acceptance and wide use, it is important to verify that the algorithm works as expected using formal methods, not only testing. To this end, we have used CafeOBJ, an executable algebraic specification language, to specify the algorithm and prove some desirable safety properties. More precisely, we specified the MPEG-2 encoding algorithm, considering the unspecified by MPEG steps as black boxes, as an Observational Transition System in CafeOBJ, and created a formal proof that for any input the output is as expected, thus proving that the algorithm works correctly.

Radio coverage prediction method in urban microcellular environment using electromagnetic techniques

A simulation method for the calculation of the radio propagation in urban area, sites is presented, based on analytical electromagnetic techniques. First of all we summarize the basic theory of physical optics (PO) and physical theory of diffraction (PTD) for the definition of first and second order reflected and diffracted fields in the far field area. We are also presenting formulas that calculate either numerically or analytically the near scattered electric field, because in a typical urban environment the scattered near field from walls occupies a large percentage of the area. Near field simulation results which are either in the form of potential coefficients or electric field vector appear for various data, inputs, resulting in a more accurate calculation of the electric field near the scattered surfaces

From ASN.1 into CafeOBJ: Some First Steps

Abstract Syntax Notation One (ASN.1) is a very popular specification language with many applications in networking. We work towards the correct translation from ASN.1, into the powerful algebraic specification language CafeOBJ. Our aim is to create a software environment that can translate correctly a protocols specification written in ASN.1 into the powerful algebraic specification language CafeOBJ. We believe that such an environment would be a step towards the adoption of algebraic specification methodologies from the networking research community. This formal translation will allow the verification of system-critical properties of the designed protocol at the pre-coding stage of development. The software environment will make full use of the huge ASN.1 specification library and the powerful proving engine of CafeOBJ. In our paper we first introduce the key elements of both ASN.1 and CafeOBJ, and then we sketch our proposed translation rules and suggest a methodology for proving correctness. Finally, as a case study we translate an ASN.1 specification of a basic banking system into CafeOBJ and then use the resulting modules to find and verify some system-critical properties.

Towards a Protocol Algebra Based on Algebraic Specifications

We sketch some first steps towards the definition of a protocol algebra based on the framework of behavioural algebraic specification. Following the tradition of representing protocols as state machines, we use the notion of Observational Transition System to express them in an executable algebraic specification language such as CafeOBJ. This abstract approach allows defining several useful operators for protocol reasoning and proving properties of them using theorem proving techniques and CafeOBJ term rewriting machine. The proposed protocol algebra is inspired by the module algebra and the hierarchical object composition technique.