Finite Number Of Sessions Research Articles

Protocol insecurity with a finite number of sessions and a cost-sensitive guessing intruder is NP-complete

Guessing attacks in security protocols arise when honest agents make use of data easily guessable by an intruder, such as passwords generated from a small dictionary. A way to model such attacks is to formalize a Dolev–Yao style model with inference rules that capture the additional capabilities of the intruder concerning guessable data. In this paper, we formalize a cost-sensitive intruder deduction system where information is available at a cost. The intruder may apply standard operations to deduce new messages from his current knowledge, or invoke an oracle rule that allows him to get hold of data that was previously unknown to him. Our system manipulates data items by means of inference rules and uses labels to keep track of the costs associated to the application of each rule. This allows us to answer the question of what is the cost of deducing a particular data that was meant to remain a secret between honest protocol participants. We also investigate the complexity of this quantitative insecurity problem and show that it is NP-complete in the case of a finite number of protocol sessions.

Timed protocol insecurity problem is NP-complete

In this paper we study the protocol insecurity problem for time-dependent security protocols under the finite number of sessions’ assumption, extending to the timed case, previous results obtained for the same problem in the untimed case. In particular, we propose a timed specification language, which allows to model temporal features typically involved in the implementation of security protocols. We introduce a stronger version of the Dolev–Yao intruder, by allowing it to generate new timestamps which can affect the execution of a protocol sensitive to their temporal validity. We prove that this temporal extension together with the increased power of the intruder model do not affect the complexity of the protocol insecurity problem, which remains NP-complete as in the untimed case.

On the Effect of a Random Access Protocol on the Performance of the Session-Based Data Subsystem in GSM/GPRS

Research into mixed services in mobile cellular networks is highly topical. Session-based applications (e.g., Web browsing) form significant and increasing data traffic in cellular networks. In such mixed services, random access (RA) protocols impose significant effects in performance metrics of the new data users. To date, analytical facility has been limited by the absence of closed-form models for the RA protocols that exist in time-division multiple access (TDMA) cellular networks with mixed voice (as circuit switched) and data with finite number of sessions (as packet switched). In this novel paper, we research an RA protocol based on S-Aloha with data as a session for mobile TDMA cellular networks and present an analytical framework. This work is germane to Global System for Mobile Communications/General Packet Radio Service systems. This paper begins with a general model description of a voice and data subsystem, and an explanation of its admission schemes. As well as the model, an analytical framework based on equilibrium point analysis is derived, and an algorithm is then formulated to complement the analytical framework. Using this novel analytical framework, together with the associated algorithm, performance metrics of the system such as throughput, mean access delay, and mean delay in the queue are obtained. Stability conditions are also highlighted. Numerical results are corroborated using simulation.

An NP decision procedure for protocol insecurity with XOR

We provide a method for deciding the insecurity of cryptographic protocols in the presence of the standard Dolev-Yao intruder (with a finite number of sessions) extended with so-called oracle rules, i.e., deduction rules that satisfy certain conditions. As an instance of this general framework, we obtain that protocol insecurity is in NP for an intruder that can exploit the properties of the exclusive or (XOR) operator. This operator is frequently used in cryptographic protocols but cannot be handled in most protocol models. An immediate consequence of our proof is that checking whether a message can be derived by an intruder (using XOR) is in PTIME. We also apply our framework to an intruder that exploits properties of certain encryption modes such as cipher block chaining (CBC).

Performance analysis of integrated voice and multiple classes of data with a finite number of sessions

AbstractThis paper discusses a TDM multi‐access channel that supports hybrid switching including circuit switched voice and packet switched data as KC classes with a finite number of open sessions. The channel is partitioned into KC sub‐channels that are assigned to classes. Applications are hybrid switching in mobile TDMA (e.g. GSM/GPRS cellular networks) and time division multiplexing systems. Herein, an original analysis for such mixed services is derived. In this paper, a new Markov model for voice traffic in each sub‐channel is shown. The system is modelled with an irreducible continuous time and aperiodic Markov process and a non‐homogenous finite QBD process based on macrostructure model of TDM channel is derived. A novel computational algorithm is then formulated. Using the computational algorithm, performance metrics of the system such as mean delay in the queue as well as average number of data users in queue will be obtained. QoS is defined and the advantage of channel sharing is highlighted. Numerical results are corroborated by simulation. Copyright © 2004 AEI

Analysis of security protocols as open systems

We propose a methodology for the formal analysis of security protocols. This originates from the observation that the verification of security protocols can be conveniently treated as the verification of open systems, i.e. systems which may have unspecified components. These might be used to represent a hostile environment wherein the protocol runs and whose behavior cannot be predicted a priori. We define a language for the description of security protocols, namely Crypto-CCS, and a logical language for expressing their properties. We provide an effective verification method for security protocols which is based on a suitable extension of partial model checking. Indeed, we obtain a decidability result for the secrecy analysis of protocols with a finite number of sessions, bounded message size and new nonce generation.

How to Practice Brief Psychodynamic Psychotherapy: The Core Conflictual Relationship Theme Method

Back to table of contents Previous article Next article Book ReviewFull AccessHow to Practice Brief Psychodynamic Psychotherapy: The Core Conflictual Relationship Theme MethodRobert Andre Kimmich, M.D.Robert Andre KimmichSearch for more papers by this author, M.D.Published Online:1 Aug 1999https://doi.org/10.1176/ps.50.8.1095AboutSectionsView EPUB ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail This slim volume should be read by every professional who practices psychotherapy. The importance of the work lies in its intimate style and inside view of the psychotherapeutic dyad. One feels as if in the presence of a wise and skilled psychiatrist who is talking about his work to a fellow colleague, the reader. Dr. Book does not preach or harangue, but elucidates the therapeutic interchange. Although the author calls his book a manual, its strength lies in his clarification of why treatment in his hands proceeds the way it does.Dr. Book is an associate professor of psychiatry at the University of Toronto Faculty of Medicine and is also in private practice. He has specialized in developing and teaching brief psychodynamic psychotherapy. His text is intended as a practical, step-by-step manual for teaching therapists of various disciplines the core conflictual relationship theme (CCRT) method of brief psychotherapy developed by Lester Luborsky, Ph.D., and others.The introductory chapter consists of 18 pages of an outstanding summary of principles of psychodynamic psychotherapy. It can apply to any school of dynamic therapy. It takes an expert to boil down so much important material into a readable and concise form. Readers should not skip this section.The CCRT method is set forth in detail in part 1. The author states the goals as follows: "Brief psychodynamic psychotherapy has as its goals symptom relief and limited, though significant, character change attained through a finite number of sessions." He goes on to say, "As with all dynamic psychotherapies, including long-term psychotherapy and psychoanalysis, the practice of brief psychodynamic psychotherapy requires the therapist to blend expressive and supportive activities."Dr. Book explains that patients need to be suited to the method, with adequate ego strength and verbal ability, and must able to work within the weekly, 16-session format specified for CCRT. The 16-session limit is not carved in granite but provides the chronological and technical context. The author discusses when and how to deviate from the time limit.A major component of the method is to choose one specific, important, repetitive conflictual relationship problem on which to focus treatment. The therapist conceptualizes this problem after a thorough evaluation and formulation.Part 1 also deals with developing the focus of the CCRT, or the theme of the brief psychodynamic therapy. Even though the details are common sense to an experienced therapist, it is fascinating to follow Dr. Book's treatment examples as they unfold. They are complete with commentary, including discussion of transference and countertransference and repetition compulsion. I was a little put off by the codification of conflict components—for instance, RO for response from the other, RE for relationship episode, W for wish, and RS for response from the staff—but one catches on. The ideas are quite useful.Part 2 is the engaging verbatim transcription of a course of therapy with one of the author's patients. Dr. Book treats us to his own running commentary to the transcription, in an engrossing discussion of the technical hows and whys. It is hard to put this excellent book down.How to Practice Brief Psychodynamic Psychotherapy will be interesting reading for the trained and accomplished psychotherapist, but also of great value to the advanced trainee who has some basic knowledge of psychodynamic concepts. Another audience for this fine exposition would be psychiatric residency training directors or other advanced professionals in psychotherapy training programs.Dr. Book does a masterful job of meeting the objectives of this work and certainly demonstrates his own skill in the process. Useful references are also supplied. Even though he sets out to provide a manual on brief psychodynamic psychotherapy, he succeeds more broadly in emphasizing skills needed for psychotherapy of any duration.Dr. Kimmich is in the private practice of psychiatry in San Francisco and is a member of the American Psychiatric Association's commission on psychotherapy by psychiatrists.by Howard E. Book, M.D., D.Psych.; Washington, D.C., American Psychological Association, 1998, 181 pages, $39.95 FiguresReferencesCited byDetailsCited ByNone Volume 50Issue 8 August 1999Pages 1095-1096 Metrics History Published online 1 August 1999 Published in print 1 August 1999