1,445 research outputs found
A Symbolic Intruder Model for Hash-Collision Attacks
In the recent years, several practical methods have been published to compute
collisions on some commonly used hash functions. In this paper we present a
method to take into account, at the symbolic level, that an intruder actively
attacking a protocol execution may use these collision algorithms in reasonable
time during the attack. Our decision procedure relies on the reduction of
constraint solving for an intruder exploiting the collision properties of hush
functions to constraint solving for an intruder operating on words
Finitary Deduction Systems
Cryptographic protocols are the cornerstone of security in distributed
systems. The formal analysis of their properties is accordingly one of the
focus points of the security community, and is usually split among two groups.
In the first group, one focuses on trace-based security properties such as
confidentiality and authentication, and provides decision procedures for the
existence of attacks for an on-line attackers. In the second group, one focuses
on equivalence properties such as privacy and guessing attacks, and provides
decision procedures for the existence of attacks for an offline attacker. In
all cases the attacker is modeled by a deduction system in which his possible
actions are expressed. We present in this paper a notion of finitary deduction
systems that aims at relating both approaches. We prove that for such deduction
systems, deciding equivalence properties for on-line attackers can be reduced
to deciding reachability properties in the same setting.Comment: 30 pages. Work begun while in the CASSIS Project, INRIA Nancy Grand
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YAPA: A generic tool for computing intruder knowledge
Reasoning about the knowledge of an attacker is a necessary step in many
formal analyses of security protocols. In the framework of the applied pi
calculus, as in similar languages based on equational logics, knowledge is
typically expressed by two relations: deducibility and static equivalence.
Several decision procedures have been proposed for these relations under a
variety of equational theories. However, each theory has its particular
algorithm, and none has been implemented so far. We provide a generic procedure
for deducibility and static equivalence that takes as input any convergent
rewrite system. We show that our algorithm covers most of the existing decision
procedures for convergent theories. We also provide an efficient
implementation, and compare it briefly with the tools ProVerif and KiSs
Unification modulo a 2-sorted Equational theory for Cipher-Decipher Block Chaining
We investigate unification problems related to the Cipher Block Chaining
(CBC) mode of encryption. We first model chaining in terms of a simple,
convergent, rewrite system over a signature with two disjoint sorts: list and
element. By interpreting a particular symbol of this signature suitably, the
rewrite system can model several practical situations of interest. An inference
procedure is presented for deciding the unification problem modulo this rewrite
system. The procedure is modular in the following sense: any given problem is
handled by a system of `list-inferences', and the set of equations thus derived
between the element-terms of the problem is then handed over to any
(`black-box') procedure which is complete for solving these element-equations.
An example of application of this unification procedure is given, as attack
detection on a Needham-Schroeder like protocol, employing the CBC encryption
mode based on the associative-commutative (AC) operator XOR. The 2-sorted
convergent rewrite system is then extended into one that fully captures a block
chaining encryption-decryption mode at an abstract level, using no AC-symbols;
and unification modulo this extended system is also shown to be decidable.Comment: 26 page
Development of security strategies using Kerberos in wireless networks
Authentication is the primary function used to reduce the risk of illegitimate access to IT services of any organisation. Kerberos is a widely used authentication protocol for authentication and access control mechanisms.
This thesis presents the development of security strategies using Kerberos authentication protocol in wireless networks, Kerberos-Key Exchange protocol, Kerberos with timed-delay, Kerberos with timed-delay and delayed decryption, Kerberos with timed-delay, delayed decryption and password encryption properties. This thesis also includes a number of other research works such as, frequently key renewal under pseudo-secure conditions and shut down of the authentication server to external access temporarily to allow for secure key exchange.
A general approach for the analysis and verification of authentication properties as well as Kerberos authentication protocol are presented. Existing authentication mechanisms coupled with strong encryption techniques are considered, investigated and analysed in detail. IEEE 802.1x standard, IEEE 802.11 wireless communication networks are also considered. First, existing security and authentication approaches for Kerberos authentication protocol are critically analysed with the discussions on merits and weaknesses. Then relevant terminology is defined and explained.
Since Kerberos exhibits some vulnerabilities, the existing solutions have not treated the possibilities of more than one authentication server in a strict sense. A three way authentication mechanism addresses possible solution to this problem. An authentication protocol has been developed to improve the three way authentication mechanism for Kerberos. Dynamically renewing keys under pseudo-secure situations involves a temporary interruption to link/server access. After describing and analysing a protocol to achieve improved security for authentication, an analytical method is used to evaluate the cost in terms of the degradation of system performability. Various results are presented.
An approach that involves a new authentication protocol is proposed. This new approach combines delaying decryption with timed authentication by using passwords and session keys for authentication purposes, and frequent key renewal under secure conditions. The analysis and verification of authentication properties and results of the designed protocol are presented and discussed.
Protocols often fail when they are analysed critically. Formal approaches have emerged to analyse protocol failures. Abstract languages are designed especially for the description of communication patterns. A notion of rank functions is introduced for analysing purposes as well. An application of this formal approach to a newly designed authentication protocol that combines delaying the decryption process with timed authentication is presented.
Formal methods for verifying cryptographic protocols are created to assist in ensuring that authentication protocols meet their specifications. Model checking techniques such as Communicating Sequential Processes (CSP) and Failure Divergence Refinement (FDR) checker, are widely acknowledged for effectively and efficiently revealing flaws in protocols faster than most other contemporaries. Essentially, model checking involves a detailed search of all the states reachable by the components of a protocol model. In the models that describe authentication protocols, the components, regarded as processes, are the principals including intruder (attacker) and parameters for authentication such as keys, nonces, tickets, and certificates. In this research, an automated generation tool, CASPER is used to produce CSP descriptions. Proposed protocol models rely on trusted third parties in authentication transactions while intruder capabilities are based on possible inductions and deductions. This research attempts to combine the two methods in model checking in order to realise an abstract description of intruder with enhanced capabilities. A target protocol of interest is that of Kerberos authentication protocol.
The process of increasing the strength of security mechanisms usually impacts on performance thresholds. In recognition of this fact, the research adopts an analytical method known as spectral expansion to ascertain the level of impact, and which resulting protocol amendments will have on performance. Spectral expansion is based on state exploration. This implies that it is subject, as model checking, to the state explosion problem. The performance characteristics of amended protocols are examined relative to the existing protocols.
Numerical solutions are presented for all models developed
Hierarchical combination of intruder theories
International audienceRecently automated deduction tools have proved to be very effective for detecting attacks on cryptographic protocols. These analysis can be improved, for finding more subtle weaknesses, by a more accurate modelling of operators employed by protocols. Several works have shown how to handle a single algebraic operator (associated with a fixed intruder theory) or how to combine several operators satisfying disjoint theories. However several interesting equational theories, such as exponentiation with an abelian group law for exponents remain out of the scope of these techniques. This has motivated us to introduce a new notion of hierarchical combination for non-disjoint intruder theories and to show decidability results for the deduction problem in these theories. We have also shown that under natural hypotheses hierarchical intruder constraints can be decided. This result applies to an exponentiation theory that appears to be more general than the one considered before
Satisfiability of General Intruder Constraints with and without a Set Constructor
Many decision problems on security protocols can be reduced to solving
so-called intruder constraints in Dolev Yao model. Most constraint solving
procedures for protocol security rely on two properties of constraint systems
called monotonicity and variable origination. In this work we relax these
restrictions by giving a decision procedure for solving general intruder
constraints (that do not have these properties) that stays in NP. Our result
extends a first work by L. Mazar\'e in several directions: we allow non-atomic
keys, and an associative, commutative and idempotent symbol (for modeling
sets). We also discuss several new applications of the results.Comment: Submitted to the Special issue of Information and Computation on
Security and Rewriting Techniques (SecReT), 2011. 59 page
Information Structures with Unawareness
I construct a state space model with unawareness following Aumann (1976). Dekel, Lipman and Rustichini (1998a) show that standard state space models are incapable of representing unawareness. The model circumvents the impossibility result by endowing the agent with a subjective state space that differs from the full state space when he has the unawareness problem. Information is modeled as a pair, consisting of both factual information and awareness information. The model preserves the central properties of the standard information partition model.unawareness, information, information partition, state space models
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