Denial-of-Service Resistance in Key Establishment

Denial of Service (DoS) attacks are an increasing problem for network connected systems. Key establishment protocols are applications that are particularly vulnerable to DoS attack as they are typically required to perform computationally expensive cryptographic operations in order to authenticate the protocol initiator and to generate the cryptographic keying material that will subsequently be used to secure the communications between initiator and responder. The goal of DoS resistance in key establishment protocols is to ensure that attackers cannot prevent a legitimate initiator and responder deriving cryptographic keys without expending resources beyond a responder-determined threshold. In this work we review the strategies and techniques used to improve resistance to DoS attacks. Three key establishment protocols implementing DoS resistance techniques are critically reviewed and the impact of misapplication of the techniques on DoS resistance is discussed. Recommendations on effectively applying resistance techniques to key establishment protocols are made

Protocol engineering for protection against denial-of-service attacks

Denial-of-service attacks (DoS) and distributed denial-of-service attacks (DDoS) attempt to temporarily disrupt users or computer resources to cause service un- availability to legitimate users in the internetworking system. The most common type of DoS attack occurs when adversaries °ood a large amount of bogus data to interfere or disrupt the service on the server. The attack can be either a single-source attack, which originates at only one host, or a multi-source attack, in which multiple hosts coordinate to °ood a large number of packets to the server. Cryptographic mechanisms in authentication schemes are an example ap- proach to help the server to validate malicious tra±c. Since authentication in key establishment protocols requires the veri¯er to spend some resources before successfully detecting the bogus messages, adversaries might be able to exploit this °aw to mount an attack to overwhelm the server resources. The attacker is able to perform this kind of attack because many key establishment protocols incorporate strong authentication at the beginning phase before they can iden- tify the attacks. This is an example of DoS threats in most key establishment protocols because they have been implemented to support con¯dentiality and data integrity, but do not carefully consider other security objectives, such as availability. The main objective of this research is to design denial-of-service resistant mechanisms in key establishment protocols. In particular, we focus on the design of cryptographic protocols related to key establishment protocols that implement client puzzles to protect the server against resource exhaustion attacks. Another objective is to extend formal analysis techniques to include DoS- resistance. Basically, the formal analysis approach is used not only to analyse and verify the security of a cryptographic scheme carefully but also to help in the design stage of new protocols with a high level of security guarantee. In this research, we focus on an analysis technique of Meadows' cost-based framework, and we implement DoS-resistant model using Coloured Petri Nets. Meadows' cost-based framework is directly proposed to assess denial-of-service vulnerabil- ities in the cryptographic protocols using mathematical proof, while Coloured Petri Nets is used to model and verify the communication protocols using inter- active simulations. In addition, Coloured Petri Nets are able to help the protocol designer to clarify and reduce some inconsistency of the protocol speci¯cation. Therefore, the second objective of this research is to explore vulnerabilities in existing DoS-resistant protocols, as well as extend a formal analysis approach to our new framework for improving DoS-resistance and evaluating the performance of the new proposed mechanism. In summary, the speci¯c outcomes of this research include following results; 1. A taxonomy of denial-of-service resistant strategies and techniques used in key establishment protocols; 2. A critical analysis of existing DoS-resistant key exchange and key estab- lishment protocols; 3. An implementation of Meadows's cost-based framework using Coloured Petri Nets for modelling and evaluating DoS-resistant protocols; and 4. A development of new e±cient and practical DoS-resistant mechanisms to improve the resistance to denial-of-service attacks in key establishment protocols

Toward Non-Parallelizable Client Puzzles

Client puzzles have been proposed as a useful mechanism for mitigating denial of service attacks on network protocols. Several different puzzles have been proposed in recent years. This paper reviews the desirable properties of client puzzles, pointing out that there is currently no puzzle which satisfies all such properties. We investigate how to provide the property of non-parallelizability in a practical puzzle. After showing that obvious ideas based on hash chains have significant problems, we propose a new puzzle based on the subset sum problem. Despite some practical implementation issues, this is the first example that satisfies all the desirable properties for a client puzzle

Examining the DOS Resistance to HIP

We examine DoS resistance of the Host Identity Protocol (HIP) and discuss a technique to deny legitimate services. To demonstrate the experiment, we implement a formal model of HIP based on Timed Petri Nets and use a simulation approach provided in CPN Tools to achieve a formal analysis. By integrating adjustable puzzle difficulty, HIP can mitigate the effect of DoS attacks. However, the inability to protect against coordinated adversaries on a hash-based puzzle causes the responder to be susceptible to DoS attacks at the identity verification phase. As a result, we propose an enhanced approach by employing a time-lock puzzle instead of a hash-based scheme. Once the time-lock puzzle is adopted, the effect of coordinated attacks will be removed and the throughput from legitimate users will return to the desirable level

Cost-Based and Time-Based Analysis of DoS-Resistance in HIP

We develop a formal model of the Host Identity Protocol (HIP) based on Timed Coloured Petri Nets (Timed CPNs) and use a simulation approach provided in CPN Tools to achieve a formal analysis. We aim to examine unbalanced computation that leads to resource exhaustion attacks in key exchange protocols comparing among a legitimate initiator, four types of adversary who attempt to deny the service at different stages of the protocol execution, and a responder. By adopting the key idea of Meadows' cost-based framework and refining the definition of operational costs during the protocol execution, our simulation provides an accurate cost estimate of protocol execution comparing between those principals. Under four defined attack strategies, however, Meadows' cost-based framework generates a different outcome compared with the simulation approach from Timed CPNs. Analysis of our experimental results reveals a limitation of Meadows' cost-based framework for addressing DoS threats

Using Coloured Petri Nets to Simulate DoS-resistant Protocols

In this work, we examine unbalanced computation between an initiator and a responder that leads to resource exhaustion attacks in key exchange protocols. We construct models for two cryp-tographic protocols; one is the well-known Internet protocol named Secure Socket Layer (SSL) protocol, and the other one is the Host Identity Protocol (HIP) which has built-in DoS-resistant mechanisms. To examine such protocols, we develop a formal framework based on Timed Coloured Petri Nets (Timed CPNs) and use a simulation approach provided in CPN Tools to achieve a formal analysis. By adopting the key idea of Meadows' cost-based framework and re¯ning the de¯nition of operational costs during the protocol execution, our simulation provides an accurate cost estimate of protocol execution compar- ing among principals, as well as the percentage of successful connections from legitimate users, under four di®erent strategies of DoS attack