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

Foundations, Properties, and Security Applications of Puzzles: A Survey

Cryptographic algorithms have been used not only to create robust ciphertexts but also to generate cryptograms that, contrary to the classic goal of cryptography, are meant to be broken. These cryptograms, generally called puzzles, require the use of a certain amount of resources to be solved, hence introducing a cost that is often regarded as a time delay---though it could involve other metrics as well, such as bandwidth. These powerful features have made puzzles the core of many security protocols, acquiring increasing importance in the IT security landscape. The concept of a puzzle has subsequently been extended to other types of schemes that do not use cryptographic functions, such as CAPTCHAs, which are used to discriminate humans from machines. Overall, puzzles have experienced a renewed interest with the advent of Bitcoin, which uses a CPU-intensive puzzle as proof of work. In this paper, we provide a comprehensive study of the most important puzzle construction schemes available in the literature, categorizing them according to several attributes, such as resource type, verification type, and applications. We have redefined the term puzzle by collecting and integrating the scattered notions used in different works, to cover all the existing applications. Moreover, we provide an overview of the possible applications, identifying key requirements and different design approaches. Finally, we highlight the features and limitations of each approach, providing a useful guide for the future development of new puzzle schemes.Comment: This article has been accepted for publication in ACM Computing Survey

Survey on: Software Puzzle for Offsetting DoS Attack

A Denial of Service (DoS) attack is a malevolent attempt to make a server or a network resource inaccessible to users, usually by temporarily breaking or suspending the services of a host connected to the Internet. DoS attacks and Distributed DoS (DDoS) attacks attempt to deplete an online service's resource such as network bandwidth, memory and computational power by overwhelming the service with bogus requests. Thus, DoS and DDoS attacks have become a major problem for users of computer systems connected to the Internet. Many state-art of the techniques used for defending the internet from these attacks have been discussed in this paper. After conducting an exhaustive survey on these techniques it has been found that the proposed software puzzle scheme that randomly generates only after a client request is received at the server side gives better performance as compared with previous techniques

A Novel WLAN Client Puzzle against DoS Attack Based on Pattern Matching

Despite the popularity of 802.11 based networks, they suffer several types of DoS attack, launched by an attacker whose aim is to make an access point (AP) unavailable to legitimate users. One of the most common DoS attacks on 802.11 based networks is to deplete the resources of the AP. A serious situation like this can occur when the AP receives a burst of connection requests. This paper addresses this common DoS attack and proposes a lightweight puzzle, based on pattern-matching. Using a pattern-matching technique, this model adequately resists resource-depletion attacks in terms of both puzzle generation and solution verification. Using a sensible series of contextual comparisons, the outcomes were modelled by a simulator, and the security definition and proofs are verified, among other results

Delegated Time-Lock Puzzle

Time-Lock Puzzles (TLPs) are cryptographic protocols that enable a client to lock a message in such a way that a server can only unlock it after a specific time period. However, existing TLPs have certain limitations: (i) they assume that both the client and server always possess sufficient computational resources and (ii) they solely focus on the lower time bound for finding a solution, disregarding the upper bound that guarantees a regular server can find a solution within a certain time frame. Additionally, existing TLPs designed to handle multiple puzzles either (a) entail high verification costs or (b) lack generality, requiring identical time intervals between consecutive solutions. To address these limitations, this paper introduces, for the first time, the concept of a "Delegated Time-Lock Puzzle" and presents a protocol called "Efficient Delegated Time-Lock Puzzle" (ED-TLP) that realises this concept. ED-TLP allows the client and server to delegate their resource-demanding tasks to third-party helpers. It facilitates real-time verification of solution correctness and efficiently handles multiple puzzles with varying time intervals. ED-TLP ensures the delivery of solutions within predefined time limits by incorporating both an upper bound and a fair payment algorithm. We have implemented ED-TLP and conducted a comprehensive analysis of its overheads, demonstrating the efficiency of the construction

Efficient trapdoor-based client puzzle system against DoS attacks

Denial of service (DoS) and distributed denial of service (DDoS) are serious threats to computer networks. DoS and DDoS attacks aim to shut down a target server by depleting its resources and rendering it incapable of offering stable and integrated service to legitimate clients. Preventing DoS and DDoS attacks is a difficult task. A promising countermeasure against DoS attacks is the Client Puzzle method, which nevertheless faces a number of challenges, such as the complexity of puzzle construction and solution verification. Our research focuses on exploring novel puzzle constructions to satisfy the high demands of DoS defence in practice. In this thesis, we first identify the underlying weaknesses of existing client puzzles. To mitigate these vulnerabilities, we recommend the necessary requirements for good client puzzles. Based on this, we propose a new model for puzzle distribution, called the Trapdoor-based Client Puzzle System (TCPS). Two specific schemes are presented to construct puzzles within TCPS. We depict these two schemes, where each trapdoor algorithm is applied respectively. Both schemes have two distinct features: the computational overheads are low, and the difficulty level of puzzles is measurable. Moreover, both puzzle schemes are provably secure under traditional hard problems in mathematics. Our contribution to client puzzle defence against DoS attacks can be summarised as follows: * Identify the shortcomings of existing client puzzles. * Recommend the requirements of good client puzzles. * Formally define the Trapdoor-based Client Puzzle System, along with strict security conditions. * Propose a client puzzle scheme whose security is based on the RSA Assumption. Effectiveness and security are analysed and proven. * Propose a second client puzzle scheme whose security is based on the Discrete Logarithm Problem (DLP). Similarly, effectiveness and security are also analysed. * Provide a possible configuration for system parameters. * Discuss further possible attacks and their solutions. As our research is carried out in DoS attack scenarios, we also introduce this technical background before our achievements are presented

Delegated Time-Lock Puzzle

Time-Lock puzzles (TLP) are cryptographic protocols that enable a client to lock a message in such a way that a server can only unlock it after a specific time period. However, existing TLPs have certain limitations: (i) they assume that both the client and server always possess sufficient computational resources and (ii) they solely focus on the lower time bound for finding a solution, disregarding the upper bound that guarantees a regular server can find a solution within a certain time frame. Additionally, existing TLPs designed to handle multiple puzzles either (a) entail high verification costs or (b) lack generality, requiring identical time intervals between consecutive solutions. To address these limitations, this paper introduces, for the first time, the concept of a Delegated Time-Lock Puzzle and presents a protocol called Efficient Delegated Time- Lock Puzzle (ED-TLP) that realises this concept. ED-TLP allows the client and server to delegate their resource-demanding tasks to third-party helpers. It facilitates real-time verification of solution correctness and efficiently handles multiple puzzles with varying time intervals. ED-TLP ensures the delivery of solutions within predefined time limits by incorporating both an upper bound and a fair payment algorithm. We have implemented ED-TLP and conducted a comprehensive analysis of its overheads, demonstrating the efficiency of the constructio

Multi-instance publicly verifiable time-lock puzzle and its applications

Time-lock puzzles are elegant protocols that enable a party to lock a message such that no one else can unlock it until a certain time elapses. Nevertheless, existing schemes are not suitable for the case where a server is given multiple instances of a puzzle scheme at once and it must unlock them at different points in time. If the schemes are naively used in this setting, then the server has to start solving all puzzles as soon as it receives them, that ultimately imposes significant computation cost and demands a high level of parallelisation. We put forth and formally define a primitive called “multi-instance time-lock puzzle” which allows composing a puzzle’s instances. We propose a candidate construction: “chained time-lock puzzle” (C-TLP). It allows the server, given instances’ composition, to solve puzzles sequentially, without having to run parallel computations on them. C-TLP makes black-box use of a standard time-lock puzzle scheme and is accompanied by a lightweight publicly verifiable algorithm. It is the first time-lock puzzle that offers a combination of the above features. We use C-TLP to build the first “outsourced proofs of retrievability” that can support real-time detection and fair payment while having lower overhead than the state of the art. As another application of C-TLP, we illustrate in certain cases, one can substitute a “verifiabledelay function” with C-TLP, to gain much better efficiency

Verifiable Delay Functions

We study the problem of building a verifiable delay function (VDF). A VDF requires a specified number of sequential steps to evaluate, yet produces a unique output that can be efficiently and publicly verified. VDFs have many applications in decentralized systems, including public randomness beacons, leader election in consensus protocols, and proofs of replication. We formalize the requirements for VDFs and present new candidate constructions that are the first to achieve an exponential gap between evaluation and verification time