Systemization of Pluggable Transports for Censorship Resistance

An increasing number of countries implement Internet censorship at different scales and for a variety of reasons. In particular, the link between the censored client and entry point to the uncensored network is a frequent target of censorship due to the ease with which a nation-state censor can control it. A number of censorship resistance systems have been developed thus far to help circumvent blocking on this link, which we refer to as link circumvention systems (LCs). The variety and profusion of attack vectors available to a censor has led to an arms race, leading to a dramatic speed of evolution of LCs. Despite their inherent complexity and the breadth of work in this area, there is no systematic way to evaluate link circumvention systems and compare them against each other. In this paper, we (i) sketch an attack model to comprehensively explore a censor's capabilities, (ii) present an abstract model of a LC, a system that helps a censored client communicate with a server over the Internet while resisting censorship, (iii) describe an evaluation stack that underscores a layered approach to evaluate LCs, and (iv) systemize and evaluate existing censorship resistance systems that provide link circumvention. We highlight open challenges in the evaluation and development of LCs and discuss possible mitigations.Comment: Content from this paper was published in Proceedings on Privacy Enhancing Technologies (PoPETS), Volume 2016, Issue 4 (July 2016) as "SoK: Making Sense of Censorship Resistance Systems" by Sheharbano Khattak, Tariq Elahi, Laurent Simon, Colleen M. Swanson, Steven J. Murdoch and Ian Goldberg (DOI 10.1515/popets-2016-0028

Where public interest and public benefit meet: the application of charity law to journalism

Under-investment in public service journalism has led to growing interest in the possibility of philanthropic support for the sector. Though long associated with non-profit journalism in North America, there is little tradition of philanthropy in UK journalism. This paper explains how recognition of public interest journalism as charitable can be achieved through more constructive interpretations of the existing law. Despite its initially conservative response, the Charity Commission has recently taken important steps towards recognising defined forms of journalism as charitable under the existing law. This paper reviews the democratic imperatives fulfilled by public interest journalism which justify such developments; and seeks to demonstrate how this framework for defining public interest journalism aligns with the public benefit requirement in charity law, opening up the possibility of new forms of charitably funded ‘public benefit journalism’

EMV: Why Payment Systems Fail

What lessons might we learn from the chip cards used for payments in Europe, now that the U.S. is adopting them too?</jats:p

Chip and Skim: cloning EMV cards with the pre-play attack

EMV, also known as "Chip and PIN", is the leading system for card payments worldwide. It is used throughout Europe and much of Asia, and is starting to be introduced in North America too. Payment cards contain a chip so they can execute an authentication protocol. This protocol requires point-of-sale (POS) terminals or ATMs to generate a nonce, called the unpredictable number, for each transaction to ensure it is fresh. We have discovered that some EMV implementers have merely used counters, timestamps or home-grown algorithms to supply this number. This exposes them to a "pre-play" attack which is indistinguishable from card cloning from the standpoint of the logs available to the card-issuing bank, and can be carried out even if it is impossible to clone a card physically (in the sense of extracting the key material and loading it into another card). Card cloning is the very type of fraud that EMV was supposed to prevent. We describe how we detected the vulnerability, a survey methodology we developed to chart the scope of the weakness, evidence from ATM and terminal experiments in the field, and our implementation of proof-of-concept attacks. We found flaws in widely-used ATMs from the largest manufacturers. We can now explain at least some of the increasing number of frauds in which victims are refused refunds by banks which claim that EMV cards cannot be cloned and that a customer involved in a dispute must therefore be mistaken or complicit. Pre-play attacks may also be carried out by malware in an ATM or POS terminal, or by a man-in-the-middle between the terminal and the acquirer. We explore the design and implementation mistakes that enabled the flaw to evade detection until now: shortcomings of the EMV specification, of the EMV kernel certification process, of implementation testing, formal analysis, or monitoring customer complaints. Finally we discuss countermeasures

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

Recurring Contingent Service Payment

Fair exchange protocols let two mutually distrustful parties exchange digital data in a way that neither party can cheat. They have various applications such as the exchange of digital items, or the exchange of digital coins and digital services between a buyer/client and seller/server. In this work, we formally define and propose a generic blockchain-based construction called "Recurring Contingent Service Payment" (RC-S-P). It (i) lets a fair exchange of digital coins and verifiable service reoccur securely between clients and a server while ensuring that the server is paid if and only if it delivers a valid service, and (ii) ensures the parties' privacy is preserved. RC-S-P supports arbitrary verifiable services, such as "Proofs of Retrievability" (PoR) or verifiable computation and imposes low on-chain overheads. Our formal treatment and construction, for the first time, consider the setting where either client or server is malicious. We also present a concrete efficient instantiation of RC- S-P when the verifiable service is PoR. We implemented the concrete instantiation and analysed its cost. When it deals with a 4-GB outsourced file, a verifier can check a proof in only 90 milliseconds, and a dispute between a prover and verifier is resolved in 0.1 milliseconds. At CCS 2017, two blockchain-based protocols were proposed to support the fair exchange of digital coins and a certain verifiable service; namely, PoR. In this work, we show that these protocols (i) are susceptible to a free-riding attack which enables a client to receive the service without paying the server, and (ii) are not suitable for cases where parties' privacy matters, e.g., when the server's proof status or buyer's file size must remain private from the public. RC- S-P simultaneously mitigates the above attack and preserves the parties' privacy

The sources and characteristics of electronic evidence and artificial intelligence

In this updated edition of the well-established practitioner text, Stephen Mason and Daniel Seng have brought together a team of experts in the field to provide an exhaustive treatment of electronic evidence and electronic signatures. This fifth edition continues to follow the tradition in English evidence text books by basing the text on the law of England and Wales, with appropriate citations of relevant case law and legislation from other jurisdictions

CoStricTor: Collaborative HTTP Strict Transport Security in Tor Browser

HTTP Strict Transport Security (HSTS) is a widely-deployed security feature in modern web browsing. It is also, however, a potential vector for user tracking and surveillance. Tor Browser, a web browser primarily concerned with online anonymity, disables HSTS as a result of this tracking potential. We present the CoStricTor protocol which crowdsources HSTS data among Tor Browser clients. It gives Tor Browser users increased resistance to man-in-the-middle attacks without exposing them to HSTS tracking. Our protocol adapts other privacy-preserving data aggregation algorithms to share data effectively among users with strong local differential privacy guarantees. The CoStricTor protocol resists denial of service attacks by design through our innovative use of Bloom filters to represent complementary data. Our simulations show our protocol can model up to 150,000 websites, providing 10,000 upgrades to HSTS for users

Bridging Information Security and Environmental Criminology Research to Better Mitigate Cybercrime

Cybercrime is a complex phenomenon that spans both technical and human aspects. As such, two disjoint areas have been studying the problem from separate angles: the information security community and the environmental criminology one. Despite the large body of work produced by these communities in the past years, the two research efforts have largely remained disjoint, with researchers on one side not benefitting from the advancements proposed by the other. In this paper, we argue that it would be beneficial for the information security community to look at the theories and systematic frameworks developed in environmental criminology to develop better mitigations against cybercrime. To this end, we provide an overview of the research from environmental criminology and how it has been applied to cybercrime. We then survey some of the research proposed in the information security domain, drawing explicit parallels between the proposed mitigations and environmental criminology theories, and presenting some examples of new mitigations against cybercrime. Finally, we discuss the concept of cyberplaces and propose a framework in order to define them. We discuss this as a potential research direction, taking into account both fields of research, in the hope of broadening interdisciplinary efforts in cybercrime researc

Payment with Dispute Resolution: A Protocol For Reimbursing Frauds\u27 Victims

An Authorised Push Payment (APP) fraud refers to the case where fraudsters deceive a victim to make payments to bank accounts controlled by them. The total amount of money stolen via APP frauds is swiftly growing. Although regulators have provided guidelines to improve victims\u27 protection, the guidelines are vague and the victims are not receiving sufficient protection. To facilitate victims\u27 reimbursement, in this work, we propose a protocol called Payment with Dispute Resolution (PwDR) and formally define it. The protocol lets an honest victim prove its innocence to a third-party dispute resolver while preserving the protocol participants\u27 privacy. It makes black-box use of a standard online banking system. We evaluate its asymptotic cost and runtime via a prototype implementation. Our evaluation indicates that the protocol is efficient. It imposes only O(1) overheads to the customer and bank. Also, it takes a dispute resolver 0.09 milliseconds to settle a dispute between the two parties