The use of TLS in Censorship Circumvention

Фролов, С. В.; Wustrow, Eric

doi:10.14722/ndss.2019.23511

Cited by 58 publications

(44 citation statements)

References 21 publications

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“…the application layer-other forms operate at the network and protocol layers. These forms only identify classes of devices or clients, but are not immune to spoofing [50], [24]. TCP fingerprinting relies on the IPv4, IPv6 and TCP headers to identify the OS and software sending a request [4].…”

Section: Other Forms Of Fingerprintingmentioning

confidence: 99%

FP-Crawlers: Studying the Resilience of Browser Fingerprinting to Block Crawlers

Vastel¹,

Rudametkin²,

Rouvoy³

et al. 2020

Proceedings 2020 Workshop on Measurements, Attacks, and Defenses for the Web

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Data available on the Web, such as financial data or public reviews, provides a competitive advantage to companies able to exploit them. Web crawlers, a category of bot, aim at automating the collection of publicly available Web data. While some crawlers collect data with the agreement of the websites being crawled, most crawlers do not respect the terms of service. CAPTCHAs and approaches based on analyzing series of HTTP requests classify users as humans or bots. However, these approaches require either user interaction or a significant volume of data before they can classify the traffic.In this paper, we study browser fingerprinting as a crawler detection mechanism. We crawled the Alexa top 10K and identified 291 websites that block crawlers. We show that fingerprinting is used by 93 (31.96%) of them and we report on the crawler detection techniques implemented by the major fingerprinters. Finally, we evaluate the resilience of fingerprinting against crawlers trying to conceal themselves. We show that although fingerprinting is good at detecting crawlers, it can be bypassed with little effort by an adversary with knowledge on the fingerprints collected.

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Section: Other Forms Of Fingerprintingmentioning

confidence: 99%

FP-Crawlers: Studying the Resilience of Browser Fingerprinting to Block Crawlers

Vastel¹,

Rudametkin²,

Rouvoy³

et al. 2020

Proceedings 2020 Workshop on Measurements, Attacks, and Defenses for the Web

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“…The unencrypted Server Name Indication (SNI) enables an eavesdropper to determine which specific web site a client is connected to among the sites hosted by the same server. The eavesdropper can also fingerprint the client [46] or distinguish censorship-circumvention tools that try to mimic TLS traffic [23,29]. TLS 1.3 [45] takes a few protective measures: e.g., less unencrypted metadata during the handshake, and an experimental extension for encrypted SNI [45,47].…”

Section: Motivation and Applicationsmentioning

confidence: 99%

“…Moreover, it has been argued that most traffic-morphing tools do not achieve unobservability in real-world settings due to discrepancies between their implementations and the systems that they try to imitate, because of the uncovered behavior of side protocols, error handling, responses to probing, etc. [23,29,54]. We believe that for a wide class of applications, using pseudo-random uniform blobs, either alone or in combination with other lower-level tools, is a potential solution in a different direction.…”

Section: Related Workmentioning

confidence: 99%

Reducing Metadata Leakage from Encrypted Files and Communication with PURBs

Nikitin

Barman

Lueks

et al. 2019

Proceedings on Privacy Enhancing Technologies

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Most encrypted data formats, such as PGP, leak substantial metadata from their plaintext headers, such as the format version, the encryption schemes used, number of recipients who can decrypt the data, and even the identities of these recipients. This leakage can pose security and privacy risks to users, e.g., by revealing the full membership of a group of collaborators from a single encrypted e-mail, or by enabling an eavesdropper to fingerprint the precise encryptionsoftware version and configuration the sender used. We propose to improve security and privacy hygiene by designing future encrypted data formats such that anyone without a relevant decryption key cannot learn anything at all from a ciphertext, apart from its length, and as little as possible even from that. We present Padded Uniform Random Blobs or PURBs, an encrypted format that strongly minimizes a ciphertext's leakage via metadata or length. Without a decryption key, a PURB is indistinguishable from a uniform random bit string. Legitimate recipients can efficiently decrypt the PURB, even when it is encrypted for any number of recipients' public keys and/or passwords, and when these public keys are from different cryptographic schemes. PURBs use a novel padding scheme to reduce potential information-leakage via the ciphertext's length L to the asymptotic minimum of O(log log L) bits, comparable to padding to a power of two, but with a much lower padding overhead of at most 12%, which decreases with larger payloads.*Both are corresponding authors and share first authorship. Motivation and BackgroundWe begin this section by giving examples of where PURBs can be useful, and describe the Integrated Encryption Scheme that we later use as a starting point in our design. Motivation and ApplicationsPURBs is a paradigm for designing encryption data formats; it efficiently protects sensitive metadata. Our goal is to define a general approach applicable to most of the common data-encryption scenarios such

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“…To evade censors, we must send a plausible SNI value (sending no SNI is uncommon and easily blocked-only 1% of TLS connections do not send the SNI extension [21]), and we must have the server respond with a plausible (and corresponding) certificate. Even if we manage to avoid sending either in the clear (e.g.…”

Section: Tlsmentioning

confidence: 99%

“…The application attempts to decrypt the first application data record from the client using a key derived from the secret seed, client, and server randoms. We use the uTLS library [21,41] on both the application and client to allow us to change the TLS secrets being used after the handshake.…”

Section: Maskmentioning

confidence: 99%

Conjure

Фролов

Wampler

Tan

et al. 2019

Proceedings of the 2019 ACM SIGSAC Conference on Computer and Communications Security

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Refraction Networking (formerly known as "Decoy Routing") has emerged as a promising next-generation approach for circumventing Internet censorship. Rather than trying to hide individual circumvention proxy servers from censors, proxy functionality is implemented in the core of the network, at cooperating ISPs in friendly countries. Any connection that traverses these ISPs could be a conduit for the free flow of information, so censors cannot easily block access without also blocking many legitimate sites. While one Refraction scheme, TapDance, has recently been deployed at ISP-scale, it suffers from several problems: a limited number of "decoy" sites in realistic deployments, high technical complexity, and undesirable tradeoffs between performance and observability by the censor. These challenges may impede broader deployment and ultimately allow censors to block such techniques. We present Conjure, an improved Refraction Networking approach that overcomes these limitations by leveraging unused address space at deploying ISPs. Instead of using real websites as the decoy destinations for proxy connections, our scheme connects to IP addresses where no web server exists leveraging proxy functionality from the core of the network. These phantom hosts are difficult for a censor to distinguish from real ones, but can be used by clients as proxies. We define the Conjure protocol, analyze its security, and evaluate a prototype using an ISP testbed. Our results suggest that Conjure can be harder to block than TapDance, is simpler to maintain and deploy, and offers substantially better network performance. CCS CONCEPTS • Networks → Network security; • Social and professional topics → Censorship.

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The use of TLS in Censorship Circumvention

Cited by 58 publications

References 21 publications

FP-Crawlers: Studying the Resilience of Browser Fingerprinting to Block Crawlers

FP-Crawlers: Studying the Resilience of Browser Fingerprinting to Block Crawlers

Reducing Metadata Leakage from Encrypted Files and Communication with PURBs

Conjure

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