Helmholtz Center for Information Security
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FeIDo: Recoverable FIDO2 Tokens Using Electronic IDs (Extended Version)
Get PDFTwo-factor authentication (2FA) mitigates the security risks of passwords as sole authentication factor. FIDO2---the de facto standard for interoperable web authentication---leverages strong, hardware-backed second factors. However, practical challenges hinder wider FIDO2 user adoption for 2FA tokens, such as the extra costs (30 per token) or the risk of inaccessible accounts upon token loss/theft.
To tackle the above challenges, we propose FeIDo, a virtual FIDO2 token that combines the security and interoperability of FIDO2 2FA authentication with the prevalence of existing eIDs (e.g., electronic passports). Our core idea is to derive FIDO2 credentials based on personally-identifying and verifiable attributes---name, date of birth, and place of birth---that we obtain from the user's eID. As these attributes do not change even for refreshed eID documents, the credentials "survive" token loss. Even though FeIDo operates on privacy-critical data, all personal data and resulting FIDO2 credentials stay unlinkable, are never leaked to third parties, and are securely managed in attestable hardware containers (e.g., SGX enclaves). In contrast to existing FIDO2 tokens, FeIDo can also derive and share verifiable meta attributes (anonymous credentials) with web services. These enable verified but pseudonymous user checks, e.g., for age verification (e.g., "is adult")
Anomaly-based Filtering of Application-Layer DDoS Against DNS Authoritatives
Get PDFAuthoritative DNS infrastructures are at the core of the Internet ecosystem.
But how resilient are typical authoritative DNS name servers against application-layer Denial-of-Service attacks?
In this paper, with the help of a large country-code TLD operator, we assess the expected attack load and DoS countermeasures.
We find that standard botnets or even single-homed attackers can overload the computational resources of authoritative name servers—even if redundancy such as anycast is in place.
To prevent the resulting devastating DNS outages, we assess how effective upstream filters can be as a last resort.
We propose an anomaly detection defense that allows both, well-behaving high-volume DNS resolvers as well as low-volume clients to continue name lookups—while blocking most of the attack traffic.
Upstream ISPs or IXPs can deploy our scheme and drop attack traffic to reasonable query loads at or below 100k queries per second at a false positive rate of 1.2 % to 5.7 % (median 2.4 %)
SEAL: Capability-Based Access Control for Data-Analytic Scenarios
Get PDFData science is the basis for various disciplines in the Big-Data era. Due to the high volume, velocity, and variety of big data, data owners often store their data in data servers. Past few years, many computation techniques have emerged to protect the security and privacy of such shared data while enabling analysis thereon. Hence, access-control systems must provide a fine-grained, multi-layer mechanism to protect data. However, the existing systems and frameworks fail to satisfy all these requirements and resolve the trust issue between data owners and analysts.
In this paper, we propose SEAL as a framework to protect the security and privacy of shared data. SEAL enables computations on shared data while they remain under the complete control of data owners through pre-defined policies. Our framework employs the capability-object model to define flexible access policies. SEAL's access-control system supports delegating and revoking access privileges and other access-control customizations. In addition, SEAL can assign security labels to privacy-sensitive data and track them to enable data owners to define where and when a data analyst can access their data. We demonstrate the practicability of our approach by presenting a prototype implementation of SEAL.
Furthermore, we display the flexibility of our framework by implementing multiple data-analytic scenarios, which cover different applications
You Call This Archaeology? Evaluating Web Archives for Reproducible Web Security Measurements
Get PDFGiven the dynamic nature of the Web, security measurements on it suffer from reproducibility issues. In this paper we take a systematic look into the potential of using web archives for web security measurements. We first evaluate an extensive set of web archives as potential sources of archival data, showing the superiority of the Internet Archive with respect to its competitors. We then assess the appropriateness of the Internet Archive for historical web security measurements, detecting subtleties and possible pitfalls in its adoption. Finally, we investigate the feasibility of using the Internet Archive to simulate live security measurements, using recent archival data in place of live data. Our analysis shows that archive-based security measurements are a promising alternative to traditional live security measurements, yet reproducible by design. As an important contribution, we identify insights and best practices for future archive-based security measurements
Logics and Algorithms for Hyperproperties
Get PDFSystem requirements related to concepts like information flow, knowledge, and robustness cannot be judged in terms of individual system executions, but rather require an analysis of the relationship between multiple executions. Such requirements belong to the class of hyperproperties, which generalize classic trace properties to properties of sets of traces. During the past decade, a range of new specification logics has been introduced with the goal of providing a unified theory for reasoning about hyperproperties. This paper gives an overview on the current landscape of logics for the specification of hyperproperties and on algorithms for satisfiability checking, model checking, monitoring, and synthesis
Revisiting the Indifferentiability of the Sum of Permutations
Get PDFThe sum of two n-bit pseudorandom permutations is known to behave like a pseudorandom function with n bits of security. A recent line of research has investigated the security of two public n-bit permutations and its degree of indifferentiability. Mandal et al. (INDOCRYPT 2010) proved 2n/3-bit security, Mennink and Preneel (ACNS 2015) pointed out a non-trivial flaw in their analysis and re-proved (2n/3-\log_2(n))-bit security. Bhattacharya and Nandi (EUROCRYPT 2018) eventually improved the result to n-bit security. Recently, Gunsing at CRYPTO 2022 already observed that a proof technique used in this line of research only holds for sequential indifferentiability. We revisit the line of research in detail, and observe that the strongest bound of n-bit security has two other serious issues in the reasoning, the first one is actually the same non-trivial flaw that was present in the work of Mandal et al., while the second one discards biases in the randomness influenced by the distinguisher. More concretely, we introduce two attacks that show limited potential of different approaches. We (i) show that the latter issue that discards biases only holds up to 2^{3n/4} queries, and (ii) perform a differentiability attack against their simulator in 2^{5n/6} queries. On the upside, we revive the result of Mennink and Preneel and show (2n/3-\log_2(n))-bit regular indifferentiability security of the sum of public permutations
Lattice-based Authenticated Key Exchange with Tight Security
Get PDFWe construct the first tightly secure authenticated key exchange (AKE) protocol from lattices. Known tight constructions are all based on Diffie-Hellman-like assumptions. Thus, our protocol is the first construction with tight security from a post-quantum assumption.
Our AKE protocol is constructed tightly from a new security notion for key encapsulation mechanisms (KEMs), called one-way security against checkable chosen-ciphertext attacks (OW- ChCCA). We show how an OW-ChCCA secure KEM can be tightly constructed based on the Learning With Errors assumption, leading to the desired AKE protocol. To show the usefulness of OW-ChCCA security beyond AKE, we use it to construct the first tightly bilateral selective-opening
(BiSO) secure PKE. BiSO security is a stronger selective-opening notion proposed by Lai et al. (ASIACRYPT 2021)
To Cloud or not to Cloud: A Qualitative Study on Self-Hosters’ Motivation, Operation, and Security Mindset
Get PDFDespite readily available cloud services, some people decide to self-host internal or external services for themselves or their organization. In doing so, a broad spectrum of commercial, institutional, and private self-hosters take responsibility for their data, security, and reliability of their operations.
Currently, little is known about what motivates these self- hosters, how they operate and secure their services, and which challenges they face. To improve the understanding of self-hosters’ security mindsets and practices, we conducted a largescale survey (NS=994) with users of a popular self-hosting suite and in-depth follow-up interviews with selected commercial, non-profit, and private users (NI =41).
We found exemplary behavior in all user groups; however, we also found a significant part of self-hosters who approach security in an unstructured way, regardless of social or organizational embeddedness. Vague catch-all concepts such as firewalls and backups dominate the landscape, without proper reflection on the threats they help mitigate. At times, self-hosters engage in creative tactics to compensate for a potential lack of expertise or experience
A Rowhammer Reproduction Study Using the Blacksmith Fuzzer
Get PDFRowhammer is a hardware vulnerability that can be exploited to induce bit flips in dynamic random access memory (DRAM), compromising the security of a computer system. Multiple ways of exploiting Rowhammer have been shown and even in the presence of mitigations such as target row refresh (TRR), DRAM modules remain partially vulnerable.
In this paper, we present a large-scale reproduction study on the Rowhammer vulnerability using the Blacksmith Rowhammer fuzzer. The main focus of our study is the impact of the fuzzing environment. Our study, uses a diverse set of 10 DRAM chips from various manufacturers, with different capacities and memory frequencies. We show that the runtime, used seeds, and DRAM coverage of the fuzzer have been underestimated in previous work. Additionally, we study the entire hardware setup's impact on the transferability of Rowhammer by fuzzing the same DRAM on 4 identical machines. The transferability study heavily relates to Rowhammer-based physically unclonable functions (PUFs) which rely on the stability of Rowhammer-induced bit flips. Our results confirm the findings of the Blacksmith fuzzer, showing that even modern DRAM chips are vulnerable to Rowhammer. In addition, we show that PUFs are challenging to achieve on commodity systems due to the high variability of Rowhammer bit flips
It's (DOM) Clobbering Time: Attack Techniques, Prevalence, and Defenses
Get PDFDOM Clobbering is a type of code-less injection attack where attackers insert a piece of non-script, seemingly benign HTML markup into a webpage and transform it to executable code by exploiting the unforeseen interactions between JavaScript code and the runtime environment. The attack techniques, browser behaviours, and vulnerable code patterns that enable DOM Clobbering has not been studied yet, and in this paper, we undertake one of the first evaluations of the state of DOM Clobbering on the Web platform. Starting with a comprehensive survey of existing literature and dynamic analysis of 19 different mobile and desktop browsers, we systematize DOM Clobbering attacks, uncovering 31.4K distinct markups that use five different techniques to unexpectedly overwrite JavaScript variables in at least one browser. Then, we use our systematization to identify and characterize program instructions that can be overwritten by DOM Clobbering, and use it to present TheThing, an automated system that detects clobberable data flows to security-sensitive instructions. We instantiate TheThing on the top of the Tranco top 5K sites, quantifying the prevalence and impact of DOM Clobbering in the wild. Our evaluation uncovers that DOM Clobbering vulnerabilities are ubiquitous, with a total of 9,467 vulnerable data flows across 491 affected sites, making it possible to mount arbitrary code execution, open redirections, or client-side request forgery attacks also against popular websites such as Fandom, Trello, Vimeo, TripAdvisor, WikiBooks and GitHub, that were not exploitable through the traditional attack vectors. Finally, in this paper, we also evaluate the robustness of the existing countermeasures, such as HTML sanitizers and Content Security Policy, against DOM Clobbering