Next Seminar on 02.08.2023

Written on 31.07.2023 13:41 by Niklas Medinger

Dear All,

The next seminar(s) take place on 02.08.2023 at 14:00 (Session A) and 14:00 (Session B).

Session A: (14:00-15:30)
Zubayr Khalid, Marvin Schank, Kristian Metzler

Meeting-ID: 967 8620 5841
Kenncode: BT!u5=


Session B: (14:00-14:30)

Moritz Wilhelm


Session A:

14:00 - 14:30

Speaker: Zubayr Khalid

Types of Talk: Master Intro

Advisor: Dr. Julian Loss

Title: GRandLine: First Adaptively Secure One-Round Randomness Beacon with Quadratic Communication Complexity

Research Area: RA1

Abstract: A source of continuous and publicly verifiable randomness is essential for many applications such as cryptocurrencies and financial audits. Existing works on distributed randomness beacons suffer from at least one of the following drawbacks: (i) lack of reconfiguration-friendliness, (ii) security only against a static adversary, (iii) cubic or higher communication cost, or (iv) computationally expensive tools such as Proof-of-Work. We introduce GRandLine, an adaptively secure randomness beacon protocol that overcomes these challenges while providing optimal resilience in the synchronous network setting. Our beacon has dominance over the existing work and to back up our claim we implement our protocol with worldwide geographically distributed AWS EC2 instances and evaluate it against the state-of-the-art randomness beacons OptRand, BRandPiper and DRand in the same setting. In order to achieve the efficiency of GRandLine, we follow an approach of modeling the network as a binary tree data structure where each leaf of the tree represents a party. At each phase of our protocol two sibling nodes merge and agree on a common transcript which encrypts a secret. Eventually the whole network agrees on a common transcript which encrypts a random secret. Besides having geographically distributed virtual machines, we have also included a development environment where one can test the network locally. For the first time, our implementation includes the existence of active adversarial nodes who will try to sabotage the protocol in different stages of execution. Finally, we have discussed ways to optimize the implementation.


14:30 - 15:00

Speaker: Marvin Schank
Type of talk: Master Intro
Advisor: Prof. Dr. Cas Cremers
Title: Formal Analysis of Matrix's End-to-End Encryption
Research Area: RA2: Reliable Security Guarantees
Abstract: Matrix is a federated communication architecture that allows messenger applications like Element to provide end-to-end-encrypted communication to its users. Researchers recently discovered practically exploitable vulnerabilities in Matrix, questioning its security. To tackle the uncertainty of whether Matrix is secure, one must look closely at Matrix's End-To-End-Encryption protocol. With a formal analysis of the protocol, I want to show that Matrix can provide a frame for secure message transmission. In this thesis, I investigate Matrix's underlying encryption techniques, especially Short-Authentication-String, Olm, and Megolm as the main cryptographic subroutines. I convert those concepts into a symbolic model. Based on that model, Tamarin, a state-of-the-art model checker and security verification tool, proves the Matrix-claimed security guarantees.


15:00 - 15:30

Speaker: Kristian Metzler

Type of talk: Bachelor Final

Advisor: Lucjan Hanzlik

Title: Practicality of the Sweep-UC Protocol for Private Coin Swapping

Research Area: RA1

Abstract: Swapping coins (also called atomic swaps) between cryptocurrencies is an important
tool when commercing in the digital sphere. This is due to the many use cases a cryp-tocurrency may or may not fulfill. Having the ability to swap between coins of different
cryptocurrencies allows the user to benefit from both ecosystems, i.e. any shops, pro-grams or websites using the cryptocurrencies, at the same time without having to fully
commit to one specific cryptocurrency. One problems while swapping coins may arise
though: that is the lacking privacy in most atomic swap solutions. As a response the
concept of privacy-preserving atomic swaps emerged which allow exactly what the name
suggests. TumbleBit and A2L are two prominant examples of protocols which allow
an user to privately swap coins of the same type or between different cryptocurrencies.
A recent advancement in this topic is the Sweep-UC protocol, which describes itself
as “the first fair exchange protocol that simultaneously is efficient, minimizes scripting,
and is compatible with a wide range of currencies”.


Session B:

14:00 - 14:30

Speaker: Moritz Wilhelm
Type of talk: Master Intro
Advisor: Ben Stock
Title: A Song of Trust and Archives: Assessing the Dependability of Web Archives for Reproducible Web Security Measurements
Research Area: RA5: Empirical and Behavioural Security

In recent years, artifact evaluation has gained significant importance within the research community, addressing the challenge of achieving replicability in experimental results. Yet, the ephemeral nature of the Web poses a challenge for reproducing Web measurements reliably, as conducting the same data collection at different points in time can lead to inconsistent outcomes. However, Web archives could offer a potential solution to achieve replicability in Web measurements since archival data is intended to remain indefinitely available.

Web archives provide valuable insights into the historical evolution of the Internet by preserving periodically crawled copies of Web pages. Among these archives, the Internet Archive stands out as a prominent repository, containing an extensive collection of 735 billion Web pages spanning from 1996 to the present. Over the years, researchers have repeatedly relied on the Internet Archive to retrospectively conduct historical Web measurements.

In this thesis, we conduct a comprehensive evaluation of the reliability of data obtained from the Internet Archive. The evaluation includes a longitudinal analysis from 2016 to the present, covering a period of 7.5 years. We crawl the top 20,000 domains from the Tranco list and examine their coverage by the archive. Additionally, to minimize potential biases related to popular domains, we repeat the experiment using a randomly sampled subset of 20,000 domains from the complete Tranco one-million list. In addition to the quantitative analysis, we explore qualitative aspects of the data. Specifically, we assess the prevalence of syntactic and semantic differences in security headers among Internet Archive snapshots that are in close temporal proximity. Moreover, we explore the feasibility of leveraging the Internet Archive to simulate live Web security measurements, thereby addressing the challenge of replicability in such studies.

The results of this thesis are expected to provide valuable insights on the dependability of Web archives for Web security measurements, while offering practical guidelines for conducting archive-based studies.

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