Seminar

Talk 1 - by Piyush Kumar: On the Anonymity of Peer-to-Peer Network Anonymity Schemes Used by Cryptocurrencies

Cryptocurrency systems can be subject to deanonymization attacks by exploiting the network-level communication on their peer-to-peer network. Adversaries who control a set of colluding node(s) within the peer-to-peer network can observe transactions being exchanged and infer the parties involved. Thus, various network anonymity schemes have been proposed to mitigate this problem, with some solutions providing theoretical anonymity guarantees.

In this talk, I will discuss about modeling such peer-to-peer network anonymity solutions and evaluate their anonymity guarantees. To do so, we propose a novel framework that uses Bayesian inference to obtain the probability distributions linking transactions to their possible originators. We characterize transaction anonymity with those distributions, using entropy as metric of adversarial uncertainty on the originator's identity. In particular, we model Dandelion, Dandelion++, and Lightning Network. We study different configurations and demonstrate that none of them offers acceptable anonymity to their users. For instance, our analysis reveals that in the widely deployed Lightning
Network, with 1% strategically chosen colluding nodes the adversary can uniquely determine the originator for ≈50% of the total transactions in the network. In Dandelion, an adversary that controls 15% of the nodes has on average uncertainty among only 88 possible originators. Moreover, we observe that due to the way Dandelion and Dandelion++ are designed, increasing the network size does not correspond to an increase in the anonymity set of potential originators.
Alarmingly, our longitudinal analysis of Lightning Network reveals rather an inverse trend---with the growth of the network the overall anonymity decreases.

Bio Piyush:
Piyush is a postdoctoral researcher at KU Leuven in the COSIC research group. He broadly works in the area of network security with a focus on building PET and anti-censorship solutions. Before joining KU Leuven he completed his PhD from IIIT Delhi in 2021. His research is published in reputed venues like IMC, AsiaCCS, PETS, and NDSS.

Talk 2 - by Devashish Gosain: Behind the Curtain: On the Evolution of Internet Filtering in India

Internet censorship is an active area of research where researchers study how different countries engage in large-scale network filtering. To this end, we present a comprehensive measurement study highlighting the evolving Internet filtering within India. We first study the recent mobile app blocking in India and describe in detail the mechanics involved. We analyzed 220 Chinese apps that were blocked due to official government orders. Our research reveals a novel "three-tiered" app censorship scheme, with each tier increasing the sophistication of censorship. After thoroughly analyzing the app censorship mechanisms, we present effective circumvention techniques to bypass the tiered app blocking. We were able to access all the blocked apps with the said techniques. Overall our study highlights the evolving blocking ecosystem in India, and our findings have broader relevance for studying established and emerging censors.
 
Bio Devashish:
Devashish Gosain works in the area of network privacy and censorship. Presently he is a postdoc at the COSIC research group at KU Leuven. Before that, he worked as a postdoc in the INET research group at Max Planck Institute for Informatics for nearly two years. He did his Ph.D. at Indraprastha Institute of Information Technology (IIIT) in Delhi, India. His research has been published at reputed venues like CCS, NDSS, Usenix Security, PETS, INFOCOM, IMC, etc.