arXiv subjects

Sambuddho Chakravarty

Publications and source records attributed to Sambuddho Chakravarty.

5 recordsLinked to original sources

arXiv2026

The Invisible Ink of the Android Malware World: A Longitudinal Study on the Usage of Covert Communication Channels

Proxies, VPNs and Tor have long helped the privacy community and users in censored regions to fight censorship. However, the same tools can be maliciously exploited by malware and botnets to conceal their communication to external command and control servers. Despite being a critical concern fueled by the proliferation of malware based attacks, no longitudinal studies have analyzed how malware applications use covert channels (CC) to evade detection. We fill this gap by performing the first study of the usage of covert channels in the Android malware ecosystem. To that end, we develop a multistage pipeline that combines static and dynamic analysis to investigate both system and network-level features. We applied this pipeline on a corpus of 3.5M Android malware spanning 2009 to July 2025. Our carefully crafted static validation rules uncovered 288K APKs that used CCs spanning 511 malware families and CC usage growing exponentially from 0.30\% (2012) to 50\% (2025). Overall, in dynamic analysis, we identified 19,308 unique IP addresses being contacted in 85 countries, out of which we were able to explicitly validate the presence of CCs for 59 IP addresses across 17 countries. Further, we performed a longitudinal dataset study spanning over 16 years for CC based malware and found that CC usage has evolved, \textit{e.g.,} some malware adopted by using more than one CCs; others switched between them periodically (one family switched CC usage 40 times from 2019 to 2025).

cs.CR↗

arXiv2020

The Road Not Taken: Re-thinking the Feasibility of Voice Calling Over Tor

Anonymous VoIP calls over the Internet holds great significance for privacy-conscious users, whistle-blowers and political activists alike. Prior research deems popular anonymization systems like Tor unsuitable for providing requisite performance guarantees that real-time applications like VoIP need. Their claims are backed by studies that may no longer be valid due to constant advancements in Tor. Moreover, we believe that these studies lacked the requisite diversity and comprehensiveness. Thus, conclusions from these studies led them to propose novel and tailored solutions. However, no such system is available for immediate use. Additionally, operating such new systems would incur significant costs for recruiting users and volunteered relays, to provide the necessary anonymity guarantees. It thus becomes imperative that the exact performance of VoIP over Tor be quantified and analyzed so that the potential performance bottlenecks can be amended. We thus conducted an extensive empirical study across various in-lab and real-world scenarios to shed light on VoIP performance over Tor. In over 0.5 million measurements spanning 12 months, across seven countries and covering about 6650 Tor relays, we observed that Tor supports good voice quality (Perceptual Evaluation of Speech Quality (PESQ) >3 and oneway delay <400ms) in more than 85% of cases. Further analysis indicates that in general for most Tor relays, the contentions due to cross-traffic were low enough to support VoIP calls, that are anyways transmitted at low rates (<120 Kbps). Our findings are supported by concordant measurements using iperf that show more than the adequate available bandwidth for most cases. Data published by the Tor Metrics also corroborates the same. Hence, unlike prior efforts, our research reveals that Tor is suitable for supporting anonymous VoIP calls.

cs.CR↗

arXiv2018

Where The Light Gets In: Analyzing Web Censorship Mechanisms in India

This paper presents a detailed study of the Internet censorship in India. We consolidated a list of potentially blocked websites from various public sources to assess censorship mechanisms used by nine major ISPs. To begin with, we demonstrate that existing censorship detection tools like OONI are grossly inaccurate. We thus developed various techniques and heuristics to correctly assess censorship and study the underlying mechanism involved in these ISPs. At every step we corroborated our finding manually to test the efficacy of our approach, a step largely ignored by others. We fortify our findings by adjudging the coverage and consistency of censorship infrastructure, broadly in terms of average number of network paths and requested domains the infrastructure surveils. Our results indicate a clear disparity among the ISPs, on how they install censorship infrastructure. For instance, in Idea network we observed the censorious middleboxes on over 90% of our tested intra-AS paths whereas for Vodafone, it is as low as 2.5%. We conclude our research by devising our own novel anti-censorship strategies, that does not depend on third party tools (like proxies, Tor and VPNs etc.). We managed to anti-censor all blocked websites in all ISPs under test.

cs.CY↗

arXiv2018

Few Throats to Choke: On the Current Structure of the Internet

The original design of the Internet was a resilient, distributed system, that maybe able to route around (and therefore recover from) massive disruption --- up to and including nuclear war. However, network routing effects and business decisions cause traffic to often be routed through a relatively small set of Autonomous Systems (ASes). This is not merely an academic issue; it has practical implications --- some of these frequently appearing ASes are hosted in censorious nations. Other than censoring their own citizens' network access, such ASes may inadvertently filter traffic for other foreign customer ASes. In this paper, we examine the extent of routing centralization in the Internet; identify the major players who control the "Internet backbone"; and point out how many of these are, in fact, under the jurisdiction of censorious countries (specifically, Russia, China, and India). Further, we show that China and India are not only the two largest nations by number of Internet users, but that many users in free and democratic countries are affected by collateral damage caused due to censorship by such countries.

cs.NI↗

arXiv2017

The Devils in The Details: Placing Decoy Routers in the Internet

Decoy Routing, the use of routers (rather than end hosts) as proxies, is a new direction in anti-censorship research. Decoy Routers (DRs), placed in Autonomous Systems, proxy traffic from users; so the adversary, e.g., a censorious government, attempts to avoid them. It is quite difficult to place DRs so the adversary cannot route around them for example, we need the cooperation of 850 ASes to contain China alone. In this paper, we consider a different approach. We begin by noting that DRs need not intercept all the network paths from a country, just those leading to Overt Destinations, i.e., unfiltered websites hosted outside the country (usually popular ones, so that client traffic to the OD does not make the censor suspicious. Our first question is; How many ASes are required for installing DRs to intercept a large fraction of paths from, e.g., China to the top n websites (as per Alexa)? How does this number grow with n? Few ASes (approx. 30) intercept over 90% of paths to the top n sites, for n = 10, 20...200. Our first contribution is to demonstrate with real paths that the number of ASes required for a world-wide DR framework is small (approx. 30). Further, censor nations attempts to filter traffic along the paths transiting these 30 ASes will not only block their own citizens, but others residing in foreign ASes. Our second contribution in this paper is to consider the details of DR placement: not just in which ASes DRs should be placed to intercept traffic, but exactly where in each AS. We find that even with our small number of ASes, we still need a total of about 11,700 DRs.We conclude that, even though a DR system involves far fewer ASes than previously thought, it is still a major undertaking. For example, the current routers cost over 10.3 billion USD, so if DR at line speed requires all new hardware, the cost alone would make such a project unfeasible for most actors.

cs.CR↗