Trinabh Gupta

Evolution of an online social aggregation network: an empirical study

Many factors such as the tendency of individuals to develop relationships based on mutual acquaintances, proximity, common interests, or combinations thereof, are known to contribute toward evolution of social networks. In this paper, we analyze an evolving online social aggregator FriendFeed, which collates content generated by participating individuals on a variety of Web 2.0 services and allows easy dissemination of the aggregated content to other participants of the aggregator. Analyzing data collected between September 2008 and May 2009, we find that although preferential attachment captures the evolution of the network, its influence varies significantly based on how long ago a user joined the service. In particular, preferential attachment does not appear to apply to new entrants of the FriendFeed service. Analysis suggests that proximity bias plays an important role in link formation. We study the influence of common foci and find that individuals have a greater affinity toward those with similar interests.

TARDiS: A Branch-and-Merge Approach To Weak Consistency

This paper presents the design, implementation, and evaluation of TARDiS (Transactional Asynchronously Replicated Divergent Store), a transactional key-value store explicitly designed for weakly-consistent systems. Reasoning about these systems is hard, as neither causal consistency nor per-object eventual convergence allow applications to deal satisfactorily with write-write conflicts. TARDiS instead exposes as its fundamental abstraction the set of conflicting branches that arise in weakly-consistent systems. To this end, TARDiS introduces a new concurrency control mechanism: branch-on-conflict. On the one hand, TARDiS guarantees that storage will appear sequential to any thread of execution that extends a branch, keeping application logic simple. On the other, TARDiS provides applications, when needed, with the tools and context necessary to merge branches atomically, when and how applications want. Since branch-on-conflict in TARDiS is fast, weakly-consistent applications can benefit from adopting this paradigm not only for operations issued by different sites, but also, when appropriate, for conflicting local operations. We find that TARDiS reduces coding complexity for these applications and that judicious branch-on-conflict can improve their local throughput at each site by two to eight times.

Taming uncertainty in distributed systems with help from the network

Network and process failures cause complexity in distributed applications. When a remote process does not respond, the application cannot tell if the process or network have failed, or if they are just slow. Without this information, applications can lose availability or correctness. To address this problem, we propose Albatross, a service that quickly reports to applications the current status of a remote process---whether it is working and reachable, or not. Albatross is targeted at data centers equipped with software defined networks (SDNs), allowing it to discover and enforce network partitions: Albatross borrows the old observation that it can be better to cause a problem than to live with uncertainty, and applies this idea to networks. When enforcing partitions, Albatross avoids disruption by disconnecting only individual processes (not entire hosts), and by allowing them to reconnect if the application chooses. We show that, under Albatross, distributed applications can bypass the complexity caused by network failures and that they become more available.

Pretzel: Email encryption and provider-supplied functions are compatible

Emails today are often encrypted, but only between mail servers---the vast majority of emails are exposed in plaintext to the mail servers that handle them. While better than no encryption, this arrangement leaves open the possibility of attacks, privacy violations, and other disclosures. Publicly, email providers have stated that default end-to-end encryption would conflict with essential functions (spam filtering, etc.), because the latter requires analyzing email text. The goal of this paper is to demonstrate that there is no conflict. We do so by designing, implementing, and evaluating Pretzel. Starting from a cryptographic protocol that enables two parties to jointly perform a classification task without revealing their inputs to each other, Pretzel refines and adapts this protocol to the email context. Our experimental evaluation of a prototype demonstrates that email can be encrypted end-to-end and providers can compute over it, at tolerable cost: clients must devote some storage and processing, and provider overhead is roughly 5x versus the status quo.

Toward practical and private online services

The designs of today’s common online services (social networks, media streaming, messaging, email, etc.) are in conflict with privacy. Indeed, there have been many incidents (hacks, accidental disclosures, etc.) where private information has leaked. My research aims to build systems that provide strong privacy guarantees and are practical (that is, have functionality and costs comparable to that of the status quo). In the talk, I will describe the challenges in building such systems and and how I address them. As an example, Popcorn is a Netflix-like media delivery system that provably hides (even from the content distributor) which movie a user is watching, is otherwise consistent with the prevailing commercial regime (copyrights, etc.), and achieves plausibly deployable performance (the per-request dollar cost is 3.87 times that of a non-private system). Bio Trinabh Gupta is a PhD candidate at The University of Texas at Austin. He is also a visiting academic in NYU’s systems group. His research interests are in systems, security, and privacy, and he has worked on privacy-preserving online services, and failure detection in distributed systems. His advisors are Lorenzo Alvisi and Michael Walfish. Prior to being a PhD student he was a computer science undergraduate at Indian Institute of Technology Delhi (IITD). Faculty Host: David Cash