Ahmed Khurshid

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Networks are complex and prone to bugs. Existing tools that check configuration files and data-plane state operate offline at timescales of seconds to hours, and cannot detect or prevent bugs as they arise. Is it possible to <i>check network-wide invariants in real time</i>, as the network state evolves? The key challenge here is to achieve extremely low(More)
Diagnosing problems in networks is a time-consuming and error-prone process. Existing tools to assist operators primarily focus on analyzing control plane configuration. Configuration analysis is limited in that it cannot find bugs in router software, and is harder to generalize across protocols since it must model complex configuration languages and(More)
Anonymity systems such as Tor aim to enable users to communicate in a manner that is untraceable by adversaries that control a small number of machines. To provide efficient service to users, these anonymity systems make full use of forwarding capacity when sending traffic between intermediate relays. In this paper, we show that doing this leaks information(More)
The ability to forward packets on the Internet is highly intertwined with the availability and robustness of the Domain Name System (DNS) infrastructure. Unfortunately, the DNS suffers from a wide variety of problems arising from implementation errors, including vulnerabilities, bogus queries, and proneness to attack. In this work, we present a preliminary(More)
Functional switches are often regulated by dynamic protein modifications. Assessing protein functions, in vivo, and their functional switches remains still a great challenge in this age of development. An alternative methodology based on in silico procedures may facilitate assessing the multifunctionality of proteins and, in addition, allow predicting(More)
Post-translational modification (PTM) of a protein is an important event in regulating cellular functions. An algorithm, MAPRes, has been developed for mining associations among PTM sites and the preferred amino acids in their vicinity. The algorithm has been implemented to O-glycosylation and O-phosphorylation data (phosphorylated/glycosylated(More)
Disruption-tolerant network (DTN) is an intermittently connected network where the traditional end-to-end data communication between a source-destination pair is hardly possible. Instead, nodes opportunistically replicate the same packet several times and try to deliver them through multiple paths. Due to this multi-copy forwarding scheme, denial of service(More)
In this paper, we propose countermeasures to mitigate damage caused by spoofing attacks in Delay-Tolerant Networks (DTNs). In our model, an attacker spoofs someone else's address (the victim's) to absorb packets from the network intended for that victim. Address spoofing is arguably a very severe attack in DTNs, compared to other known attacks, such as(More)
Cloud computing has the potential to bring sophisticated computing facility at the doorsteps of users. The performance of services hosted at a cloud generally depends on its computation, storage and networking models. Since the storage and communication costs in a data-intensive application usually dominate the overall cost, we analyze the performance of(More)
Understanding and troubleshooting wide area networks (such as military backbone networks and ISP networks) are challenging tasks due to their large, distributed, and highly dynamic nature. Building a system that can record and replay fine-grained behaviors of such networks would simplify this problem by allowing operators to recreate the sequence and(More)