UWSpace

UWSpace is the University of Waterloo’s institutional repository for the free, secure, and long-term home of research produced by faculty, students, and staff.

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Recent Submissions

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    Upgrading Security Properties for Updatable Public-Key Encryption through Modular Transformations
    (University of Waterloo, 2026-09-16) Kumar, Pranshu
    Updatable public-key encryption (UPKE) serves as a key tool for ensuring compromise resilience in dynamic group messaging systems such as MLS and TreeKEM. Prior work has introduced a variety of security notions for UPKE, including chosen-randomness and chosen-update security, chosen ciphertext attack (CCA) security, adaptive corruption resilience, public verifiability, and adversarially generated forking update structures. However, these notions make the security definition complex, and there is very little work on instantiating schemes that satisfy it. In this work, we develop generic transformations that enable a sequence of upgrades from weaker to stronger UPKE notions, each introducing additional security properties. These security properties include straightline and forking update structures, selective and adaptive corruptions, public verifiability, chosen randomness and chosen-update security, and CPA and CCA notions. We define intermediate security notions that serve as useful stepping stones while adding the aforementioned properties. Some transformations rely only on standard tools such as random oracles, while others additionally exploit natural structural properties of schemes such as update uniformity and ciphertext updatability, which we identify and formalize in this work. This modular structure allows one to isolate and focus on specific combinations of properties of interest, facilitating easier security analysis.
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    Persistence service for non-persistent P2P systems
    (University of Waterloo, 2012-09-04) Ahmed, Reaz; Shahriar, Nashid; Sharmin, Mahfuza; Boutaba, Raouf; Mathieu, Bertrand
    Ensuring content persistence with minimal replication overhead is a prerequisite for providing any consistent service over a peer-to-peer (P2P) overlay. This paper introduces S-DATA, a bandwidth efficient protocol for achieving highly available P2P systems with minimal replication overhead. When considering a global P2P system, the cyclic behaviour of peers situated at different time zones can be found complementary of one another. In S-DATA, peers with complementary diurnal availability patterns collaborate in small replication groups and host each other's content in turn to ensure 24/7 availability. In this work we present a mathematical model for measuring time-base availability with (β - 1) redundancy as a function of replication group size and peer uptime behaviour. We also simulate the S-Data protocol in the PeerSim simulator and compare its performance against a few other time-based replication protocols.
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    DEWS: A decentralized engine for web search
    (University of Waterloo, 2012-09-04) Ahmed, Reaz; Haque, Rakibul; Bari, Md. Faizul; Boutaba, Raouf; Mathieu, Bertrand
    The way we explore the web is largely governed by centrally controlled, clustered search engines, which is not healthy for our freedom in the Internet. A better solution is to enable the web to index itself in a decentralized manner. In this work we propose a decentralized web search mechanism, named DEWS, which will enable the existing webservers to collaborate with each other to form a distributed index of the web. DEWS can rank the search results based on query keyword relevance and relative importance of websites. DEWS also supports approximate matching of query keywords and incremental retrieval of search results in a decentralized manner. We use the standard LETOR 3.0 dataset to validate the DEWS protocol. Simulation results show that the ranking accuracy of DEWS is very close to the centralized case, while network overhead for collaborative search and indexing is logarithmic on network size. Simulation results also show that DEWS is resilient to changes in the available pool of indexing webservers and works efficiently even in presence of heavy query load.
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    αRoute: A name based routing scheme for information centric networks
    (University of Waterloo, 2012-09-04) Ahmed, Reaz; Bari, Md. Faizul; Chowdhury, Shihabur Rahman; Rabbani, Md. Golam; Boutaba, Raouf; Mathieu, Bertrand
    One of the crucial building blocks for Information Centric Networking (ICN) is a name based routing scheme that can route directly on content names instead of IP addresses. However, moving the address space from IP addresses to content names brings scalability issues to a whole new level, due to two reasons. First, name aggregation is not as trivial a task as the IP address aggregation in BGP routing. Second, the number of addressable contents in the Internet is several orders of magnitude higher than the number of IP addresses. With the current size of the Internet, name based, anycast routing is very challenging specifically when routing efficiency is of prime importance. We propose a novel name-based routing scheme (αRoute) for ICN that offers efficient bandwidth usage, guaranteed content lookup and scalable routing table size. αRoute consists of two components: an alphanumeric Distributed Hash Table (DHT) and an overlay to underlay (Internet topology) mapping algorithm. Simulation results show that αRoute performs significantly better than Content Centric Network (CCN) [1] in terms of network bandwidth usage, lookup latency and load balancing.
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    Minimizing cache usage in paging
    (University of Waterloo, 2012-09-30) L'Opez-Ortiz, Alejandro; Salinger, Alejandro
    Traditional paging models seek algorithms that maximize their performance while using the maximum amount of cache resources available. However, in many applications this resource is shared or its usage involves a cost. In this work we introduce the Minimum Cache Usage problem, which is an extension to the classic paging problem that accounts for the efficient use of cache resources by paging algorithms. In this problem, the cost of a paging algorithm is a combination of both its number of faults and the amount of cache it uses, where the relative cost of faults and cache usage can vary with the application. We present a simple family of online paging algorithms that adapt to the ratio between cache and fault costs, achieving competitive ratios that vary with, and that are between 2 and the cache size k. Furthermore, for sequences with high locality of reference, we show that the competitive ratio is at most 2, and provide evidence of the competitiveness of our algorithms on real world traces. Finally, we show that the offline problem admits a polynomial time algorithm. In doing so, we define a reduction of paging with cache usage to weighted interval scheduling on identical machines.