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Projeto de investigação
Secure and Scalable Platform for Massive-scale Mobile Applications
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Autores
Publicações
Cloud-edge hybrid applications
Publication . Linde, Albert van der; Preguiça, Nuno; Leitão, João
Many modern applications are designed to provide interactions among users, including multi-
user games, social networks and collaborative tools. Users expect application response time to
be in the order of milliseconds, to foster interaction and interactivity.
The design of these applications typically adopts a client-server model, where all interac-
tions are mediated by a centralized component. This approach introduces availability and fault-
tolerance issues, which can be mitigated by replicating the server component, and even relying on
geo-replicated solutions in cloud computing infrastructures. Even in this case, the client-server
communication model leads to unnecessary latency penalties for geographically close clients and
high operational costs for the application provider.
This dissertation proposes a cloud-edge hybrid model with secure and ecient propagation
and consistency mechanisms. This model combines client-side replication and client-to-client
propagation for providing low latency and minimizing the dependency on the server infras-
tructure, fostering availability and fault tolerance. To realize this model, this works makes the
following key contributions.
First, the cloud-edge hybrid model is materialized by a system design where clients maintain
replicas of the data and synchronize in a peer-to-peer fashion, and servers are used to assist
clients’ operation. We study how to bring most of the application logic to the client-side, us-
ing the centralized service primarily for durability, access control, discovery, and overcoming
internetwork limitations.
Second, we dene protocols for weakly consistent data replication, including a novel CRDT
model (∆-CRDTs). We provide a study on partial replication, exploring the challenges and
fundamental limitations in providing causal consistency, and the diculty in supporting client-
side replicas due to their ephemeral nature.
Third, we study how client misbehaviour can impact the guarantees of causal consistency.
We propose new secure weak consistency models for insecure settings, and algorithms to enforce
such consistency models.
The experimental evaluation of our contributions have shown their specic benets and
limitations compared with the state-of-the-art. In general, the cloud-edge hybrid model leads to
faster application response times, lower client-to-client latency, higher system scalability as fewer clients need to connect to servers at the same time, the possibility to work oine or disconnected
from the server, and reduced server bandwidth usage.
In summary, we propose a hybrid of cloud-and-edge which provides lower user-to-user la-
tency, availability under server disconnections, and improved server scalability – while being
ecient, reliable, and secure.
Transaction Processing over Geo-Partitioned Data
Publication . Braz, Sofia Frederico de Sousa; Preguiça, Nuno
Databases are a fundamental component of any web service, storing and managing all the
service data. In large-scale web services, it is essential that the data storage systems used
consider techniques such as partial replication, geo-replication, and weaker consistency
models so that the expectations of these systems regarding availability and latency can
be met as best as possible.
In this dissertation, we address the problem of executing transactions on data that is
partially replicated. In this sense, we adopt the transactional causal consistency semantics,
the consistency model where a transaction accesses a causally consistent snapshot of the
database. However, implementing this consistency model in a partially replicated setting
raises several challenges regarding handling transactions that access data items replicated
in different nodes.
Our work aims to design and implement a novel algorithm for executing transactions
over geo-partitioned data with transactional causal consistency semantics. We discuss
the problems and design choices for executing transactions over partially replicated data
and present a design to implement the proposed algorithm by extending a weakly consistent
geo-replicated key-value store with partial replication, adding support for executing
transactions involving geo-partitioned data items. In this context, we also addressed the
problem of deciding the best strategy for searching data in replicas that hold only a part
of the total data of a service and where the state of each replica might diverge.
We evaluate our solution using microbenchmarks based on the TPC-H database. Our
results show that the overhead of the system is low for the expected scenario of a low
ratio of remote transactions.
Smart-contract Blockchain with Secure Hardware
Publication . Mendes, Diogo Alexandre Valente; Preguiça, Nuno
In recent years, blockchains have grown in popularity and the main reason for this
growth is the set of properties that they provide, such as user privacy and a public record
of transactions. This popularity is verifiable by the number of cryptocurrencies currently
available and by the current market value of Bitcoin currency. Since its introduction,
blockchain has evolved and another concept closely linked with it is smart-contract, which
allows for more complex operations over the blockchain than simple transactions.
Nevertheless, blockchain technologies have significant problems that prevent it to be
adopted as a mainstream solution, or at least as an alternative to centralized solutions
such as banking systems. The main one is its inefficiency, which is due to the need of a
consensus algorithm that provides total order of transactions. Traditional systems easily
solve this by having a single central entity that orders transactions, which can’t be done
in decentralized systems. Thus, blockchain’s efficiency and scalability suffer from the
need of time-costly consensus algorithms, which means that they can’t currently compete
with centralized systems that provide a much greater amount of transactional processing
power.
However, with the emergence of novel processor architectures, secure hardware and
trusted computing technologies (e.g. Intel SGX and ARM TrustZone), it became possible
to investigate new ways of improving the inefficiency issues of blockchain systems, by
designing better and improved blockchains.
With all this in mind, this dissertation aims to build an efficient blockchain system
that leverages trusted technologies, namely the Intel SGX. Also, a previous thesis will
serve as a starting point, since it already implements a secure wallet system, that allows
authenticated transactions between users, through the Intel SGX. As such, this wallet
system will be extended to provide traceability of its transactions through a blockchain.
This blockchain will use Intel SGX to provide an efficient causal consistency mechanism
for ordering transactions. After this, the following step will be to support the execution
of smart-contracts, besides regular transactions.
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Descrição
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Contribuidores
Financiadores
Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
9471 - RIDTI
Número da atribuição
PTDC/CCI-INF/32662/2017