<oai_dc:dc xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:oai_dc="http://www.openarchives.org/OAI/2.0/oai_dc/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/oai_dc/ http://www.openarchives.org/OAI/2.0/oai_dc.xsd">
  <dc:contributor>Pedone, Fernando</dc:contributor>
  <dc:creator>Fynn, Enrique</dc:creator>
  <dc:date>2021-02-09</dc:date>
  <dc:description xmlns:ns0="xml" ns0:lang="en">Blockchains are a new type of state machine replication that have raised interesting challenges. A replicated state machine (RSM) is a  well-established approach to building fault-tolerant systems. Because each replica needs to execute the same set of instructions to  transition through the same state changes, adding more replicas does not translate directly to an increase in performance. On top of  that, RSM can be made to tolerate Byzantine failures, i.e., nodes in the system can have arbitrary behavior. Blockchains distinguish  themselves from traditional RSM mainly for having an open membership, being decentralized, and involving economic aspects as a  means to counter adversarial attacks. Yet, despite their increasing popularity, current blockchain systems scale poorly and are  constrained to exist in isolation, unable to communicate with each other. In this thesis, we explore techniques to make blockchains  scale in two angles: (a) scaling blockchain transaction throughput; and (b) making the state synchronization faster and robust for  incoming peers. For (a), we analyze the effects of partitioning a real blockchain state in several shards and how to minimize  communication within shards, while keeping the shards balanced. We then propose a protocol that can be applied to increase the  throughput of a sharded blockchain or by which blockchains can communicate with each other. For (b), we propose a data structure  that can be used by blockchains to enhance scalability by easing the synchronization process and allowing the blockchain’s state to be  reconstructed without requiring additional trust. The claims in this thesis are sustained by extensive experimental evaluation using real  applications from public blockchains, developing new protocols and algorithms, and performing tests in geo-replicated environments.</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>https://susi.usi.ch/global/documents/319287</dc:identifier>
  <dc:identifier>https://localhost:5000/ark:/12658/srd1319287</dc:identifier>
  <dc:identifier>https://susi.usi.ch/documents/319287/files/2021INFO003.pdf</dc:identifier>
  <dc:language>eng</dc:language>
  <dc:relation>info:eu-repo/semantics/altIdentifier/urn/urn:nbn:ch:rero-006-119159</dc:relation>
  <dc:relation>info:eu-repo/semantics/altIdentifier/ark/12658/srd1319287</dc:relation>
  <dc:rights>info:eu-repo/semantics/openAccess</dc:rights>
  <dc:rights>License undefined</dc:rights>
  <dc:subject xmlns:ns1="xml" ns1:lang="en">Blockchain</dc:subject>
  <dc:subject xmlns:ns2="xml" ns2:lang="en">Smart contract</dc:subject>
  <dc:subject xmlns:ns3="xml" ns3:lang="en">Inter-blockchain transaction</dc:subject>
  <dc:subject>info:eu-repo/classification/udc/004</dc:subject>
  <dc:title xmlns:ns4="xml" ns4:lang="en">Scaling blockchains</dc:title>
  <dc:type>http://purl.org/coar/resource_type/c_db06</dc:type>
</oai_dc:dc>