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This paper presents on-going research to develop the

International audienceTo preserve the Bitcoin ledger’s integrity, a node that joins the system must download a full copy of the entire Bitcoin blockchain if it wants to verify newly created blocks.At the time of writing, the blockchain weights 79 GiB and takes hours of processing on high-end machines. Owners of low-resource devices (known as thin nodes), such as smartphones, avoid that cost by either opting for minimum verification or by depending on full nodes, which weakens their security model.In this work, we propose to harden the security model of thin nodes by enabling them to verify blocks in an adaptive manner, with regards to the level of targeted confidence, with low storage requirements and a short bootstrap time. Our approach exploits sharding within a distributed hash table (DHT) to distribute the storage load, and a few additional hashes to prevent attacks on this new system

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Cloud computing gives users much freedom on where they host their computation and storage. However the CO 2 emission of a job depends on the location and the energy efficiency of the data centers where it is run. We developed a decision framework that determines to move computation with accompanying data from a local to a greener remote data center for lower CO 2 emissions. The model underlying the framework accounts for the energy consumption at the local and remote sites, as well as of networks among them. We showed that the type of network connecting the two sites has a significant impact on the total CO 2 emission. Furthermore, the task's complexity is a factor in deciding when and where to move computation.

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