Securing Data Accountability in Decentralized Systems

We consider a decentralized setting in which agents exchange data along with usage policies. Agents may violate the policies, although later on auditing authorities may verify the agents' accountability with respect to the used data. Using (provably secure) time-stamping and signature schemes, we design and analyze an efficient cryptographic protocol that generates the sufficient communication evidences which auditing authorities need to carry out their auditing. Finally, we describe an extension providing policy confidentiality against eavesdroppers timestamping servers.