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Practical Active Revocation

We propose Knob, a practical active revocation scheme allowing to efficiently revoke users' access to encrypted data banks stored in public clouds. Knob leverages Trusted Execution Environments and All-or-Nothing Data Transforms in order to re-encrypt only small portions of the content directly in the cloud, using a scalable swarm of re-encryption workers. It prevents malicious users from being able to predict which portions of the files will be re-encrypted upon a revocation, effectively disabling pre-provisioning attacks. Our evaluation using industry workloads shows that Knob outperforms active revocation using full re-encryption by up to 3 orders of magnitude while being on average 3 to 7 times faster than state-of-the-art partial re-encryption.