Christian Cachin - IBM Research - Zurich Digital Security
Date: - Location: Eurecom
In the cloud computing model, the owner loses direct control over its data and programs. After outsourcing data to the cloud, the owner is bound to trust the cloud provider for confidentiality, privacy, integrity, and availability. However, cryptographic mechanisms can reduce such trust by allowing the owner to protect its data and programs. This presentation reviews some principles of cloud security and presents novel mechanisms for securing data in the cloud. Such techniques are the focus of current research projects at IBM Research - Zurich, in particular, (1) the integrity and consistency of remote data and (2) encryption mechanisms supporting policy-based secure deletion. The first project concerns multiple users that collaborate by accessing remote data. Existing cryptographic authentication can be readily used when only one user accesses the data; however, when multiple isolated users operate concurrently, then a malicious storage service may mount roll-back attacks and cause other inconsistencies, which cannot be prevented. Our approach achieves so-called forking consistency semantics when the server is faulty, which gives well-defined consistency guarantees to the users. The second project addresses the controlled erasure of data, as it has become difficult today to control the proliferation of data in storage systems. Operations to properly erase data and wipe out all its traces are typically not foreseen, particularly not in networked and cloud-storage systems. We discuss a general cryptographic model for policy-based secure deletion of data in storage systems, whose security relies on the proper erasure of cryptographic keys.