Abstract In practice, there are numerous settings where mutually distrusting parties need to perform distributed computations on their private inputs. For instance, participants in a first-price sealed-bid online auction do not want their bids to be disclosed. This problem can be addressed using secure multi-party computation (MPC), where parties can evaluate a publicly known function on their private inputs by executing a specific protocol that only reveals the correct output, but nothing else about the private inputs. Such distributed computations performed over the Internet are susceptible to remote hacks that may take place during the computation. As a consequence, sensitive data such as private bids may leak. All existing MPC protocols do not provide any protection against the consequences of such remote hacks. We present the first MPC protocols that protect the remotely hacked parties’ inputs and outputs from leaking. More specifically, unless the remote hack takes place before the party received its input or all parties are corrupted, a hacker is unable to learn the parties’ inputs and outputs, and is also unable to modify them. We achieve these strong (privacy) guarantees by utilizing the fact that in practice parties may not be susceptible to remote attacks at every point in time, but only while they are online, i.e. able to receive messages. To this end, we model communication via explicit channels. In particular, we introduce channels with an airgap switch (disconnect-able by the party in control of the switch), and unidirectional data diodes. These channels and their isolation properties, together with very few, similarly simple and plausibly remotely unhackable hardware modules serve as the main ingredient for attaining such strong security guarantees. In order to formalize these strong guarantees, we propose the UC with Fortified Security (UC#) framework, a variant of the Universal Composability (UC) framework.

Outsourcing data processing and storage to the cloud is a persistent trend in the last years. Cloud computing offers many advantages like flexibility in resource allocation, cost reduction and high availability. However, when sensitive information is handed to a third party, security questions are raised since the cloud provider and his employees are not fully trusted. Standard security mechanisms like transport encryption and regular audits alone cannot solve the issue of insider attacks. Additional cryptographic techniques are required. In this paper, we build upon an existing proxy for secure database outsourcing. We address potential side-channels and weaknesses, which are later analyzed and mitigated. Furthermore, we take a look at trusted execution environments (TEEs) like Intel Software Guard Extensions (SGX) and show how they can be applied to allow for secure execution in the secure database outsourcing case.

Cloud computing offers many advantages as flexibility or resource efficiency and can significantly reduce costs. However, when sensitive data is outsourced to a cloud provider, classified records can leak. To protect data owners and application providers from a privacy breach data must be encrypted before it is uploaded. In this work, we present a distributed key management scheme that handles user-specific keys in a single-tenant scenario. The underlying database is encrypted and the secret key is split into parts and only reconstructed temporarily in memory. Our scheme distributes shares of the key to the different entities. We address bootstrapping, key recovery, the adversary model and the resulting security guarantees.