Cloud computing aims at flexible and scalable infrastructures using virtualized resources. Although virtualization and outsourcing improve efficiency and flexibility, they also introduce new threats.

Cryptography is only as good as the keys used.

—Elli Androulaki, IBM scientist

We mitigate these threats by means of new security technologies to protect virtual environments. Moreover, we are designing novel mechanisms that provide protection levels beyond those of today’s non-virtualized systems.

Whereas providers employ traditional security measures, clients of cloud services can use cryptography to provide additional protection to their data. Data encryption and integrity protection methods give clients some degree of control over their data, but crucial aspects must still be addressed:

  • Cryptography is only as good as the keys used. Hence one needs good solutions for key management.
  • As encrypting data prevents data from being processed in the cloud, additional sophisticated cryptographic schemes are needed to enable limited processing.

With its strong background in cryptography and system security, our team has made key contributions to research, products and standards in the domain of cloud and data security.

Research projects



This project focuses on the fact that most security protocols/schemes either provide security at the expense of the economy of scale and cost effectiveness of the cloud, or they meet the latter objectives at the expense of security.

The TREDISEC project addresses this issue by developing systems and techniques to make the cloud a secure and efficient haven to store data.

The project will devise, analyse, and implement a set of cloud security primitives to ensure the confidentiality and integrity of outsourced data in the presence of a powerful attacker who controls the entire network.



This project aims to empower data owners as first-class citizens of the cloud.

ESCUDO-CLOUD provides effective and deployable solutions allowing data owners to maintain control over their data when relying on Cloud Service Providers (CSPs) for data storage, processing and management without sacrificing functionality.



This project is producing a framework for end-to-end (E2E) protection of data in untrusted and fast evolving ICT-based environments.

The WITDOM projects focuses in particular on data-outsourcing scenarios, where new threats, vulnerabilities and risks due to new uses require end-to-end security solutions that will withstand progress for the lifetime of applications they support.



This project is researching and developing a new security and dependability infrastructure management paradigm.

On the one hand, our approach is user-centric for self-service clouds-of-clouds. In other words customers can define their own protection requirements and avoid provider lock-ins.

On the other hand, we are focusing on self-managed services to self-protect clouds-of-clouds. This is expected to reduce administration complexity by means of automation.

Integrity and consistency verification

Towards reducing the dependency of users on remote cloud services, we develop methods for the verification of integrity and consistency for cloud services. We address a remote, untrusted cloud accessed by multiple users collaborating with each other using the cloud. Users do not usually communicate with each other, but may do so in exceptional situations.

Traditional cryptography can protect against all attacks except for violations of consistency, where the cloud attempts to hide operations executed by some clients in the views of other clients.

We have discovered fundamental mechanisms for mitigating such attacks and developed protocols that provide the best-possible integrity guarantees in this scenario, so-called forking consistency properties. One of these protocols is implemented in VICOS, a prototype that adds verification of data-integrity and consistency to any cloud object-storage service.

Key management and secure deletion

Key management is the Achilles heel of a cryptographic system, especially for data encryption in the cloud. Cloud storage systems rely on master encryption keys that are maintained reliably and securely.

To support this goal we have designed and contributed code to many key-management standards and systems, including the OASIS Key Management Interoperability Protocol (KMIP), the IBM Security Key Lifecycle Manager, for encryption in IBM Spectrum Scale, and Data Encryption in OpenStack Swift storage.

Our work focuses on strong cryptography, high assurance, and compatibility with enterprise environments. Flexible key-management solutions also provide a way to securely delete data, by destroying only the corresponding keys. For protecting against residual information remaining on storage devices and being exposed after it should have been removed, our policy-based secure deletion systems use protected master encryption keys and erase data securely.


C. Cachin, E. Ghosh, D. Papadopoulos, B. Tackmann,
Stateful Multi-Client Verifiable Computation,”
Cryptology ePrint Archive.

G. Karame, M. Neugschwandtner, M. Önen, H. Ritzdorf,
Reconciling Security and Functional Requirements in Multi-tenant Clouds,”
in Proc. 5th ACM Int’l Workshop on Security in Cloud Computing, 2017.

R. Di Pietro, A. Sorniotti,
Proof of ownership for deduplication systems: A secure, scalable, and efficient solution,”
Computer Communications 82, 71-82 (2016).

M. Brandenburger, C. Cachin, and N. Knezevic,
Don’t trust the cloud, verify: Integrity and consistency for cloud object stores,”
in Proc. 8th ACM Int’l Systems and Storage Conference (SYSTOR), 2015.

C. Cachin and O. Ohrimenko,
Verifying the consistency of remote untrusted services with commutative operations,”
in Proc. 18th Int’l Conference on Principles of Distributed Systems (OPODIS), 2014.

N. Baracaldo, E. Androulaki, J. Glider, A. Sorniotti,
Reconciling End-to-End Confidentiality and Data Reduction In Cloud Storage,”
in Proc. ACM Workshop on Cloud Computing Security (CCSW), 2014.

D. Dobre, P. Viotti, M. Vukolic,
Hybris: Robust Hybrid Cloud Storage,”
in Proc. ACM Symposium on Cloud Computing (SoCC), 2014.

C. Cachin, K. Haralambiev, H.-C. Hsiao, and A. Sorniotti,
Policy-based secure deletion,”
in Proc. 20th ACM Conference on Computer and Communications Security (CCS), 2013.

J. Bringer, B. Gallego-Nicasio, G. Karame, M. Kohler, P. Louridas, M. Önen, H. Ritzdorf, A. Sorniotti, D. Vallejo,
TREDISEC: Trust-Aware REliable and Distributed Information SEcurity in the Cloud,”
in Proc. Int’l Conference on e-Democracy – Citizen Rights in the World of the New Computing Paradigms, Springer, 193-197, 2015.

J. Blasco Alís, R. Di Pietro, A. Orfila, A. Sorniotti,
A tunable proof of ownership scheme for deduplication using Bloom filters,”
in Proc. IEEE Conference on Communications and Network Security (CNS), 481-489, 2014.

J. Stanek, A. Sorniotti, E. Androulaki, L. Kencl,
A Secure Data Deduplication Scheme for Cloud Storage,”
Financial Cryptography, 99-118, 2014.

R. Di Pietro, A. Sorniotti,
Boosting efficiency and security in proof of ownership for deduplication,”
in Proc. 7th ACM Symp. on Information, Computer and Communications Security (ASIACCS), 81-82, 2012.

A. Kurmus, M. Gupta, R. Pletka, C. Cachin, R. Haas,
A Comparison of Secure Multi-tenancy Architectures for Filesystem Storage Clouds,”
in Proc. ACM/IFIP/USENIX 12th International Middleware Conference, December 2011.