Randomized Data Can Improve Our Security

Innovative Mathematical Solution
While patches have been developed to fix the vulnerability for certain attacks, they have failed to provide provable security. However, the team from Bochum and Japan has now come up with an innovative solution: “Our idea is to use mathematical processes to randomize the data in the cache,” explains Gregor Leander, who recently received an ECR Advanced Grant for his research. This randomization in the CPU’s caches can help prevent attacks by disabling attackers from removing data from the cache.

The interdisciplinary approach of cryptography and hardware security considerations is a novelty in computer security. While there have been previous ideas for randomized cache architectures, none have been very efficient and none have been able to completely withhold strong attackers,” said Tim Güneysu, who heads the Chair of Security Engineering. The new SCARF modeluses block cipher encryption, a completely new idea for the field, according to the researchers.

Normally, we encrypt data with 128 bits, in the cache we sometimes work with 10 bits. This is a complex process because it takes much longer to mix this data with a large key,” said Gregor Leander. The large key is needed because a shorter encryption of such small amounts of data could be more easily broken by attackers.

The aforementioned randomization usually takes a lot of time. This would limit the functionality of the cache. In contrast, SCARF uses block ciphers to operate faster than any previous solution. “SCARF can be used as a modular component in cache architectures and automatically ensures secure—i.e. unpredictable—randomization with simultaneously low latency, i.e. response time,” explains Jan Philipp Thoma: “He concludes: “With SCARF, we offer an efficient and secure solution for randomization.”

Double Protection by Combining with ClepsydraCache
The work done by the researchers can therefore have a fundamental impact on protecting sensitive data in the digital society. In addition, the researchers, in collaboration with other colleagues, present another work at this year’s Usenix Security Symposium that can be combined with SCARF.

The paper, “ClepsydraCache—Preventing Cache Attacks with Time-Based Evictions,” likewise introduces a new idea for cache security. Jan Philipp Thoma, Gregor Leander, Tim Güneysu and CASA PI Lucas Davi from the University of Duisburg-Essen are also involved.

It was also developed in close collaboration with researchers from the Department of Integrated Systems at RUB. “ClepsydraCache relies on cache decay combined with index randomization. Cache decay means that data that is not used for a longer period of time is automatically removed from the cache,” explains Jan Philipp Thoma.

Data security benefits from such a mechanism, as it reduces the number of cache conflicts. Those conflicts would slow down the process and might also lead to data leakage with the help of the side-channel attacks described above. The researchers were able to prove that their proposal can withstand known attack vectors and can be easily implemented in existing architectures.

Interdisciplinary Work leads to Successful Research
The compatibility of the two “SCARF” and “Clepsydracache” works could therefore make future generations of caches more secure than ever before—without affecting their performance in any way. The teamwork thus shows that the interdisciplinary approach pursued by the Cluster of Excellence CASA “Cybersecurity in the Age of Large-Scale Adversaries” can lead to groundbreaking research results.