SCARF – A Low-Latency Block Cipher for Secure Cache-Randomization


Federico Canale, Ruhr-University Bochum; Tim Güneysu, Ruhr-University Bochum and DFKI; Gregor Leander and Jan Philipp Thoma, Ruhr-University Bochum; Yosuke Todo, NTT Social Informatics Laboratories; Rei Ueno, Tohoku University


Randomized cache architectures have proven to significantly increase the complexity of contention-based cache side channel attacks and therefore present an important building block for side-channel secure microarchitectures. By randomizing the address-to-cache-index mapping, attackers can no longer trivially construct minimal eviction sets which are fundamental for contention-based cache attacks. At the same time, randomized caches maintain the flexibility of traditional caches, making them broadly applicable across various CPU-types. This is a major advantage over cache partitioning approaches.

A large variety of randomized cache architectures has been proposed. However, the actual randomization function received little attention and is often neglected in these proposals. Since the randomization operates directly on the critical path of the cache lookup, the function needs to have extremely low latency. At the same time, attackers must not be able to bypass the randomization which would nullify the security benefit of the randomized mapping. In this paper we propose SCARF (Secure CAche Randomization Function), the first dedicated cache randomization cipher which achieves low latency and is cryptographically secure in the cache attacker model. The design methodology for this dedicated cache cipher enters new territory in the field of block ciphers with a small 10-bit block length and heavy key-dependency in few rounds.

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@inproceedings {291015,
author = {Federico Canale and Tim G{\"u}neysu and Gregor Leander and Jan Philipp Thoma and Yosuke Todo and Rei Ueno},
title = {{SCARF} {\textendash} A {Low-Latency} Block Cipher for Secure {Cache-Randomization}},
booktitle = {32nd USENIX Security Symposium (USENIX Security 23)},
year = {2023},
isbn = {978-1-939133-37-3},
address = {Anaheim, CA},
pages = {1937--1954},
url = {},
publisher = {USENIX Association},
month = aug

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