  Performance degradation techniques are an important complement to
side-channel attacks. In this work, we propose HyperDegrade -- a combination of
previous approaches and the use of simultaneous multithreading (SMT)
architectures. In addition to the new technique, we investigate the root causes
of performance degradation using cache eviction, discovering a previously
unknown slowdown origin. The slowdown produced is significantly higher than
previous approaches, which translates into an increased time granularity for
Flush+Reload attacks. We evaluate HyperDegrade on different Intel
microarchitectures, yielding significant slowdowns that achieve, in select
microbenchmark cases, three orders of magnitude improvement over
state-of-the-art. To evaluate the efficacy of performance degradation in
side-channel amplification, we propose and evaluate leakage assessment metrics.
The results evidence that HyperDegrade increases time granularity without a
meaningful impact on trace quality. Additionally, we designed a fair experiment
that compares three performance degradation strategies when coupled with
Flush+Reload from an attacker perspective. We developed an attack on an
unexploited vulnerability in OpenSSL in which HyperDegrade excels -- reducing
by three times the number of required Flush+Reload traces to succeed. Regarding
cryptography contributions, we revisit the recently proposed Raccoon attack on
TLS-DH key exchanges, demonstrating its application to other protocols. Using
HyperDegrade, we developed an end-to-end attack that shows how a Raccoon-like
attack can succeed with real data, filling a missing gap from previous
research.
