  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 some 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 a practical
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 beyond legacy TLS cipher
suites. Using HyperDegrade we developed an end-to-end attack that shows how a
Raccoon-like attack can succeed in practice, filling a missing gap from
previous research.
