Cryptography & Security Newsletter

Hertzbleed shows how CPU frequency scaling can lead to side-channel attacks

30 Jun 2022

Feisty Duck’s Cryptography & Security Newsletter is a periodic dispatch bringing you commentary and news surrounding cryptography, security, privacy, SSL/TLS, and PKI. It's designed to keep you informed about the latest developments in this space. Enjoyed every month by more than 50,000 subscribers. Written by Hanno Böck.

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A new type of side-channel vulnerability called Hertzbleed was published recently. The attack relies on dynamic frequency scaling, a power-saving and performance feature on modern CPUs.

What the authors discovered is that certain CPU operations can lead to frequency changes depending on the processed data. This makes common constant-time programming methods insufficient to mitigate this type of attack.

The Hertzbleed authors were able to demonstrate their attack against SIKE, a post-quantum algorithm based on supersingular isogenies. But it should be noted that the attack is more generic, and it’s expected that variations of it may impact other cryptographic algorithms.

According to the authors, a possible mitigation to Hertzbleed is to disable frequency boosting features on CPUs. On Intel CPUs, this feature is called Turbo Boost; on AMD, it’s called Turbo Core or Precision Boost. It's possible to disable these features via BIOS settings or via the operating system, but it will cause a slowdown of the system.

In response to the attack Daniel Bernstein has created a webpage with links to research and resources about timing attacks.

A mitigation for the specific attack on SIKE is also available. A previous research paper, published in January, has already identified a power side-channel that works similarly to the attack the Hertzbleed authors demonstrated, and the mitigation proposed in that paper works here as well. However, it adds a significant overhead of between 5 and 11 percent to the already slow SIKE algorithm.

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