The Hardware and Embedded Systems practice of NCC Group had cause to delve into some particularly crafty EM side-channel work in late 2024, thanks to a request to duplicate the Eucleak vulnerability.
The original research (https://ninjalab.io/eucleak/) performed by Thomas Roche and others at NinjaLab in Quebec, demonstrated a long-standing subtle information leak in the Infineon secure element used in the YubiKey 5 Series products, and many other devices using that chip. By exploiting it, they demonstrated it was possible to extract the secret ECDSA key, which would enable cloning of the hardware token, and entirely destroy that root of trust. Thankfully, Infineon quickly patched the vulnerability, and YubiKeys with firmware 5.7+ are no longer vulnerable.
In this paper, we describe the steps we took to successfully replicate this attack in a period of two weeks, using lab-fabricated equipment and a number of expediencies.