EUCLEAK Side-Channel Attack on the YubiKey 5 Series

Website & Resources

• Several people report the Ninjalab site hanging; workarounds include reader mode, blocking the loading overlay, or using the linked PDF.
• Links to Yubico’s advisory and support article are shared.

Vulnerability Scope & Requirements

• Affects YubiKey 5 series with firmware <5.7 using Infineon’s cryptographic library.
• Exploit is an electromagnetic side-channel on a non-constant-time modular inversion in ECDSA.
• Requires physical access, disassembly of the key, lab-grade EM equipment, and a few minutes of traces.
• Once refined, the attack might not require fully destroying the device; current work didn’t focus on re-packaging.

Impact on Security Guarantees

• Key extraction turns the device from “unextractable secrets” into “very hard-to-extract secrets”.
• Some argue this is mainly a high-end, targeted attack; others note many YubiKey use cases (crypto, defense, banking) are exactly such high-value targets.
• Attestation keys can also be cloned, undermining hardware model enforcement and FIDO attestation in some deployments.

Firmware, Mitigations & Replacement Debate

• YubiKey firmware is not upgradable; old devices remain vulnerable.
• Earlier Infineon issue (ROCA) led to free replacements; several posters are surprised replacements aren’t offered now.
• YubiKey 5.7 switches from Infineon to Yubico’s own crypto library; some are nervous about custom crypto, others say it’s reasonable after multiple vendor failures.

Broader Infineon Ecosystem

• Discussion notes all Infineon secure microcontrollers using the affected crypto library may be vulnerable: TPMs, e-passports, phone secure enclaves, SIMs, some hardware wallets, EMV cards, tachographs, etc.
• There’s debate about how serious this is for each: some see primarily forensic/government use; others highlight passports, banking apps, and payment systems as significant.

FIDO2, PINs, UV & Passkeys

• PIN/user verification can often be bypassed because relying parties may request “user verification not required”; thus the side-channel can be driven without PIN knowledge.
• This can reduce “key + PIN” from two factors to effectively one (possession).
• Resident (discoverable) vs non-resident credentials matter: resident ones can be attacked offline; non-resident need the credential ID, typically learned via a legitimate challenge.

Usability, Backups & Account Management

• Major pain point: no easy way to enumerate where a key is registered; users resort to tagging entries in password managers.
• Many recommend registering multiple keys only on critical services (email, password manager, SSO, cloud) and keeping backups in separate locations.
• Some lament difficulty of securely backing up or cloning keys; proposals for paired/synchronizable keys are debated as too risky/complex.

Crypto Engineering & Certification Critique

• Infineon is criticized for a non-constant-time primitive; modular inversion leaks are seen as a basic failure.
• Common Criteria certifications are questioned since the flaw survived ~14 years and many evaluations.
• Some note this is a known class of attacks; constant-time algorithms, blinding, or using schemes like EdDSA could have mitigated it.