Last week a researcher outlined what he said was a “novel attack surface” in passkeys, the new authentication paradigm that offers a more secure alternative over password-based methods. In fact, the attacks demonstrated in the post are neither novel nor unique to passkeys. This distinction is important because the research has generated confusion among end users and security professionals as they assess whether this new mechanism is truly safe to use.
The attack is called Pass-ta-key—a blending of the word passkey with the phrase “pass the key” and a nod to a plate of pasta. Arie Olshtein, a researcher at security firm Palo Alto Networks, described in a post last week how Pass-ta-key could obtain all passkeys stored in the Google Password Manager app (GPM) for Windows when it’s running on a machine infected with malware.
This came as a surprise to many people because they believed passkeys are stored exclusively in the trusted platform manager (TPM), the locked-down enclave in a hardened silicon chip that’s reserved for storing cryptographic keys and other highly sensitive information on Windows machines. If passkeys are stored in the TPM, then how was Pass-ta-key able to extract the entire set of passkeys stored by the app, they wanted to know?
Local passkey storage is OK, with one exception
The answer is that, contrary to common belief, the FIDO 2 specifications—managed by the industry group FIDO Alliance—don’t mandate that passkeys be kept in TPMs, or any other sort of dedicated piece of hardware (they go by different names, depending on the platform, including secure enclaves, trusted execution environments, and StrongBoxes). In fact, most platforms and third-party software for managing passkeys do not store passkeys in such dedicated hardware. Virtually the lone holdout is Microsoft, which gives users the option to store passkeys in the Windows TPM. The company mainly recommends this choice to enterprises, not consumers.