> Are non-resident keys less secure? The answer provided by the author (TLDR: you'd have to break AES) is far from satisfying to me. With a resident key, the

> Are non-resident keys less secure? The answer provided by the author (TLDR: you'd have to break AES) is far from satisfying to me. With a resident key, the only thing an attacker on an endpoint could ever get is a challenge & a response to that challenge. It's more than nothing, but limits a lot of attacks. With non-resident keys, an attacker can not only do all kinds of offline attacks* against the HMAC and crypto, but also has a far better position of attack against the the security key: you've got decryption, HMAC, key parsing code all happening on untrusted data (if done correct, HMAC will have to fall first). Further, you've got twice the encryption happening on the key, which could provide a larger attack surface for side channel attacks. I'm not saying any of these are trivial or even feasible, just that "citation needed" for resident key == non-resident key, in terms of security. *if your idea of an offline attack of this nature is "break AES with a brute force" and that's about it, there's a lot more options