alt Hacker NewsThe single copy part would be a lot more common if it was widely supported to have multiple tokens registered to an account.
And the main point (though I agree that it doesn't make it 2FA), is to not have the secret be disclosed when you prove that you have it, which is what TOTP also achieves, which makes phishing or sniffing it significantly less valuable.
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I guess it's a spectrum. At one extreme is the most physically resistant hardware token in existence. On the other end is a password transmitted in plaintext.
An ssh keyfile requires an attacker to break into the device but is likely fairly easy to snag with only user level access.
Bypassing a password manager that handles TOTP calculations or your ssh key or similar likely requires gaining root and even then could be fairly tricky depending on the precise configuration and implementation. That should generally be sufficient to necessitate knowledge of the master password plus device theft by an insufficiently sophisticated attacker.
Given TOTP or an ssh key managed exclusively by a hardware token it will be all but impossible for anyone to avoid device theft. Still, even TPMs have occasionally had zero day vulnerabilities exposed.
Are there any mainstream websites which only allow a single TOTP token to be enrolled? I can't remember having ever run into that issue. I do recall it occasionally being an issue with Passkeys, though.
The non-disclosure is indeed neat, but the same can be achieved with a password. For example: generate public/private keypair on account creation. Encrypt private key with user password. Store both on server. On auth, client downloads encrypted priv key, decrypts it with user-entered password, then signs nonce and provides it to server as proof of knowledge of user password.