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Comment by u801e | Hacker News Reader

Unfortunately, MFA has become synonymous with SMS, email, and OTP. All of these methods require sharing a secret between two parties without any way to verify the authenticity of either party.

Key based authentication where both parties have private keys that are not shared is a much better alternative. Unfortunately, client side TLS certificates, which are application level protocol agnostic, never really caught on.

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There is U2F/FIDO keys / passkeys which are what you describe, latter just very recently becoming widely available. When/if they become successful is another question. U2F/FIDO etc keys are only supported by a subset of websites.

> U2F/FIDO etc keys are only supported by a subset of websites.

But a growing number. https://passkeys.directory/ is a good place to check.

Ask for it. MFA via SMS/email/etc was not very common 10 years ago, but it is now. That's due in part to people asking for it.

But they're not application level protocol agnostic. Based on my understanding, they require use of HTTP. If I want to get MFA using an email client communicating via SMTP and IMAP, then the email client needs to be able to interact with the HTTP API.

You can use FIDO tokens for other protocols: I use it for SSH, for example since OpenSSH 8.2 or so.

That requires the client to implement FIDO support. This was added to openssh 8.2p1. For example, mutt doesn't have FIDO support and you have to use an external script for oauth2 support. Both require implementing support for interacting with a HTTP API (which is not application level protocol agnostic).

On the other hand, you can configure mutt to use a client side TLS certificate and SMTP servers (e.g., postfix) and IMAP servers (e.g. dovecot) both support client side TLS certificates without having to support sending HTTP requests or parsing HTTP responses.

It’s not HTTP - the design uses a much smaller binary protocol (hardware tokens are very constrained) called CTAP:

https://fidoalliance.org/specs/fido-v2.0-id-20180227/fido-cl...

OpenSSH uses that protocol to request encryption operations. Mutt could do that the same way but it’d need a server which supports the same crypto algorithm FIDO2 specifies. That’d be great but also somewhat pointless if you’re using Yubikeys which support x509 auth which IMAP and SMTP have supported for decades.

Client side tls certificates are the worst of all the options. They only make sense fully managed or for server to server communication.

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