9 minOct 30, 2026
Two-Factor Authentication Will Finally Make Sense
Two-factor authentication (2FA), for complete beginners, on four real Linux machines in our lab: Ana's shop server, her laptop, a stand-in for her phone, and a thief who has her password from a leaked list. With only a password, the thief logs straight in. We set up an authenticator, see how a phone with no network makes exactly the same six-digit code as the server (TOTP: a shared secret plus the time), turn two-factor on for SSH, and watch the same leaked password fail, even with a code the thief saw seconds ago. Then: text messages vs app codes vs push vs security keys and passkeys, and what to do if you lose your phone.
