In the last lesson, you sorted proof from not-proof. Here is the pattern you were already using: most login proofs you use directly are a thing you know, a thing you have, or a thing you are.
Security folks draw these as the three corners of a triangle. It looks like this.
Information stored in your head: a password, a PIN (Personal Identification Number), or the answer to a secret question. It travels with you everywhere and weighs nothing.
A device or recovery item you control: your phone receiving a text, an authenticator app creating a code, a security key, or printed backup codes stored safely. These show that you have access to something connected to the account.
A part of your body: your fingerprint, your face, or your voice. Using your body as a key is called biometrics.
Say it: bi-oh-MET-riks.
Because the corners are strongest together. A password can be guessed. Your phone might get left on the bus. And a fingerprint reader does not always recognize a cold thumb.
No single corner is perfect, and that is fine. The plan was never to rely on one corner. The next two lessons show how the corners back each other up: first to keep strangers out, then to let you back in.
Time to practice. For each one below, pick the corner it belongs to.
One lock is a suggestion. Two locks are a wall. Continue to Two locks are better than one.