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Take Control of Your Passwords, 3rd Edition by Joe Kissell

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Appendix A: Use Two-Factor Authentication

Earlier, in Multi-Factor Authentication and Manage Email Options, I said that some companies enable (or require) you to use a combination of factors—things you know, things you have, and things you are—to prove your identity. In the most common implementation, one factor is your password (a thing you know) and the second is an object (a thing you have). The result is two-factor authentication (2FA).

A variation on this process requires your regular password plus a time-limited, one-time password (OTP); that password is generated by an app or sent to you via SMS or email. Because the OTP is still, strictly speaking, something you know—and because a single device could unlock your password and display ...

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