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Comment by ACCount37

1 month ago

TOTP is the "good enough" 2FA.

If I managed to intercept a login, a password and a TOTP key from a login session, I can't use them to log in. Simply because TOTP expires too quickly.

That's the attack surface TOTP covers - it makes stealing credentials slightly less trivial by making one of the credentials ephemeral.

3 comments

ACCount37

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alphager  1 month ago

The 30 seconds (+30-60 seconds to account for clock drift) are long enough to exploit.

TOTP is primarily a defense against password reuse (3rd party site gets popped and leaks passwords, thanks to TOTP my site isn't overrun by adversaries) and password stuffing attacks.

  • vel0city  1 month ago

    In every system I've worked on recent successful TOTPs have been cached as well to validate they're not used more than once.

    • vel0city  1 month ago

      In fact, re-reading RFC 6238 it states:

         Note that a prover may send the same OTP inside a given time-step
   window multiple times to a verifier.  The verifier MUST NOT accept
   the second attempt of the OTP after the successful validation has
   been issued for the first OTP, which ensures one-time only use of an
   OTP.

      https://datatracker.ietf.org/doc/html/rfc6238

      Assuming your adversary isn't actually directly impersonating you but simply gets the result from the successful attempt a few seconds later, the OTP should be invalid, being a one time password and all.