MTOTP: Wouldn't it be nice if you were the 2FA device?
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Re: MTOTP: Wouldn't it be nice if you were the 2FA device?
#2This is an early experiment in human-computable TOTP.
Not production crypto, but a serious attempt to reach reasonable security for plausible 2FA.
Protocol revisions, criticism, and contributions are welcome.
Re: MTOTP: Wouldn't it be nice if you were the 2FA device?
#3The idea is interesting, but I don't think this qualifies as a second factor, as it can be reduced to a factor you have to remember, so equivalent to a password. The second factor should be derived either from something you own, or something that can be obtained from biometry.
Re: MTOTP: Wouldn't it be nice if you were the 2FA device?
#4An interesting idea but in theory just three correct pass codes and some brute force will reveal the secret key so you'd have to be very careful about only inputting the pass code to sites that you trust well.
It's definitely computable on a piece of paper and reasonably secure against replay attacks.
Re: MTOTP: Wouldn't it be nice if you were the 2FA device?
#5What makes this 2FA? It's "something you know, plus mental labor", which makes it a password.
2FA is "something you have" (or ".. you are", for biometrics): it is supposed to prove that you currently physically posses the single copy of a token. The textbook example is a TOTP stored in a Yubikey.
Granted, this has been watered down a lot by the way-too-common practice of storing TOTP secrets in password managers, but that's how it is supposed to work.
Does your mTOTP prove you own the single copy? No, you could trivially tell someone else the secret key. Does it prove that you currently own it? No, you can pre-calculate a verification token for future use.
I still think it is a very neat idea on paper, but I'm not quite seeing the added value. The obvious next step is to do all the math in client-side code and just have the user enter the secret - doing this kind of mental math every time you log in is something only the most hardcore nerds get excited about.
Re: MTOTP: Wouldn't it be nice if you were the 2FA device?
#6Isn't this just manually hashing a password with a timed-salt? I don't see how this relates to TOTP
Re: MTOTP: Wouldn't it be nice if you were the 2FA device?
#7What makes this 2FA? It's "something you know, plus mental labor", which makes it a password. 2FA is "something you have" (or ".. you are", for biometrics): it is supposed to prove that you currently physically posses the single copy of a token. The textbook example is a TOTP stored in a Yubikey. Granted, this has been watered down a lot by the way-too-common practice of storing TOTP secrets in password managers, but…
Time based skew makes it a changeable second factor,
additional changeable pass makes it the second factor,
Also - if the first factor is a password manager or ssh key - this is the second factor.
The idea of it was so neat to me, I just had to thinker with it.
Re: MTOTP: Wouldn't it be nice if you were the 2FA device?
#8Isn't this just manually hashing a password with a timed-salt? I don't see how this relates to TOTP
TOTP is also just hashing a password with a time salt. The purpose is just to prove that you are in possession of the device that stores the password without actually ever entering the password anywhere where it can be leaked. In this case the device is just your brain.
Re: MTOTP: Wouldn't it be nice if you were the 2FA device?
#9What makes this 2FA? It's "something you know, plus mental labor", which makes it a password. 2FA is "something you have" (or ".. you are", for biometrics): it is supposed to prove that you currently physically posses the single copy of a token. The textbook example is a TOTP stored in a Yubikey. Granted, this has been watered down a lot by the way-too-common practice of storing TOTP secrets in password managers, but…
In practice most TOTP implementation also do not prove that you have a device which is the sole owner of the secret. Except for proprietary app-based solutions the usual protocol is to display a QR code which just encodes the secret in plain text.
As long as you never enter the secret anywhere but only do the computation is your head, this is just using your brain as the second factor. I would not call this a password since it is not used in the same way. Passwords are entered in plain text into fields that you trust, but that also means that passwords can be stolen. This proves that you are in possession of your brain.
Re: MTOTP: Wouldn't it be nice if you were the 2FA device?
#10An interesting idea but in theory just three correct pass codes and some brute force will reveal the secret key so you'd have to be very careful about only inputting the pass code to sites that you trust well. It's definitely computable on a piece of paper and reasonably secure against replay attacks.
Yep, I am aware, 2 or 3 OTP's and timestamps plus some brute forcing using the source-code. Server-side brute force by input should or could be implausible.
But that is why I am signaling here that I would love a genius or a playful expert/enthusiast contributing a bit or two to it - or becoming a co-author.