HN

Comments (95)

• Menu

  crote
  What 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.
• EPWN3D
  If you can be tied to a chair and beaten with a rubber hose until you produce the token, it's just a password, albeit one that rotates.TOTP works because you have to possess the secure device at the time you're authenticating. If you don't have the device, then no amount of time with the rubber hose can make you cough up the required token.
• Menu

  barbegal
  An 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.
• Menu

  brna-2
  This 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.
• istillwritecode
  No. I'm comfortable remembering passwords.
• Menu

  jrm4
  So, in my head, once I heard the idea, I started thinking of something WAY different, and maybe its worth considering. I was thinking something like a combination "security question," "captcha" and "secondary identifier" (whatever the thing that google et al do when they tell you to match the picture on your phone to complete the login)I don't know, something like "name the fruits that correspond to your first school colors" or similar
• perching_aix
  I've been pondering about something like this for a while, nice to see someone who didn't give up after seeing how demanding actual crypto is, like I did.I now wonder if it's possible to store a random value in one's head without it being eavesdroppable. Humans don't really do random, but it's essential for auth.
• pona-a
  Yes! I've been thinking about a similar idea in October, using a "keyed hash" of the challenge computed with playing cards. I have no idea how secure this is, but the concept itself is exciting: the mental labor might function as a useful anti-coercion/fishing tool.
• Menu

  vbarrielle
  The 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.
• yoavsha1
  Why base this on time? Using a simple HOTP which uses a rolling index for the "time value" seems like a much better choice for humans
• Menu

  eisbaw
  or we could use asymmetric biometric fingerprints. Turns out features can be extracted into public and private sets, and both are required for a match. I hold a patent on it btw
• Menu

  MattPalmer1086
  What is the purpose of the 6th digit?It doesnt add any security, as it is trivially computable from the other digits already computed.It appears to be a checksum, but I can't see why one would be needed.
• wolvoleo
  Interesting idea but I don't think my users will grok this :)The worst thing about it is that people will go like "uuuh naaaah" and will just grab a random app off the play store and put their code in it. Now you are leaking secrets to whatever random app they use.
• Menu

  onion2k
  I don't think people plan what time to log into things.
• Menu

  deafpolygon
  I see 2FA is often misunderstood by people. The basic premise with 2FA is that you combine “something you know” with “something you have”.You are already part of the 2FA — you’re the first factor: “something you know”.The second factor: “something you have” — often a personal device, or an object. This is ideally something no one else can be in possession of at the same time as you are.
• Menu

  swiftcoder
  Isn't this just manually hashing a password with a timed-salt? I don't see how this relates to TOTP
• cuckovic
  Really nice idea