6 ms·

"They should also enable two-step verification for their iCloud accounts. This will protect iCloud accounts from attackers even if the account password is compr

by dewiz 12y ago

"They should also enable two-step verification for their iCloud accounts. This will protect iCloud accounts from attackers even if the account password is compromised." I wonder if 2FA is really that safe in a country like that, they have all the means to intercept the second channel, it just requires knowledge about the account owner or some not to complex synchronization to detect auth codes sent via text messages.

dwild 12y ago
That's why I don't like 2FA with SMS. How can you trust a password that's send in clear through multiple carrier. A good 2FA doesn't require anything else than the local time to generate the current password.
- nkozyra 12y ago
  2FA doesn't normally send a password though, does it? Isn't it typically a one-time key? The risk here is someone could intercept and set/reset that password, but the end user would immediately know that as they would be unable to set a password or login.
  - worklogin 12y ago
    With app- or token-based 2FA, there is no token sent across the wire until the user submits an auth request. With SMS-based 2FA, the token is sent via insecure channels to the user BEFORE auth, which is an opportunity for state actors and telecom to intercept it before use.
    - nkozyra 12y ago
      Right, I'm pretty sure we're taking about SMS-based (or perhaps email-based). Even in cases where that token is intercepted, it's a one-time use token, so you know if it's been intercepted.
      - acqq 12y ago
        If somebody can MTM both SMS and your internet connection, you wouldn't know a thing. That one use would be done by the MTM and not you and thanks to the MTM everything would appear normal to you. (MTM is not only the "man in the middle" but also "the machine in the middle" -- a computer which would react in real time.)
        nkozyra 12y ago
        Yes, you would know, because the token exists to establish a password and an active connection. If someone MTM the 2nd part of a 2FA, you won't be able to log into your account. MTM your internet connection means whatever the service is you have to replicate exactly, which is not feasible at any scale.
        acqq 12y ago
        MTM is the point where your active connection ends. It uses the token to connect with the server (which it knows since it MTMs the SMS too), you comunicate with it, seeing the copy of what MTM receives. You don't see anything strange. It's not that hard to implement.
        nkozyra 12y ago
        Again, this is confusing the MTM attack we're (and most people are) talking about in general with the 2FA mechanism we're specifically talking about here. They're two entirely different vectors. If you wanted to hijack a token as part of a 2FA, that serves the purposes of initializing an account. In this case, the second MTM (intercepting communications) will not work, because the user will be unable to log in (as you initialized their account and therefor had to set a password). Further, in the traditional MTM attack, there's no need to steal that 2FA token in the first place - not only because it prevents an active, working account, but because you can already get the information you want through data interception.
        acqq 12y ago
- smtddr 12y ago
  >>That's why I don't like 2FA with SMS. How can you trust a password that's send in clear through multiple carrier. Hmm, maybe websites should allow people to select an "encryption" format for the SMS. Something not too complicated, like a ROT13'ish type of thing: "We'll txt you the code, but every 3 char should be ignored... or every 4th number should be multipled by 3"
  - josho 12y ago
    I suspect that anything that a user could be reasonably expected to perform wouldn't provide enough additional security to make the additional effort worthwhile.
  - DasIch 12y ago
    The general assumption in cryptography that the algorithm used for encryption is known. Even if you relax that restriction and assume you know which algorithms a user can choose but not which one she chose, you could still just try all of them, if they are "not too complicated".
    - esrauch 12y ago
      If 3 login attempts invalidate the OTP then you only need a manageable number of different "known modifications" to tell the user through the secure channel to keep this safe. If they can arbitrary brute force you OTP anyway then the OTP isn't really going to be all that useful at 10k possibilities. That said, hardly any user would be willing to take on such complexity without very strong reason.
- deleted 12y ago
  [deleted]
jacobsenscott 12y ago
A good MITM attack intercepts your second factor when you enter it, just as it intercepts your password. Then the attacker just signs in before your second factor expires.
Sami_Lehtinen 12y ago
What's the problem with 2FA with SMS? I'm using it and it's good. They send signed SMS with nonce, I'll verify the signature with their public key, and sign it with my private key, then send the signed nonce back. Then the web interface tells me that now I have successfully signed their request nonce XXX, and they'll be forwarding my login token to authority X. So it's not so easy to tamper with properly made mobile SMS 2FA. My phone never receives the actual login token, nor the service X get's it unless I'll also verify the login request in browser. Of course before all this happens, I also would have given preliminary login information like username and password.

by dewiz 12y ago

dwild 12y ago

That's why I don't like 2FA with SMS. How can you trust a password that's send in clear through multiple carrier. A good 2FA doesn't require anything else than the local time to generate the current password.

nkozyra 12y ago
2FA doesn't normally send a password though, does it? Isn't it typically a one-time key? The risk here is someone could intercept and set/reset that password, but the end user would immediately know that as they would be unable to set a password or login.
- worklogin 12y ago
  With app- or token-based 2FA, there is no token sent across the wire until the user submits an auth request. With SMS-based 2FA, the token is sent via insecure channels to the user BEFORE auth, which is an opportunity for state actors and telecom to intercept it before use.
  - nkozyra 12y ago
    Right, I'm pretty sure we're taking about SMS-based (or perhaps email-based). Even in cases where that token is intercepted, it's a one-time use token, so you know if it's been intercepted.
    - acqq 12y ago
      If somebody can MTM both SMS and your internet connection, you wouldn't know a thing. That one use would be done by the MTM and not you and thanks to the MTM everything would appear normal to you. (MTM is not only the "man in the middle" but also "the machine in the middle" -- a computer which would react in real time.)
      - nkozyra 12y ago
        Yes, you would know, because the token exists to establish a password and an active connection. If someone MTM the 2nd part of a 2FA, you won't be able to log into your account. MTM your internet connection means whatever the service is you have to replicate exactly, which is not feasible at any scale.
        acqq 12y ago
        MTM is the point where your active connection ends. It uses the token to connect with the server (which it knows since it MTMs the SMS too), you comunicate with it, seeing the copy of what MTM receives. You don't see anything strange. It's not that hard to implement.
        nkozyra 12y ago
        Again, this is confusing the MTM attack we're (and most people are) talking about in general with the 2FA mechanism we're specifically talking about here. They're two entirely different vectors. If you wanted to hijack a token as part of a 2FA, that serves the purposes of initializing an account. In this case, the second MTM (intercepting communications) will not work, because the user will be unable to log in (as you initialized their account and therefor had to set a password). Further, in the traditional MTM attack, there's no need to steal that 2FA token in the first place - not only because it prevents an active, working account, but because you can already get the information you want through data interception.
        acqq 12y ago
smtddr 12y ago
>>That's why I don't like 2FA with SMS. How can you trust a password that's send in clear through multiple carrier. Hmm, maybe websites should allow people to select an "encryption" format for the SMS. Something not too complicated, like a ROT13'ish type of thing: "We'll txt you the code, but every 3 char should be ignored... or every 4th number should be multipled by 3"
- josho 12y ago
  I suspect that anything that a user could be reasonably expected to perform wouldn't provide enough additional security to make the additional effort worthwhile.
- DasIch 12y ago
  The general assumption in cryptography that the algorithm used for encryption is known. Even if you relax that restriction and assume you know which algorithms a user can choose but not which one she chose, you could still just try all of them, if they are "not too complicated".
  - esrauch 12y ago
    If 3 login attempts invalidate the OTP then you only need a manageable number of different "known modifications" to tell the user through the secure channel to keep this safe. If they can arbitrary brute force you OTP anyway then the OTP isn't really going to be all that useful at 10k possibilities. That said, hardly any user would be willing to take on such complexity without very strong reason.
deleted 12y ago
[deleted]

jacobsenscott 12y ago

A good MITM attack intercepts your second factor when you enter it, just as it intercepts your password. Then the attacker just signs in before your second factor expires.

Sami_Lehtinen 12y ago

What's the problem with 2FA with SMS? I'm using it and it's good. They send signed SMS with nonce, I'll verify the signature with their public key, and sign it with my private key, then send the signed nonce back. Then the web interface tells me that now I have successfully signed their request nonce XXX, and they'll be forwarding my login token to authority X. So it's not so easy to tamper with properly made mobile SMS 2FA. My phone never receives the actual login token, nor the service X get's it unless I'll also verify the login request in browser. Of course before all this happens, I also would have given preliminary login information like username and password.