S/KEY (One-Time-Password) generator

[reezer]

Hi,

I think it would be very nice if one could generate OTPs with Rockbox. They can protect against various attacks, especially when you use untrusted computers. S/KEY works on Linux and BSD operating systems.

Wikipedia is a nice starting point providing links to implementations and RFCs:
https://secure.wikimedia.org/wikipedia/en/wiki/S/KEY

[torne]

This is a good idea in principle, but entering text on the players is something of a pain; so typing your passphrase would be very annoying, no? RFC2289 mandates a minimum of ten characters

[reezer]

You don't need to enter it for every password.

There is also an alternative. Let it generate a random password which gets printed and then tell the system you want to login to it will be used. That way you don't need to enter anything.

[torne]

You don't need to enter it for every password.

There is also an alternative. Let it generate a random password which gets printed and then tell the system you want to login to it will be used. That way you don't need to enter anything.

To use an OTP system securely, the calculator device/program can't store the password for you, otherwise the device, if stolen, can be used to log in as you. There needs to be a component that the user memorises as well: this is the password. The OTP calculator doesn't need to store any data at all, the password plus the challenge from the server is sufficient to calculate the response (though it can, safely, store the challenge's data part and remember the last counter value, assuming it decrements by one each time - this saves time entering data as this information is not secret anyway, the host tells it to anyone who tries to log in with your username).

[pabouk]

To use an OTP system securely, the calculator device/program can't store the password for you, otherwise the device, if stolen, can be used to log in as you.

Yes, by omitting the password you get weak authentication (single factor) instead of strong one (two factor). In reality you can find many commercial OTP tokens which are not directly protected by PIN/password. For example see:
* SafeNet eToken PASS
* VASCO DIGIPASS GO series
* RSA SecurID
All of the above widely used products allows sending the PIN/password together with the generated OTP so the token (rockboxed player in our case) does not need to allow entering PIN/password. Of course this solution is less secure but it is being used widely.

I agree that entering alphanumeric password or OTP challenge into a player is really awkward so it is better to:
- use response only OTP
- use above mentioned solution with sending password together with OTP or
- use a special password like sequence of directions (I think all the players have direction keys) instead of alphanumeric characters