I'm searching for a way of authentication like that from Blizzard (Authenticator). It creates an off-line OTP. I know that larger companies use it as "tokens" however, I'm still unable to find a proper library.
So, what I want; A project that is able to create OTPs on the client side without having the client to connect to the internet and yet be able to generate the exact same on the servers-side.
I think you can take a look at this library: https://code.google.com/p/otpnet/
It is a C# port of a popular TOTP/HOTP for PHP. There seems to be a few outstanding issues in the library which have not yet been fixed by the developers but you can easily patch it on your side with recommendations that have already been submitted.