Viewpad 10s - Stuck On 'Starting Fastboot USB Download Protocol'

I seemed to have lost recovery mode & completely messed up the tablet. AlI I can get now is fastbboot mode and message ''Starting Fastboot USB Download Protocol'.

How can I flash a rom now please?

adb raw protocol AUTH

Hello,

as the title says, i have some trouble with the A_AUTH packet. I currently write my own implementation of the adb protocol for my AndroidCtrl.dll everything works so far as expected, only the token signing left...

QUESTION:
Can someone kick me in the right direction, how i can successfully sign the A_AUTH token?

My tries [C# .Net 4 Client]

Code:

---

//Class internal var
RSACryptoServiceProvider _rsaSP = new RSACryptoServiceProvider(2048);

// (my own loader) Load the xml saved RSA-Key
RSALoad()

// generate the signed hash
// (don't work)
byte[] shash = _rsaSP.SignData("20 byte token from A_AUTH", new SHA1CryptoServiceProvider()));

// generate the signed hash
// (don't work)
byte[] shash = _rsaSP.SignData("20 byte token from A_AUTH", new SHA256CryptoServiceProvider()));

---

I also tried it with "_rsaSP.SignHash()" but no luck... Seems .Net is not capable to sign a adb token... If i send my public key, on the device the adb dialog pops up and ask me to grand access. So the device have the public key. But it sends all the time a new token after i send my signed token...

THX in advance
Sebastian