All I can say is never do trade in the exchange asking your private key for you to be able to use their platform. That's the dangerous things which you going to do if you do what they are requiring you on the etherdelta. No wonder why it has an issues before a months ago. So. if you want to be safe your coins use other exchange not this one which is Etherdelta. Because, even the no. 1 exchange platform in this industry they are not asking private key to their client users, just all you need to do is to signup first to their exchange and apply for kyc.