Digital signature in network protocol

Originally posted by ArC

In order to create digital signatures which are accepted by the server you will have to know the private key which is used in order to create the signature. If you know it, you will be able to create "fake" signatures which are accepted by the server.

However, if the guys implemented the algo correctly, there's no way to use a "generic" signature or something smilar.

Then how those legitimate clients can connect BK server? If people have no access to BK server there will be no way to intercept, but the product BK selling includes those servers.