Bitcoin/Litecoin expert developer

We requiere a bitcoin expert developer to add some modifications on the original release. In a fork of the original bitcoin we need: Confirming transaction process and block creation only can be made by an autorized pools. In other words, search a system that by a "certificate", pools can sign new blocks to the network. A block not signed correctly will be rejected. For done the work you will explain your modifications made in bitcoin source, and modify the php-mpos to support this functions. A VPS (debian) to test php-mpos will be provided. The wallet source code will work in unix, mac and windows.