Objective to c# dll

I'm looking for a developer who has extensive experience developing C# DLLs for a new application written in Objective-C. The purpose of the DLL is for development and the DLL should provide functionalities such as data encryption, file manipulation, and network communication. The developer should be familiar with the tools and technologies used for developing DLLs and will be expected to work efficiently towards producing the best possible product. If the project is successful, there is potential for further work.