If you are asking for specific knowledge you will have to go thru vast amount of developer, and when you find those, they will lack other knowledge. But what differentiate a good developer to a bad is : what question to ask to get the requirement, and how to proceed to research for lack of information. So not knowing about a specific encryption is not bad, if the developer ask the correct requirement question and demonstrate a willingness to search for correct source depending on such requirement. the specific question does not matter, it could as well be about a robotic software to remove feather from dead chicken in an assembly line. In your specific case i would ask why you chose this specific encryption, if you have a specific vendor or open source in mind, what would be the timing requirement (can it run slow) what would be the memory footprint requirement , how often it is used, what would be the liability for vulnerabilities, how are the key managed, are there legal requirement on the key management etc...etc...