Data Security in MS SQL Server How do I store the sensitive information on SQL server?. We have policy guidelines, DBA and Development engineers are not allowed to view the data as plain text.

I am aware of the encryption technologies and data masking technologies but the problems is, except the person who is directly responsible for the data, no one else can access the data as per the policy. 

When developers need to perform some calculation on sensitive information, how is it possible to do that, without decrypting? while still allowing SysAdmin users to view the encryption key details? I am sure, I am not the first one to implement this system. How do I design this solution? Thank you!

Edit 1:

Is it possible to create a reference column based on the original column and give it to developer for calculations? In that case, how to avoid direct logics or how to avoid people reverse engineer the logic and how is it possible to keep the encryption / hashing logic away from DBA.

I am open to any other suggestion or workarounds. Thank you!
One alternative is to encrypt and decrypt in the app, and SQL server will of course have no knowledge that this data was born as anything else. Or, in SQL Server 2016, use Always Encrypted which means that the database API (ODBC, ADO.NET, JDBC...) does the job for you. Regardless of which solution, make sure that the DBA don't have access to the key. And, since the whole point is that the SQL Server never sees the clear-text data, you cannot manipulate using pure T-SQL. (In SQL Server 2019 will will have secure enclaves allowing for the database engine to decrypt the data to allow for things such as rotation of keys, LIKE, BETWEEN etc, but that isn't released yet.)