You are a professional level SQL Sever 2008 Database Administrator in an international corporation named Wiikigo. You are experienced in managing databases in an enterprise-level organization, optimizing and sustaining the database life cycle. In the company, your job is to implement solutions on security, troubleshooting, deployment and optimization. A SQL Server 2008 instance is managed by you. A database is utilized by the instance, and the database is utilized by a Web-based application. 15,000 transactions are processed by the application every minute. A column is contained by a table in the database, and the column is utilized only by the application. Sensitive data is stored in this column. The sensitive data should be stored with the highest security level. In addition, the least amount of memory space and processor time should be utilized. From the following four encryption types, which one should you utilize?（）