CLOSE MASTER KEY (Transact-SQL)
Closes the master key of the current database.
CLOSE MASTER KEY
Takes no arguments.
This statement reverses the operation performed by OPEN MASTER KEY. CLOSE MASTER KEY only succeeds when the database master key was opened in the current session by using the OPEN MASTER KEY statement.
No permissions are required.
USE AdventureWorks2012; CLOSE MASTER KEY; GO