CLOSE SYMMETRIC KEY (Transact-SQL)
Closes a symmetric key, or closes all symmetric keys open in the current session.
Open symmetric keys are bound to the session not to the security context. An open key will continue to be available until it is either explicitly closed or the session is terminated. CLOSE ALL SYMMETRIC KEYS will close any database master key that was opened in the current session by using the OPEN MASTER KEY statement. Information about open keys is visible in the sys.openkeys (Transact-SQL) catalog view.
A. Closing a symmetric key
The following example closes the symmetric key
CLOSE SYMMETRIC KEY ShippingSymKey04; GO
B. Closing all symmetric keys
The following example closes all symmetric keys that are open in the current session, and also the explicitly opened database master key.
CLOSE ALL SYMMETRIC KEYS; GO