Changing SQL Certificates and/or Symmetric Keys

Question

Re: Changing SQL Certificates and/or Symmetric Keys
We need to encrypt some sensitive data and are looking at SQL Column Level encryption, using symetric keys.
For example, we are following this example
http://www.mssqltips.com/sqlservertip/2431/sql-server-column-level-encryption-example-using-symmetric-keys/
We are told that we might be required to change certificates and/or keys on a schedule, say every 1 year. How how do you change certificates and/or keys and what is the ramification for the data that is encrypted using them - say EncryptedColumn1? 
-- Create self signed certificate
USE encrypt_test;
GO
CREATE CERTIFICATE Certificate1
WITH SUBJECT = 'Protect Data';
GO
-- Create symmetric Key
USE encrypt_test;
GO
CREATE SYMMETRIC KEY SymmetricKey1
WITH ALGORITHM = AES_128
ENCRYPTION BY CERTIFICATE Certificate1;
GO
-- Populating encrypted data into new column
USE encrypt_test;
GO
-- Opens the symmetric key for use
OPEN SYMMETRIC KEY SymmetricKey1
DECRYPTION BY CERTIFICATE Certificate1;
GO
UPDATE Customer_data
SET Credit_card_number_encrypt = EncryptByKey (Key_GUID('SymmetricKey1'),Credit_card_number)
FROM dbo.Customer_data;
GO
-- Closes the symmetric key
CLOSE SYMMETRIC KEY SymmetricKey1;
GO

Answer 1

I think you are saying that to recycle the certificate (Certificate1) in my example to use anALTER SYMMETRIC KEY DROP ENCRYPTION  then ALTER SYMMETRIC KEY ADD ENCRYPTION and my column data will still be encrypted with the same key but built upon a different
certificate.
Yup.
what happens when i need to recycle the key?
Then it gets messy. You will need to descrypt and reencrypt with the new key.
I'm not well versed in the requirements for which keys to recycle, but I note that in SQL Server, certificates has an expiration date. Symmetric keys have not. Also, certificates can be imported and be signed by a trusted provider. Symmetric keys are
some random bits created in SQL Server. (With the exception of keys från EKM devices, which is a rare thing.)
Erland Sommarskog, SQL Server MVP, [email protected]