On the destination server after migration. OPEN the database master key using the same password as on the source server.
NB : The OPEN command works for the same session only, the decryption capability does not work for other sessions or when the current session closes. then ALTER the database master key to associate it with the current instance’s service master key
OPEN MASTER KEY DECRYPTION BY PASSWORD = ‘yourMasterKey’
ALTER MASTER KEY ADD ENCRYPTION BY SERVICE MASTER KEY
follow this link https://www.simple-talk.com/sql/database-administration/encrypting-your-sql-server-2012-alwayson-availability-databases/ to read about AAG and TDE
SQL 2000/2005/2008/2012 DBA - MCTS/MCITP