When restoring a database you might get the below error.
System.Data.SqlClient.SQLError: Cannot find server certificate with thumbprint
This is because the database was encrypted with Transparent Data Encryption (TDE) and you will not be able to restore it until you get the Certificate, the Private key and the password from the supplier of the database.
After you collect the required items above, open a new SQL query as the server admin on the database master.
First we need to create the master cerificate on the server by using
CREATE MASTER KEY ENCRYPTION BY PASSWORD = '<MyComplexPassword>'
Now that the master certificate has been installed you will need to install the certificate provided by the owner of the database
CREATE CERTIFICATE MyServerCert
FROM FILE = 'C:\TDECert\Cert.cer'
WITH PRIVATE KEY (FILE = 'C:\TDECert\key.pvk',
DECRYPTION BY PASSWORD = '<PasswordProvidedByTheSupplier>');
Once this is done and executed you will be allowed to restore the database.