I must be missing something. I'm sure someone can put me straight. This link says that you need to restore both the DEK and the certificate http://msdn.microsoft.com/en-us/library/bb934049.aspx. I chose the first answer because of this.
When enabling TDE, you should immediately back up the certificate and the private key associated with the certificate. If the certificate ever becomes unavailable or if you must restore or attach the database on another server, you must have backups of both the certificate and the private key or you will not be able to open the database. The encrypting certificate or asymmetric should be retained even if TDE is no longer enabled on the database. Even though the database is not encrypted, the database encryption key may be retained in the database and may need to be accessed for some operations. A certificate that has exceeded its expiration date can still be used to encrypt and decrypt data with TDE.
Thanks,
Tom