How is TDE different from the encryption toolkit Oracle already provides?
Oracle introduced an encryption package (‘dbms_obfuscation_toolkit’) with Oracle8i. In Oracle 10g Release 1, the new ‘dbms_crypto’ package was introduced. These APIs can be used to manually encrypt data within the database. However, the application must manage the encryption keys and perform required encryption and decryption operations by calling the API. As opposed to dbms_obfuscation_toolkit and dbms_crypto, both TDE column encryption (from 10gR2) and TDE tablespace encryption (from 11gR1) don’t require changes to the application, are transparent to the end users, and provide automated, built-in key management.