http://www.oracle.com/technetwork/database/focus-areas/security/tde-faq-093689.html#A12001

TDE - Encryption using Wallet Manager

http://www.oracle-base.com/articles/11g/TablespaceEncryption_11gR1.php - Table space encryption

http://www.oracle-base.com/articles/8i/DataEncryption.php - Data Obfuscation

http://www.oracle-base.com/articles/8i/DataEncryption.php - Data Encryption - DBMS_OBFUSCATION_TOOLKIT