Can indexed columns be encrypted?
TDE tablespace encryption supports all indexes transparently. For TDE column encryption, the index needs to be a normal B-tree index, used for equality searches. In case of a composite, function-based index, the encrypted column cannot be the one that was used for the function. When encrypting a column with an existing index, it is recommended to first extract the index definition with dbms_metadata.get_ddl, then drop the index, encrypt the column with the ‘no salt’ option, and re-build the index.
