Oracle change TDE Tablespace Encryption From AES128 To AES256

Check the encryption algorithm for the tablespace created.

SQL> select name, encryptionalg encryptedts from v$encrypted_tablespaces e, v$tablespace v where e.ts# = v.ts#;

NAME			       ENCRYPT
------------------------------ -------
TEST_ENC128		       AES128

Check the file name and the file existing.

SQL> select file_name from dba_data_files where tablespace_name like 'TEST_ENC128';

FILE_NAME
------------------------------------------------------------
/u01/app/oradata/ORCL/datafile/test01.dbf
/u01/app/oradata/ORCL/datafile/test02.dbf

Change the Encryption Algorithm to AES256 for the esisting tablespace using REKEY command.

SQL> alter tablespace test_enc128 encryption using 'AES256' rekey;

Tablespace altered.

Check the encryption algorithm of the tablespace.

SQL> select name, encryptionalg encryptedts from v$encrypted_tablespaces e, v$tablespace v where e.ts# = v.ts#;

NAME			       ENCRYPT
------------------------------ -------
TEST_ENC128		       AES256

You must use the FILE_NAME_CONVERT clause for non-Oracle managed files.

(In an OMF - Oracle-managed files configuration, new data files are created automatically.)

--For non-Oracle Manager Files
SQL> alter tablespace test_enc128 encryption using 'AES256' rekey file_name_convert = ('test01.dbf','test01_aes256.dbf');

--For Oracle Manager Files
SQL> alter tablespace test_enc128 encryption online using 'AES256' rekey;

Documents:

How to change TDE Tablespace Encryption From AES128 To AES256 in 12.2 (Doc ID 2456250.1)