db19c inplace encryption

Once a TDE has been implemented for a database, to encrypt existing tablespace:

ALTER SYSTEM SET "_tablespace_encryption_default_algorithm" = 'AES256' SCOPE=BOTH SID='*';

Now encrypt all tablespaces, for example:

ALTER TABLESPACE SYSAUX             ENCRYPTION ONLINE ENCRYPT;
ALTER TABLESPACE USERS              ENCRYPTION ONLINE ENCRYPT;
ALTER TABLESPACE SYSTEM             ENCRYPTION ONLINE ENCRYPT;
ALTER TABLESPACE UNDOTBS1           ENCRYPTION ONLINE ENCRYPT;
ALTER TABLESPACE UNDOTBS2           ENCRYPTION ONLINE ENCRYPT;
ALTER TABLESPACE MGMT_AD4J_TS       ENCRYPTION ONLINE ENCRYPT;
ALTER TABLESPACE MGMT_ECM_DEPOT_TS  ENCRYPTION ONLINE ENCRYPT;
ALTER TABLESPACE MGMT_TABLESPACE    ENCRYPTION ONLINE ENCRYPT;
ALTER TABLESPACE UNDO_2             ENCRYPTION ONLINE ENCRYPT;

Do the same for temporary, creating new tablespaces (the former one will need to be deleted)

CREATE TEMPORARY TABLESPACE tempo TEMPFILE '+DATA' SIZE 200M ENCRYPTION ENCRYPT;
ALTER DATABASE DEFAULT TEMPORARY TABLESPACE tempo;
DROP TABLESPACE temp;

Note:
1) Make sure the standby wallet is current
2) The operation will create new datafiles, and zero out the original ones.
3) Although the new encryption will be carried over to the standby, the temporary tablespace will not. Add the necessary tempfile on the standby (ALTER TABLESPACE temp ADD TEMPFILE SIZE 200M;)