Hello Alian ,
Could you please check this out https://www.oracle.com/fr/a/ocom/docs/aso_12c_faq.pdf
TDE has a two-tier key architecture, with data encryption keys that are wrapped by a single database master key .......
This does not answer to the question.
I have one database, one tablespace per customer. A customer has asked to choose an encryption key for its tablespace that has to be different than the one for used to encrypt the other tablespaces (other customer's data). Question: feasable? And if yes, how? (example please).
From what I found, I can only set a master key at database level (and so the only possibility I found is to have several databases or cdb's).