Before Oracle Database 18c, the only way to encrypt data (all types of data) was using the parameters ENCRYPTION_PASSWORD or ENCRYPTION_PWD_PROMPT. The data is exported in clear text in an export operation (expdp) even if Transparent Data Encryption (TDE) was used to store the data in the database, but the parameters ENCRYPTION_PASSWORD and ENCRYPTION_PWD_PROMPT were not used.
This is a companion discussion topic for the original entry at https://blog.toadworld.com/encrypt-database-link-passwords-with-data-pump-in-oracle-18c