A secure data processing apparatus and method are disclosed. The secure data processing apparatus is operable to securely process user data provided by a user and includes a trusted domain having a trusted bus; a trusted domain controller coupling the trusted bus with an untrusted bus of an untrusted domain, the trusted domain controller being operable to ensure that encrypted incoming user data received over the untrusted bus is decrypted and provided over the trusted bus as the incoming user data and to ensure that outgoing user data is encrypted and provided over the untrusted bus as encrypted outgoing data. The trusted domain controller that only encrypted data is provided in the untrusted domain reducing the chance of the data being compromised. The trusted domain controller ensures that access to the unencrypted data within the trusted domain can be avoided. Confidentiality of the data can be assured without performance shortfalls.