In order to facilitate a meaningful qualitative and quantitative, discussion regarding the scientific and technical challenges follows a 3- dimentional diagram, shown in Figure 2. The diagram depicts the two initial methods used to investigate and realize the remote entrusting principle. Two of the three dimensions describe a SW-based method (code tamper resistance and code replacement) and the third dimension describes a HW/SW-based method (tamper resistance (tr) using combined hardware (e.g., smart cards) and software).

Figure 1: Quality of remote entrusting

Next is a brief discussion of selected scientific and technical challenges as projected by Figure 2.

SW-based - Tamper-resistance quality

• Combining two programs: original together with tag generator into "secure SW module".
• Protecting the secure SW so it is hard to separate by increased program cohesiveness.
• Hiding the semantic of the secure SW module by means of obfuscation, for example.
• Measuring the complexity of reverse engineering of the secure SW module.

SW-based - Dynamic replacement

• Replacement of SW component in run-time is different from the current operating system (OS) paradigm.
• Replacement of SW component while resisting tampering by the OS is a new challenge.
• Analyzing trade-off between dynamic replacement frequency and tamper-resistance quality.

HW/SW-based - Tamper-resistance and encryption quality

• Tamper-resistant co-design of applications with software and hardware components.
• Analyzing trade-off between hardware and software.
• The security of communication between the secure SW module and the HW component.