Our goal in this study is to understand to what extent Open-TEE addresses the difficulties encountered by developers of Trusted Applications (TAs) for Trusted Execution Environments (TEEs).

This user study consists of three steps. First we would like you to fill out a pre-study questionnaire, the purpose of which is to collect background information on the participants. After the pre-study questionnaire there will be a little exercise. You will be asked to use Open-TEE to complete the exercise, and afterwards fill out a post-study questionnaire, the purpose of which is to collect information about your experience in using Open-TEE in this particular exercise.

The results of this study will be used to further Open-TEE development and therefore we would appreciate your feedback.


This user study is mainly aimed towards people who are acquainted with TEEs and have developed TAs. The user study itself does not need any special beforehand skills or knowledge. We have composed a tutorial and user guide for Open-TEE you can refer to throughout the study. However, anyone interested in this subject is still welcome to participate even if he/she does not have TA development experience.


Before beginning the actual user-study, please make sure that you have Open-TEE deployed. For instructions on how to build and install Open-TEE please see the tutorial page.


In case of questions about the user study, please see the contacts page. In case of technical problems, also feel free to contact us.


Pre study questionnaire

Post study questionnaire

User study: step 1

In the first phase of the user study, please take some time to fill out the pre-study questionnaire. Fill out the questionnaire as best as you can following the instructions in the beginning of the form. Please complete the steps in order and do not skip any of the steps.

User study: step 2

You will be using Open-TEE for debugging a Trusted Application. The debugging is needed because we have purposely injected some bugs into this user study TA, and your task is to fix it. You will be working with a “virtual wallet” type application. This application has been implemented only for use in this user study, and should not be used as a reference in implementing TAs for production use.


In this exercise, you will be focusing only on the TA application. Bugs have been introduced only into this application. Open-TEE and corresponding Client Application do not need attention, in this exercise, and therefor you can assume that they are implemented correctly. The bugs introduced to the TA are not logical in nature and all algorithms work as they are supposed to and are returning correct values.

First test run with bug

Now we assume that you have set up the Open-TEE environment. To execute the first test run, follow the steps below:

  1. If not running already, launch Open-TEE as per the instructions on the tutorial page.

  2. Navigate into the Open-TEE directory. The user study source code is in two parts, the Client Application (CA) and the Trusted Application (TA) located at CAs/usr_study_ca/ and TAs/usr_study_ta/ respectively.

    The test binary is called “usr_study_ca” and located under the gcc-debug/ directory. It is important that you have not modified this binary yet.

  3. Run user study binary. You will see the following print out onto the console:

START: usr study app
Initializing: Ok
Making transactions: failed: TEE_ERROR_TARGET_DEAD
Run summary: FAILED
END: usr study app

If you see this print out, then all is well. Now you can proceed debug the TA.

Debugging the TA

As mentioned previously, all the bugs introduced are located in TA code. The TA source file is located at TAs/usr_study_ta/

The TA is called “usr_study_ta”. For tracking down the bugs, you can use your own favorite method. For example, you could use GDB.

Once you have pinpointed the location of the bugs, fix them in the TA source file. After saving you changes, recompile the TA.

Re-run debugged TA

Once you have fixed the bugs it is time to verify if all the bugs have been found and fixed by following the steps below:

  1. Open-TEE should now be running. Do not launch it the second time.
  2. Execute the corresponding Client Application.
  3. You will be getting a print out on your console. In case you have found and fixed all the bugs, you will see the following print out:
START: usr study app
Initializing: Ok
Making transactions: Ok
Querying account: Ok
Getting random transactions: Ok
Executing TA self checking: Ok
Resetting account: Ok
Testing unknown cmd: Ok
Executing TA self checking: Ok
Run summary: PASS
END: usr study app

Verify your result by comparing your print out to the print out above. Note the line at the end of the print out indicating if the run passed or failed. If the run fails, go back to step 2.

In case of success, this part is done and you can proceed to step 3. If you have no alternative use for Open-TEE, you can remove Open-TEE.

User study: step 3

Please fill out the post study questionnaire. Instructions can be once again found in the questionnaire itself. Step 3 should be completed based on your experience with OpenTEE in step 2. If you are unable to complete step 2 successfully, please still fill out the questionnaire.

User study: step 4

Do not forget to return the two questionnaires!


After completing the steps mentioned above, your part has been successfully completed. We thank you for taking the time to participate in the user study. If during the user study or after finishing it, you developed any questions about the user study or Open-TEE, please do not hesitate to contact us. Any additional feedback would also be welcome.