SKIMS Trust Evaluator

Welcome to the SKIMS Trust Evaluator. On this site you will find information about the survey application SKIMS Trust Evaluator that we developed to investigate sociological inspired trust establishment. This empirical study is part of the SKIMS research project at Freie Universität Berlin, Computer Systems & Telematics Group. The corresponding app is available for Android-based smartphones. The project is sponsored by the German Federal Ministry of Education and Research.

We hope you find all information you need to understand the purpose and mode of operation of our app, otherwise please contact us. We would be very delighted if you support our research by installing the application and taking two minutes time to execute it and answer a few questions.

Quick overview
  • We want to study the following question: "On which base do you trust your social contacts?"
  • The Trust Evaluator analyzes your call and message logs for research purposes in a privacy friendly way.
  • It then displays some of the most and least frequently contacted people in your contact list.
  • You rate these contacts according to your grade of closeness and trust.
  • After you are done rating some of your contacts an email will be prepared which contains in a text file attachment anonymized data about the calls and messages you sent out. For details see the listing below.
  • Please do not forget to add your MTurk ID in the final email sent from your phone.
  • To participate, please download here. For experts, it includes also the source code to verify the program.

Note that all data is completely anonymized (no names, numbers, dates, etc.). You can decide by yourself whether or not you are sending out the email. You can be sure that no data is transmitted without your acknowledgment: The SKIMS Trust Evaluator does not request the permission for Internet access. Any information intended for transmission will be shown beforehand via your standard email client and must be confirmed by you. Note also that any data that is assembled by the SKIMS Trust Evaluator can be gathered by any other application on your Android mobile.

In the following sections, we describe in detail what we are looking for and tell you why and how we hope to accomplish this.

Why we created this app

In our research project SKIMS we explore enhanced security mechanisms for smartphones. In particular we are trying to establish trust between two mobile phones by using the social network of the phones' users: If two people trust each other, their phones may trust each other to some extent, as well. The challenge is to find this "social trust" and so we are looking for ways to define trust through data available on the phone. A promising direction is the analysis of mutual contacts between two users (you can read about it in [1]). If two people share many mutual contacts they might trust each other more than people sharing only a few contacts. In order to further classify the contacts (e.g., in classes like close friends or loose acquaintance) we look at the amount of interaction a phone user has with a contact.

And this is where the SKIMS Trust Evaluator comes into play. We want to find out how exactly interaction between two parties correlates with trust between these persons. Does a high call frequency always indicate a good friend or could it not also point to an ongoing conflict? Thus, we ask you to give a rating to some of your contacts in terms of closeness and trust. We will also note some statistics about your call and message interactions to automatically derive a trust measurement.

How it works

After downloading and installing the app, the welcome screen will be shown. In the meantime the SKIMS Trust Evaluator analyzes your call and message logs: the calls and messages are grouped by your communication partner, i.e., the app maps each contact to the interactions he or she has had with you. Based on this information the Trust Evaluator chooses some contacts you are asked to rate. This will include the contacts you had the most and the least interaction with, as well as a some contacts chosen randomly. As soon as the Start button appears the analysis is finished and you can start rating the pre-selected contacts. We are asking your level of agreement to the following three questions:

     I feel close to this person

     I would trust this person with sensitive information

     I trust that this person wants the best for me

If the contact that is displayed is not a real person but a business number (e.g., a service hotline, your mailbox, or a local store) press the button This is not a person in the upper right corner of the screen. You will be shown a new contact instead.

After the rating you will be shown a Send email button. Pressing this will open your phone's email client (or ask you which one you want to use, in case there is more than one) and present you an email containing the first lines of the results of your rating. The complete results are attached as a text file to the email. The data is encoded in the YAML format, the meaning of every field is explained below. You can have a look at the data to assure yourself that we are not sending out sensitive data. After sending out the email to us, your Android phone will go back to your home screen. You can now uninstall the SKIMS Trust Evaluator.

Thank you for supporting our research!


Please download the apk file here. Downloading the file with your Android phone is probably the easiest way. It requires at least Android version 2.2 (API 8) to run.

If you are interested in the source code of our application (e.g., to verify the program), you can download it here.

The data sent in the email

In the following we will be describing the YAML data that is send out after the trust evaluation by the user. All information can be double checked by the user before it is send out, since this happens via the user's email client. No other information can be send, because the Android permissions for Internet access are not asked by our application.


versionThe version of the application to make sure the data is processed right

number_partners_totalThe number of people with whom communication is documented in the call and message logs

number_partners_without_nameThe number of interaction partners whose names are not in the phone\'s contact list

number_contacts_totalThe number of entries in the contact list

number_calls_totalThe overall number of calls documented in the call logs

number_messages_totalThe overall number of messages documented in the message logs

partners:An anonymized list of your communication partners with the following information:

starredIs 'true' if this contact was tagged with the 'favorite-star' in the contact list

humanIs 'false' if you hit This is not a person durint the rating

index_in_rating_listRepresents the location of this partner in the order of partners to be rated

rating_closenessA number (1-5) representing your rating of this contact concerning the first question (closeness)

rating_trust_informationA number (1-5) representing your rating of this contact concerning the second question (trust with sensitive information)

rating_trust_bestA number (1-5) representing your rating of this contact concerning the third question (trust that the person wants your best)


relative_dateA number representing the time of this call relative to the time of the execution of the app plus a random number [s] (So no actual date and time can be obtained)

durationThe number of seconds this call lasted [s]

call_typeEither 'incoming', 'outgoing', or 'missed'

number_typeThe type of the number as stored in the contact list (e.g., 'home', 'work', ...)


relative_dateA number representing the time of this message relative to the time of the execution of the app plus a random number [s] (So no actual date and time can be obtained)

lengthThe length of the message in number of symbols

message_typeEither 'incoming' or 'outgoing'

number_typeThe type of the number as stored in the contact list (e.g., 'home', 'work', ...)


Sebastian Trapp
Freie Universität Berlin
Computer Systems and Telematics
Takustr. 9
14195 Berlin, Germany
Matthias Wählisch
Freie Universität Berlin
Computer Systems and Telematics
Takustr. 9
14195 Berlin, Germany

[1] Sebastian Trapp, Matthias Wählisch, and Jochen H. Schiller. Short paper: can your phone trust your friend selection?. In Proceedings of the 1st ACM workshop on Security and privacy in smartphones and mobile devices (SPSM '11). ACM, New York, NY, USA, 69-74, 2011.