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Exploring User Mental Models of End-To-End Encrypted Communication Tools

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Exploring User Mental Models of End-To-End Encrypted Communication Tools Exploring User Mental Models of End-to-End Encrypted Communication Tools Ruba Abu-Salma Elissa M. Redmiles Blase Ur, Miranda Wei University College London University of Maryland University of Chicago Abstract a key obstacle to the adoption of secure communication tools and other privacy-enhancing technologies [1, 26]. End-to-end (E2E) encrypted communication tools can Prior qualitative work has explored users’ familiarity help users keep their communications secure from gov- with secure communication tools and gaps in their men- ernment or corporate surveillance. In this work, we con- tal models [1]. In our work, we seek to quantitatively duct a quantitative survey (n=125) to assess general men- validate and expand on these findings. We do so by tal models and understandings of a hypothetical E2E en- studying both users and non-users via a quantitative sur- crypted communication tool. We find that the vast ma- vey through which we assess high-level mental models jority of respondents had adopted E2E encrypted tools of E2E encryption and its security properties. We fo- in the real world, but lacked confidence and accuracy in cus specifically on one type of secure communication, their mental models of E2E encryption. Two key mis- E2E encrypted communication, abstracted away from conceptions include (1) three-quarters of respondents be- detailed predispositions of any specific tool created by lieving that their E2E encrypted communications could any particular brand. be accessed by unauthorized entities, and (2) one-half of To this end, we surveyed 125 respondents about a hy- respondents feeling that SMS and landline phone calls pothetical E2E encrypted communication tool. The de- were more secure than, or as secure as, E2E encrypted scription of our hypothetical tool was based on a system- communications. These findings raise concerns that re- atic review of the descriptions of 20 real E2E encrypted spondents may not feel threatened by proposals of “back- communication tools (e.g., WhatsApp, Telegram); we doors” since they already feel that different entities can chose this method in order to minimize bias from brand- access their communications. More broadly, our findings based perceptions of specific tools. Using this hypotheti- suggest that the primary user-related challenge for E2E cal tool as a foundation, we explore people’s understand- encrypted tools may no longer be adoption, but helping ing of E2E encryption and the security properties of E2E users who already have these tools avoid sending sensi- encrypted communication tools. tive information over less secure channels. The majority of respondents currently use at least one E2E encrypted tool, most frequently WhatsApp. Only 1 Introduction 12%, however, felt they could confidently explain E2E encryption. Most surprisingly, only one-quarter of our Secure communication tools empower people to resist respondents believed that no one could compromise the surveillance. Encrypted email was one of the first forms security of communications in our hypothetical tool. of secure communication; it was followed by Off-the- This is concerning, because a belief that E2E encrypted Record (OTR) messaging [7], which then spawned a va- tools are already insecure could mislead users about the riety of secure communication tools (e.g., Signal). Such danger of proposed measures that would build in insecu- tools offer various security properties such as confiden- rity (e.g., backdoors). tiality (secrecy of communication), integrity (accuracy Further, one-half of respondents mistakenly thought and completeness of communication), and user authen- that SMS messages and landline phone calls would be tication. Secure communication tools are critical for ac- more secure than, or as secure as, E2E encrypted com- tivists, journalists, and others who seek to avoid corpo- munications. Such misunderstandings may lead users to rate or government surveillance. unknowingly select insecure communication tools in sit- Prior work has shown that incorrect mental models are uations where they most require privacy. In some cases (e.g., activists communicating under threat of imprison- models, and a lack of understanding of the email ar- ment or death), such mistakes can be life-threatening. chitecture. They concluded that security researchers Overall, our results suggest that E2E encrypted tools should focus on building “comprehensive mental models are widely used but not accurately understood. Thus, of email security,” but did not study these mental models. the key struggle for E2E encrypted communication tools Further, investigations by De Luca et al. found that peer may no longer be spurring adoption, but emphasizing ap- influence was the primary driver of instant messenger propriate use, by helping users send sensitive informa- adoption, regardless of whether such messengers (e.g., tion using only secure tools. Threema) were advertised as secure or private [11]. Most relevant to our work, Abu-Salma et al. inter- viewed users of different communication tools about 2 Related Work their experiences with those tools and their perceptions of the tools’ security properties [1]. They found that Poor usability has traditionally hampered the adoption barriers to adoption include small and fragmented user and use of secure communication tools. In their seminal bases, lack of interoperability, low QoS (Quality of Ser- paper, Whitten and Tygar found that only one-third of vice), and incorrect mental models of how secure com- respondents were able to use PGP correctly [35]. They munication works. We build on Abu-Salma et al.’s qual- concluded that making secure email usable requires the itative work to conduct a quantitative survey of both refinement of user interface design principles. Addi- users’ and non-users’ mental models of E2E encrypted tional studies have evaluated the usability of other se- communication tools. cure mail systems as well as various user interface prin- ciples, finding that transparency into system operation – 3 Methodology e.g., showing ciphertext after encryption – was particu- larly effective [19, 27, 29]. We conducted an online survey of 125 people in the UK Bai et al. investigated mental models of non-expert in April 2018. Our institution’s Research Ethics Team users when making security and privacy trade-offs approved this study. In this section, we describe the sur- between two encryption models: a traditional key- vey methodology, details of our data analysis, and limi- exchange model (analogous to PGP) and a registration tations of our work. model (analogous to iMessage) [5]. They found that re- spondents understood both models fairly well, but pre- ferred the more usable, but less secure, model even for 3.1 Survey Methodology very sensitive communications. The survey questionnaire was developed through an iter- Other studies [4, 18, 28, 30, 32] have considered PGP ative process. further, as well as explored usability and user under- standing of contact verification in OTR [3], secure com- 3.1.1 Questionnaire Structure munications in two-way radios [9], opportunistic email encryption [17], and public-key fingerprints [12,34]. The We asked respondents to answer questions about a hy- majority of these were lab-based studies, where partici- pothetical E2E encrypted tool. We chose to use a hy- pants were asked to complete a specific set of tasks. pothetical tool to avoid bias from respondents’ precon- Additional work has employed qualitative methods ceived notions of specific tools or tool providers. We in- to understand why people use, or do not use, secure troduced respondents to this tool using the following de- communication tools. Gaw et al. conducted a quali- scription: “Imagine you are considering using a new tool tative study to explore users’ decisions about whether named Soteria to communicate with your family mem- and when to encrypt emails [20]. They interviewed bers, friends, work colleagues, and others. When you nine members of an activist organization under the pre- install Soteria, the following message is displayed: ‘So- sumption that the organization’s employees would have teria communications (messages, phone calls, and video a strong incentive to encrypt emails. Instead, they found calls) are end-to-end encrypted.’ ” that participants’ perceptions of those who used en- We constructed the Soteria message (i.e., the itali- 1 crypted email (i.e., only “paranoid people” or “people cized text) by conducting a cognitive walkthrough of the who are up to no good”) influenced participants’ deci- 1Cognitive walkthroughs are a usability inspection method actively sions to use encryption. used in human-computer interaction research to identify and evaluate Renaud et al. interviewed non-expert students and staff design components [23]. In our case, we sought to identify how infor- members, as well as computer science students [26]. mation about message security and privacy was conveyed to the user. For example, WhatsApp advertises itself as E2E encrypted by display- They found that the key barriers to the adoption of E2E ing a message when the user begins a chat, which explains that mes- encrypted email were usability issues, incomplete threat sages sent using WhatsApp “are secured using end-to-end encryption.” user interfaces of 20 different communication tools in- Gender Age Race Education Employment cluded on the Electronic Frontier Foundation (EFF) Se- Male 18–24 Black B.Sc. Student cure Messaging Scorecard [14]. We then worded the So- Male 18–24 White B.Sc. Student teria display message to closely match wording used by Male 25–34 Hispanic M.Sc. Employed the majority of tools (e.g., WhatsApp, Telegram) to ad- Male 25–34 White Ph.D. Student Male 35–44 Black B.Sc. Employed vertise, or provide feedback to users about, the security Male 35–44 White Some college Employed of their communications. We asked respondents to an- Male 45–54 Asian M.Sc. Employed swer a list of questions about Soteria based on one of the Male 55–64 Black Some college Unemployed Female 18–24 Asian B.Sc. Student scenarios below (randomly assigned to each respondent) Female 18–24 Black M.Sc.
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