Usable Encryption

The need for users to be able to encrypt their online communication and data has never been clearer. This need is driven in part by widespread surveillance of Internet traffic by governments. Furthermore, an ever-increasing amount of data is stored in the cloud and actively mined by cloud service providers. We believe it is imperative that users be able to take control of their online data, deciding when and by whom it can be accessed.

Recently there has been significant research and development into secure messaging1, with several secure chat applications being broadly adopted. While such deployments are promising, they still fail to reach the goal of ubiquitous usable encryption for the masses2. First, unlike email, secure communication using these tools is only possible between users of the same tools. Second, they lack many features users expect in communication tools—e.g., archival, search, spam filtering. Finally, there security is often locked behind options and ceremonies that will only be correctly understood and executed by security experts (if even then).

In our research group, we seek to push forward the frontiers of usable encryption. This includes designing new secure communication tools for email and chat settings, that better meet the needs of real-world users. We also are investigating how to bring content-based encryption to a variety of web applications to allow users and business to use these applications without relinquishing control of their data.

  1. SoK: Secure Messaging. Unger et al. 35th IEEE Symposium on Security and Privacy. IEEE, 2015. 

  2. SoK: Securing Email—A Stakeholder-Based Analysis. Clark et al. Preprint. 


Publications

Journals and Magazines

Abstract: Since the publication of Why Johnny Can't Encrypt there has been interest in creating usable, secure email that is adoptable by the general public. In this article, we summarize research from the usable-security community on this topic, identify open problems, and call for more research on usable key management.
Abstract: Secure email is increasingly being touted as usable by novice users, with a push for adoption based on recent concerns about government surveillance. To determine whether secure email is ready for grassroots adoption, we employ a laboratory user study that recruits pairs of novice users to install and use several of the latest systems to exchange secure messages. We present both quantitative and qualitative results from 28 pairs of novices as they use Private WebMail (Pwm), Tutanota, and Virtru and 10 pairs of novices as they use Mailvelope. Participants report being more at ease with this type of study and better able to cope with mistakes since both participants are “on the same page.” We find that users prefer integrated solutions over depot-based solutions and that tutorials are important in helping first-time users. Finally, our results demonstrate that Pretty Good Privacy using manual key management is still unusable for novice users, with 9 of 10 participant pairs failing to complete the study.

Conferences

Abstract: We conducted a user study that compares three secure email tools that share a common user interface and differ only by key management scheme: passwords, public key directory (PKD), and identity-based encryption (IBE). Our work is the first comparative (i.e., A/B) usability evaluation of three different key management schemes and utilizes a standard quantitative metric for cross-system comparisons. We also share qualitative feedback from participants that provides valuable insights into user attitudes regarding each key management approach and secure email generally. The study serves as a model for future secure email research with A/B studies, standard metrics, and the two-person study methodology.
Abstract: Private Webmail 2.0 (Pwm 2.0) improves upon the current state of the art by increasing the usability and practical security of secure email for ordinary users. More users are able to send and receive encrypted emails without mistakenly revealing sensitive information. In this paper we describe four user interface traits that positively affect the usability and security of Pwm 2.0. In a user study involving 51 participants we validate that these interface modifications result in high usability, few mistakes, and a strong understanding of the protection provided to secure email messages. We also show that the use of manual encryption has no effect on usability or security.
Abstract: This paper reports the results of a survey of 1,976 individuals regarding their opinions on TLS inspection, a controversial technique that can be used for both benevolent and malicious purposes. Responses indicate that participants hold nuanced opinions on security and privacy trade-offs, with most recognizing legitimate uses for the practice, but also concerned about threats from hackers or government surveillance. There is strong support for notification and consent when a system is intercepting their encrypted traffic, although this support varies depending on the situation. A significant concern about malicious uses of TLS inspection is identity theft, and many would react negatively and some would change their behavior if they discovered inspection occurring without their knowledge. We also find that a small but significant number of participants are jaded by the current state of affairs and have lost any expectation of privacy.
Abstract: Secure email is increasingly being touted as usable by novice users, with a push for adoption based on recent concerns about government surveillance. To determine whether secure email is ready for grassroots adoption, we employ a laboratory user study that recruits pairs of novice users to install and use several of the latest systems to exchange secure messages. We present both quantitative and qualitative results from 25 pairs of novice users as they use Pwm, Tutanota, and Virtru. Participants report being more at ease with this type of study and better able to cope with mistakes since both participants are "on the same page". We find that users prefer integrated solutions over depot-based solutions, and that tutorials are important in helping first-time users. Hiding the details of how a secure email system provides security can lead to a lack of trust in the system. Participants expressed a desire to use secure email, but few wanted to use it regularly and most were unsure of when they might use it.
Abstract: A common approach to designing usable security is to hide as many security details as possible from the user to reduce the amount of information and actions a user must encounter. This paper gives an overview of Pwm (Private Webmail), our secure webmail system that uses security overlays to integrate tightly with existing webmail services like Gmail. Pwm's security is mostly transparent, including automatic key management and automatic encryption. We describe a series of Pwm user studies indicating that while nearly all users can use the system without any prior training, the security details are so transparent that a small percentage of users mistakenly sent out unencrypted messages and some users are unsure whether they should trust Pwm. We then conducted user studies with an alternative prototype to Pwm that uses manual encryption. Surprisingly users were accepting of the extra steps of cutting and pasting ciphertext themselves. They avoided mistakes and had more trust in the system with manual encryption. Our results suggest that designers may want to reconsider manual encryption as a way to reduce transparency and foster greater trust.
Abstract: The number of instant messages sent per year now exceeds that of email. Recently users have been moving away from traditional instant messaging applications and instead using social networks as their primary communications platform. To discover attitudes related to instant messaging and its security, we have conducted a user survey. This paper also presents the design of PFC (Private Facebook Chat), a system providing convenient, secure instant messaging within Facebook Chat. PFC offers end-to-end encryption in order to thwart any eavesdropper, including Facebook itself. Finally, we have conducted a usability study of a PFC prototype.

Workshops

Abstract: Messaging applications like SnapChat illustrate that users are concerned about the permanence of information. We find that this concern extends to email. In this paper we present a usability study of an end-to-end secure email tool with the option to securely delete messages. This tool uses ephemeral keys, one per message thread, and default expiration times, with a user prompt to renew or delete keys. Deleting keys causes the messages in the thread to be unreadable for that user. We compare the usability of this tool to a nearly identical tool that uses long term keys and lacks a feature to expire keys. We also interview participants about their email use patterns and attitudes towards information permanence. We find that participants are especially interested in the ability to control the lifetime of an email message. Participants also report trusting the tool that allowed them to make their email messages ephemeral more than the tool that just encrypted their email.

Preprints

Abstract: While email is the most ubiquitous and interoperable form of online communication today, it was not conceived with strong security guarantees, and the ensuing security enhancements are, by contrast, lacking in both ubiquity and interoperability. This situation motivates our research. We begin by identifying a variety of stakeholders who have an interest in the current email system and in efforts to provide secure solutions. We then use the tussle among stakeholders to explain the evolution of fragmented secure email solutions undertaken by industry, academia, and independent developers. We develop an evaluation framework for proposed or deployed secure email systems and identify how well they meet properties related to security, utility, deployability, and usability. We conclude with a fresh look at the state of secure email and discuss open problems in the area.