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Secure messaging tools are an integral part of modern society. To understand users' security and privacy perceptions and requirements for secure group chat, we surveyed 996 respondents in the US and UK. Our results show that group chat presents important security and privacy challenges, some of which are not present in one-to-one chat, such as establishing trust for new group members and filtering shared content. Similarly, we find that the sheer volume of notifications that occur in group chat makes it highly likely that users will ignore important security or privacy notifications. We also find that respondents lack mechanisms for determining which tools are secure and instead rely on non-technical strategies for protecting their privacy---for example, self-filtering and carefully tracking group membership. Next, we conduct cognitive walkthroughs (a form of expert review) for five popular group chat tools, demonstrating that these tools fail to meet many of the needs identified in our survey. As such, there is a need for improved group chat tools that better align with user perceptions and requirements. Based on these findings, we provide recommendations on improving the security and usability of secure group chat.

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