  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 user
interface traits that positively affect the usability and security of Pwm 2.0:
(1) an artificial delay to encryption that enhances user confidence in Pwm 2.0
while simultaneously instructing users on who can read their encrypted
messages; (2) a modified composition interface that helps protect users from
mistakenly sending sensitive information in the clear; (3) an annotated secure
email composition interface that instructs users on how to correctly use secure
email; and (4) inline, context-sensitive tutorials, which improved view rates
for tutorials from less than 10% in earlier systems to over 90% for Pwm 2.0. In
a user study involving 51 participants we validate these interface
modifications, and also show that the use of manual encryption has no effect on
usability or security.
