Arcana: Enabling Private Posts on Public Microblog Platforms

Many popular online social networks, such as Twitter, Tum-blr, and Sina Weibo, adopt too simple privacy models to satisfy users'diverse needs for privacy protection. In platforms with no (i.e., completely open) or binary (i.e., "public" and "friends-only") access con-trol, users cannot control the dissemination boundary of the contentthey share. For instance, on Twitter, tweets in "public" accounts areaccessible to everyone including search engines, while tweets in "pro-tected" accounts are visible toallthe followers. In this work, we presentArcanato enable fine-grained access control for social network content sharing. In particular, we target the Twitter platform and intro-duce the "private tweet" function, which allows users to disseminateparticular tweets to designated group(s) of followers. Arcana employsCiphertext-Policy Attribute-based Encryption (CP-ABE) to implement social circle detection and private tweet encryption so that access-controlled tweets are only readable by designated recipients. To bestealthy, Arcana further embeds the protected content as digital water-marks in image tweets. We have implemented the Arcana prototype asa Chrome browser plug-in, and demonstrated its flexibility and effec-tiveness. Different from existing approaches that require trusted third-parties or additional server/broker/mediator, Arcana is light-weight andcompletely transparent to Twitter - all the communications, includingkey distribution and private tweet dissemination, are exchanged as Twit-ter messages. Therefore, with small API modifications, Arcana could beeasily ported to other online social networking platforms to support fine-grained access control.