  Augmented/Mixed Reality (AR/MR) technologies offers a new era of immersive,
collaborative experiences, distinctively setting them apart from conventional
mobile systems. However, as we further investigate the privacy and security
implications within these environments, the issue of gait privacy emerges as a
critical yet underexplored concern. Given its uniqueness as a biometric
identifier that can be correlated to several sensitive attributes, the
protection of gait information becomes crucial in preventing potential identity
tracking and unauthorized profiling within these systems. In this paper, we
conduct a user study with 20 participants to assess the risk of individual
identification through gait feature analysis extracted from video feeds
captured by MR devices. Our results show the capability to uniquely identify
individuals with an accuracy of up to 92%, underscoring an urgent need for
effective gait privacy protection measures. Through rigorous evaluation, we
present a comparative analysis of various mitigation techniques, addressing
both aware and unaware adversaries, in terms of their utility and impact on
privacy preservation. From these evaluations, we introduce GaitGuard, the first
real-time framework designed to protect the privacy of gait features within the
camera view of AR/MR devices. Our evaluations of GaitGuard within a MR
collaborative scenario demonstrate its effectiveness in implementing mitigation
that reduces the risk of identification by up to 68%, while maintaining a
minimal latency of merely 118.77 ms, thus marking a critical step forward in
safeguarding privacy within AR/MR ecosystems.
