Explore the challenges and solutions in engineering privacy for contact tracing apps in this 19-minute conference talk from USENIX Enigma 2021. Delve into the complexities of integrating privacy protocols into mobile applications and larger ecosystems involving servers and health services. Learn how privacy engineers navigate obstacles with limited control over key operational components. Discover the innovative approaches used to maintain end-to-end privacy in contact tracing apps, despite working with what the speaker describes as "quicksand." Gain insights into the intricate balance between functionality, security, and user privacy in the development of these critical public health tools.