How Advanced Browsing Protection Works in Messenger

This post details the implementation of Advanced Browsing Protection (ABP) in Messenger, which uses Private Information Retrieval (PIR) and Confidential Computing (AMD SEV-SNP) to protect user privacy while analyzing potentially malicious URLs. It describes the challenges of URL prefix matching in a PIR setting, the development of a server-side ruleset generation process to balance bucket sizes and privacy, and the use of AMD SEV-SNP for secure processing of hash prefixes within a confidential virtual machine. The post highlights tradeoffs between privacy and efficiency in sharding strategies and the need for padding to obscure query lengths.