Metal: A Metadata-Hiding File-Sharing System
Weikeng Chen, Raluca Ada Popa · 2020
File-sharing systems like Dropbox offer insufficient privacy because a compromised server can see the file contents in the clear.Although encryption can hide such contents from the servers, metadata leakage remains significant.The goal of our work is to develop a file-sharing system that hides metadataincluding user identities and file access patterns.Metal is the first file-sharing system that hides such metadata from malicious users and that has a latency of only a few seconds.The core of Metal consists of a new two-server multi-user oblivious RAM (ORAM) scheme, which is secure against malicious users, a metadata-hiding access control protocol, and a capability sharing protocol.Compared with the state-of-the-art malicious-user filesharing scheme PIR-MCORAM (Maffei et al.'17), which does not hide user identities, Metal hides the user identities and is 500× faster (in terms of amortized latency) or 10 5 × faster (in terms of worst-case latency).