Serverless distributed computing has received significant attention from both the industry and the research community. Among the most popular applications are the wide-area network file systems, exemplified by CFS, Farsite, and OceanStore. These file systems store files on a large collection of untrusted nodes that form an overlay network. They use cryptographic techniques to maintain file confidentiality and integrity from malicious nodes. Unfortunately, cryptographic techniques cannot protect a file holder from a Denial-of-Service (DoS) attack or a host compromise attack. Hence, most of these distributed file systems are vulnerable to targeted file attacks, wherein an adversary attempts to attack a small (chosen) set of files by attacking the nodes that host them.