Hi, Some of you have sent me mail asking about my cryptographic file system for Unix; it was the subject of a work-in-progress presentation at the January Usenix conference. I have a draft of a paper that you may find helpful; I just got off the phone with our lawyer and finally have the release to send it out, so if you'd like a copy of the draft, send me your email (for postscript) or physical (for dead trees) address. Before you ask: the software also may be released, but that's a longer process and it isn't really "ready for prime time" yet anyway. The paper is just a draft, and also has some bugs in it, but some of it seems relevant to the discussion here on similar projects for PCish machines. Here's the abstract: ======== Although cryptographic techniques are playing an increasingly important role in modern computing system security, user-level tools for encrypting file data are cumbersome and suffer from a number of inherent vulnerabilities. The Cryptographic File System (CFS) offers an alternative to ad hoc user-level encryption for protecting file data. CFS supports secure storage at the system level through a standard Unix file system interface to encrypted files. Users can associate a cryptographic key with any directories they wish to protect. Files in these directories (as well as their pathname components) are transparently encrypted and decrypted with the specified key without further user intervention; cleartext is never stored on a disk or sent to a remote file server. CFS can use any available file system for its underlying storage without modification, including distributed file systems such as NFS. System management functions, such as file backup, work in a normal manner and without knowledge of the key. This paper describes the design and implementation of CFS under Unix. Encryption techniques for file system-level encryption are described, and general issues of cryptographic system interfaces to support routine secure computing are discussed. ======== -matt mab@research.att.com