Fast Secure File System 0.0.2 review

Fast Secure File System exports existing directories securely over the network, letting users store and retrieve encrypted data in a

License: GPL (GNU General Public License) File size: 0K Developer: Nicola Cocchiaro

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Fast Secure File System exports existing directories securely over the network, letting users store and retrieve encrypted data in a scalable and transparent way. FSFS is written in C and works on GNU/Linux systems on x86 and PPC architectures, with help from FUSE and OpenSSL.

File systems are easily the most evident, from the point of view of users, component of an operating system. Through file systems it is possible to organize data in a wide variety of ways, and access resources through a common interface.

Users can nowadays not only store and retrieve documents, but also find information on running processes and system settings (through ProcFS), access and manipulate e-mail (for example with GmailFS), or perform several other operations.

In several circumstances and scenarios it is desirable to protect stored files and directories from manipulation by unknown or malicious users: financial or health-related data, confidential documents, or any kind of personal or sensitive data may need to be stored securely, in such a way that it can not be examined or modified freely by third parties.

Most file systems do not take action in this sense, and external cryptographic utilities are sometimes employed to secure data before storage. While this can be a perfectly secure solution, it is not transparent to users.

Distributed file systems propose efficient ways of accessing data remotely as if it resided on the local machine; when it comes to dealing with securely stored data as in the examples above, care must be taken to preserve confidentiality and integrity also during network transfer.

Not all distributed file systems accomplish this task, weakening the overall security of the system, or do so inefficiently, making it inconvenient for users.

FSFS is a secure, distributed file system in users space, written in C with much help from FUSE and OpenSSL. It lets users store and retrieve data securely and transparently, knowing that it is protected both on permanent storage devices and while in transit over the network.

It is also concerned with scalability, therefore separates data cryptography from the server, leaving it to the clients; this approach is similar to the one used in CFS, and opposite to those taken on by other secure file system solutions (like NFS on top of IPsec).

FSFS is written as a pair of user space daemons that act as client and server. Because of this, it needs no kernel support (unlike NFS over IPsec), save the FUSE loadable kernel module on clients, included in Linux since 2.6.14; servers don't use FUSE and depend only on user space OpenSSL libraries.

Servers export an existing file system (of virtually any kind) to clients over the network through two separate channels: a TLS connection set up with OpenSSL, and a clear channel. Requests from the clients to the servers are sent via the TLS socket, thus they are encrypted and authenticated, according to TLS v1 specifications, by the channel itself and decrypted on receipt, as they are usually very short and the relevant cryptography does not constitute a great overhead; simple server replies undergo the same process.

Cryptography in this case happens at both ends of the transmission.
In a distributed file system, large amounts of data may be transferred between clients and servers, thus encrypting and decrypting everything may become too cumbersome for both parties, and as more clients are added to the system the server may severely lose performance; moreover, file data should be stored encrypted anyway, so the cryptography could be moved to the clients, in such a way that each encrypts data before a write operation sends it over the network to the server, and decrypts it after a read retrieves it.

This way servers only deal with TLS details and can concentrate on serving client requests by doing the relevant I/O on the underlying, "physical" file system. As the data is already encrypted, it does not need to go through the TLS channel and the corresponding overhead, but can be sent via the clear channel, provided the messages are authenticated.