Encrypted File System (EFS)

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Encrypted File System (EFS)

• Sankara Narayanan.
• CSE 785 Computer Security,
• Syracuse University, NY
• Spring 2003 2004

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What will be covered!!!refer inline comments

• EFS What is this? A users Perspective.
• Objective
• Motivation
• Related Work and Papers
• Top Notch Encryption Algorithms
• Design and Implementation Ideas Proposed
• Design Issues An Area to be really looked on
• Sample EFS Demo Sites.

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EFSA users perspective.

• Encrypted File System (EFS) provides the core
  file encryption technology used to store
  encrypted files on the File System.
• Corporate world is very competitive, so any code,
  system specifications, often needs to be
  controlled.
• We have to share data among many users or groups,
  the potential risk for a computer security from a
  users perspective.
• Password Security Does nothing to preventing a
  disk being mounted on a different system and
  reading the contents.

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Why EFS Users Perspective..Continued

• The need for Encryption Technology arises from
  the perspective of an user.
• Now many universities and organizations have an
  EFS design for this reason.
• WELCOME TO THE WORLD OF EFS.

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Objectives..

• The Disk Encryption reduce risk of data exposure
  in a specific, if uncommon, scenario.
• To avoid system risks such as
• Computer is bodily stolen.
• Someone inside the company is trying to
  compromise information.
• The system is cracked while attached to a network
  or with some malicious software.
• The primary benefit of the encrypted disk system
  is defense against device theft, and making your
  system a more secured one. Though, the risks are
  partially mitigated.

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MotivationWhy EFS?

• SecurityFirst and Foremost
• Secures Data from being accessed by any malicious
  user / hacker.
• Privacy
• Ensure that private data is not accessed by other
  users ( may not be malicious).
• Reliability An integral component
• Only responsible people are provided access to
  important data
• Resource Sharing
• Many users can use the same system and still can
  work independently.

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Related Work and Papers

• StegFS A Steganographic File System for Linux,
  University of Cambridge.
• CFS Cryptographic File System, Temple
  University.
• SFS Secure File system, University of Minnesota
  and StorageTek.
• TCFS Transparent Cryptographic File System,
  University of Salerno (Italy).
• Cryptfs A Stackable Vnode Level Encryption File
  system, University of Columbia.

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CFS Cryptographic File system refer inline
comments

• CFS File System is implemented on the Debian
  Distribution.
• Completely implemented at the user level.
• CFS runs a daemon cfsdwhich uses the system
  calls to read and write the file contents.
• Encrypted before reading and decrypted before
  writing.
• Simple and Easy to understand.

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TCFS Transparent Cryptographic File System.

• TCFS (Transparent Cryptographic File System) has
  been developed at the University of Salerno
  (Italy) and is currently available for Linux.
• TCFS is like an extended NFS. It acts just like
  NFS, but allows a user to protect his/her files
  using encryption.
• TCFS works as a layer under the VFS (Virtual File
  system Switch) layer, making it completely
  transparent to the applications.

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TCFS Continuedrefer inline comments

• The security is guaranteed by means of the DES
  (data encryption standard) algorithm.
• A TCFS user trust only the kernel and the super
  user of the client machine accessing the data.
• Application areas where TCFS is used a network
  of workstations with limited disk space, each
  used almost exclusively by a limited number of
  users (you can even think of each user as the
  super user of his/her own workstation) and a
  remote file server sharing files with all the
  workstations

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TCFS Continuedrefer inline comments

• The security mechanism must guarantee that secure
  files are not readable
• by any user other than the legitimate owner.
• by tapping the communication lines between the
  user and the remote file system server.
• by the super user of the file system server.
• In TCFS, security acts in a transparent way.
  Secure files can be accessed in the same way as
  local files--the user has only to authenticate
  himself to TCFS before starting to work.

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Working of TCFS
Files stored on Encrypted form in server
Each user has a different Encryption key to
access
TCFS Login Utility Provides Encryption key
Read a block of data from Server NFS Protocol
Requested block is decrypted first and then
passed to application
Data block written by application is first
encrypted with users key and then passed to
server
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StegFS Steganographic File System

• First, like any file system, it is able to manage
  the storage of files on a disk.
• Second, it provides a mechanism for hiding files.
  This allows a user to plausibly deny the number
  of files stored on disk.
• Third, it provides a mechanism for accessing
  files that have been hidden.

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Continued..StegFS

• The file system implementation is installed along
  side the normal Ext2fs, Minix etc drivers between
  the VFS interface and blockbuffer cache.
• StegFS contains the full functionality for Ext2fs
  driver for compatible access to non-hidden files.
• StegFS distinguishes regular files and directory
  files.
• StegFS also has a block allocation table (same as
  block allocation bitmap) for storing encrypted
  checksums for each block.( for detecting
  overwritten blocks).

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Functionality of StegFS

• The confidentiality of all hidden files are
  guaranteed.
• Deletion of hidden or non-hidden leads
  automatically to their secure destruction.
• Users can plausibly deny the number of files
  stored on the disk.
• Lower layers can be voluntarily compromised
  without revealing the higher layers.

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Top Notch Encryption Algorithms

• AES Advanced Encryption Standard (Rijndael).
• DES - Data Encryption Standard (DES) algorithm,
  adopted by the U.S. government in 1977.
• 3DES Triple DES.
• Blowfish

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General Kernel Architecture.
User Process
open(), read(), write(), etc
System Call Interface
VFS
Kernel
Ext2fs
Minix FS
Buffer Cache
Device Driver
Disk Controller
Hardware
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Design and Implementation Ideas..

• Many of the Implementation that we have seen
  here, has a kernel level implementation of the
  file system.
• Certain implementations have also user level
  daemons running that call the kernel level
  programs ( e.g. NFS)
• I am just describing one system architecture,
  each of the project team has to come up with
  their own creative designs.

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Example -- General System Architecture
This blocks data size Encrypted
Data Area
KeyID Each Blocks max Data size Block Size
User Accessible Memory read() write()
Key DB
Key Encryption and
Decryption
Process
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Design Issues..An area to be looked on...

• The file pointer issues.
• Buffer overflow problems how are you going to
  deal with this.
• Key Management An area worth thinking about how
  you will manage your keys.
• What effect does the process like read and write
  have on the files?
• How are you going to define your system policy?
• Problems related with revocation, change
  ownership etc.

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Sample EFS Demo Sites.

• You can run and see how the EFS works, I am
  listing some sample sites
• http//www.geocities.com/openpgp/linux_en.html
• http//www.linux.se/doc/lasg-www/encryption/

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Conclusion.

• Thank You.