EFS: Encrypted File system

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EFS Encrypted File system

• An Introduction Final Project
• For
• CSE785 Computer Security
• Syracuse University
• Spring 2005

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Overview

• EFS What? Why?
• Related Work
• Project Introduction
• Background
• Encryption/Decryption algorithms
• Mounting file system
• Minix System Call
• Project Requirement
• Some design implementation ideas
• My help session topics
• Conclusion

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EFS what is it?

• 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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EFS why do we need it?

• 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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EFS benefits

• 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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EFS a definition from whatis.com

• The Encrypting File System (EFS) is a feature of
  the Windows 2000 operating system that lets any
  file or folder be stored in encrypted form and
  decrypted only by an individual user and an
  authorized recovery agent. EFS is especially
  useful for mobile computer users, whose computer
  (and files) are subject to physical theft, and
  for storing highly sensitive data. EFS simply
  makes encryption an attribute of any file or
  folder. To store and retrieve a file or folder, a
  user must request a key from a program that is
  built into Windows 2000.
• Although an encrypting file system has existed in
  or been an add-on to other operating systems, its
  inclusion in Windows 2000 is expected to bring
  the idea to a larger audience.

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Related work

• 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).

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Project Introduction

• In this project, we would like you to
• Design a scheme to add security features to the
  existing file system and
• Devise ways to encrypt / decrypt files using the
  encryption algorithms

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Background Knowledge Encryption/Decryption
Algorithms

• Two types of Encryption/Decryption Schemes
• Symmetric Key (Secret-key) Scheme
• DES Data Encryption Standard
• AES Advanced Encryption Standard
• Asymmetric Key (public-key) Scheme
• RSA reinvented by Rivest, Shamir, and Adleman
• ECC Elliptic Curve Cryptography

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Symmetric Key Algorithms

• A symmetric-key algorithm is an algorithm for
  cryptography that uses the same cryptographic key
  to encrypt and decrypt the message. (Actually, it
  is sufficient for it to be easy to compute the
  decryption key from the encryption key and vice
  versa.)
• Other terms for symmetric-key encryption are
  single-key and private-key encryption

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AES Algorithm

• Advanced Encryption Standard, a symmetric 128-bit
  block data encryption technique developed by
  Belgian cryptographers Joan Daemen and Vincent
  Rijmen.
• AES works at multiple network layers
  simultaneously.
• The U.S government adopted the algorithm as its
  encryption technique in October 2000, replacing
  the DES encryption it used.
• The National Institute of Standards and
  Technology (NIST) of the U.S. Department of
  Commerce selected the algorithm, called Rijndael,
  out of a group of five algorithms under
  consideration, including one called MARS from a
  large research team at IBM.

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Asymmetric Key Algorithms

• An encryption method that uses a two-part key a
  public key and a private key.
• To send an encrypted message to someone, you use
  the recipient's public key, which can be sent to
  you via regular e-mail or made available on any
  public Web site or venue.
• To decrypt the message, the recipient uses the
  private key, which he or she keeps secret.
  Contrast with "secret key cryptography," which
  uses the same key to encrypt and decrypt
• Usually we call it Public Key algorithms

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Background Knowledge Mounting File System

• All files accessible in a Unix system are
  arranged in one big tree, the file hierarchy,
  rooted at /. These files can be spread out over
  several devices.
• The mount command serves to attach the file
  system found on some device to the big file tree.
  
• Conversely, the umount command will detach it
  again.

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Background Knowledge System Call Implementation

• We expect the implementation in kernel level, so
  you should make use of system calls
• On how to implement system calls, please refer to
  materials in help session 3 system call creation
  implementation

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Project Requirements

• We expect you to design and implement a working
  encrypted file system for the Minix operating
  system, which includes
• Individual users should have their keys for
  encrypting and decrypting files
• Key management in the system
• File management
• Authenticate the user trying to login to the
  system

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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..areas 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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Refer to some other EFS systems

• As mentioned in the related work slide
• 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).

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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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My help session topics

• Temporarily, I have the following schedule for
  the help session before project due
• Location Star Lab in CST 1-120
• Time The following afternoons 100400pm
• Schedule
• 04/14 AES algorithms
• 04/21 Mounting your file system
• 04/28 File system management
• 05/05 Last minute rush
• May change according to your feedback

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Thank you Good luck!