EFS: Encrypted File system
An Introduction & Final Project
For
CSE785: Computer Security
Syracuse University
Spring 2005
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
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.
EFS: why do we need it?

Security—First and Foremost


Privacy


Ensure that private data is not accessed by other users (
may not be malicious).
Reliability – An integral component


Secures Data from being accessed by any malicious user
/ hacker.
Only responsible people are provided access to
important data
Resource Sharing

Many users can use the same system and still can work
independently.
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.
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.
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).
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
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
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

AES Algorithm

Advanced Encryption Standard, a symmetric 128bit 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.
Asymmetric Key Algorithms

An encryption method that uses a twopart 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
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.
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
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
General Kernel Architecture.
open(), read(), write(), etc
User Process
System Call Interface
VFS
Minix FS
Kernel
Ext2fs
Buffer Cache
Device Driver
Disk Controller
Hardware
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.

Example -- General System
Architecture
KeyID
Each Blocks max
Data size
Block Size
This blocks data
size
Encrypted Data
Area
User Accessible Memory
read()
write()
Key DB
Key
Encryption and
Decryption
Process
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.
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).
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.h
tml
http://www.linux.se/doc/lasg-www/encryption/
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 1:00~4:00pm
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

Thank you & Good luck!