Chapter 1

CS549: Cryptography and Network Security
© by Xiang-Yang Li

Department of Computer Science, IIT
Cryptography and Network Security 1

Notice©
This lecture note (Cryptography and Network Security) is prepared by Xiang-Yang Li. This lecture note has benefited from numerous textbooks and online materials. Especially the “Cryptography and Network Security” 2nd edition by William Stallings and the “Cryptography: Theory and Practice” by Douglas Stinson. You may not modify, publish, or sell, reproduce, create derivative works from, distribute, perform, display, or in any way exploit any of the content, in whole or in part, except as otherwise expressly permitted by the author. The author has used his best efforts in preparing this lecture note. The author makes no warranty of any kind, expressed or implied, with regard to the programs, protocols contained in this lecture note. The author shall not be liable in any event for incidental or consequential damages in connection with, or arising out of, the furnishing, performance, or use of these.

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ABOUT INSTRUCTOR

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About Instructor
 Associate Professor IIT  PhD/MS from UIUC 1997-2000  BS, BE Tsinghua University 1990-1995

 Research Interests:  Algorithm design and analysis  Wireless networks  Game theory  Computational geometry  Contact Information  Phone 312-567-5207  Email: [email protected]  Room 229C, SB
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Office and Office hours
 Office


SB 229C， 10 W 31st Street, Chicago.

 Office hours


Wednesday 4:10PM – 6:10PM.

Or by contact: email [email protected],  phone 312 567 5207


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Who we are and what we do

Prof. XiangYang Li
http://www.cs.iit.edu/~xli http://www.cs.iit.edu/~winet/ [email protected] Stuart Building 229C

Research Interest Overview
 Networks and Algorithms

Wireless Sensor Networks,  Cognitive Networks,  Social Networks


 Topics studied:

Wireless sensor systems for environment monitoring  Theoretical performance studies of


 Wireless networks  Social networks

Hardware/system design and manufacturing  Supported by NSF, NSF China, RGC HongKong


Representative Projects
 Environment monitoring
 Ocean

Sense http://www.cse.ust.hk/~liu/Ocean/index.html  GreenObs http://orbsmap.greenorbs.org/
 Tracking objects: iLight

OceanSense (2007-)

GreenObs (2008-)

About 1000 sensors World largest WSN

Applications

Chicago Waterway System (Water Reclamation Plant)

CWS

Stickney WRP (world largest)

Ammonia sensor

Dissolved Oxygen sensor

Objectives and Challenges
 Objectives:  Protect the health and safety of the public, protect the quality of the water supply source (Lake Michigan), improve the quality of water in water-courses, protect businesses and homes from flood damages;
 Challenges:  Complex system (CWS, WRP, CSO, lake, dame, ….)  Systems built many years ago (from 1930’s to 60’s)  Difficult to meet new regulations and standards (e.g., ammonia, water effluent)  What we can contribute  Real time sensor system, decision optimization

Collaborators

Demo

System examples (iLight) (2009-)

System examples (iLight) (2009-)

More sensor/Adhoc/RFID examples

Sensor Network Controlled Mobile Car

Sensor Network Controlled Mobile Car

Systems Developed (Collaborated with Other Schools)

Mesh Nodes, Sensors

Sensor nodes and Mesh Nodes

Sensor nodes

Other Projects
 BlueSense  BlueSky  WiFace

Theoretical Studies
 Algorithm Design and Analysis of Practical

Questions


Wireless ad hoc networks  Wireless sensor networks  RFID  Cognitive networks  Online optimization (little regret)  Computational geometry  Game theory and its applications  Information theory (such asymptotical behavior of large scale networks)

Where do we publish?
 Journals

IEEE/ACM Transactions on Networking, TPDS, Computers, JSAC,  ACM Transactions, and so on


 Conferences

ACM MobiCom, ACM Mobihoc, ACM STOC, ACM SODA, ACM EC  IEEE INFOCOM, ICNP, ICDCS, and so on


Where do our students go?
 Graduated students (9 PhDs)

Faculty at North Carolina Charlotte, Washington State University, Minnesota State University, BUPT  Researcher at Google,  Game designer  Stock trader


Students (graduated, current)

ABOUT THE COURSE

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About This Course
 Suggested books


Cryptography: Theory and Practice by Douglas R. Stinson CRC press Cryptography and Network Security: Principles and Practice; By William Stallings Prentice Hall



 Handbook

of Applied Cryptography by Alfred J. Menezes, Paul C. van Oorschot and Scott A. Vanstone, CRC Press
 I have electronic version!
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Grading and Others
 Grading (IIT main campus and local)

 

Homework 20% Final Exam 30% (closed book on final exam week, 2012) Group Programming Projects 20% (select your own topic, ),
 Programming project: include a final presentation and demo




Group Paper Presentation 15%:
 Select topics from the list, presentation are in order of topics

Individual Term Paper report 15%
 10-15 pages report of some research results in IEEE format (font size 10)

 India session


Homework 20%, final exam 40%, individual programming projects 25%, individual term paper 15%,

 Policy




Do it yourself Can use library, Internet and so on, but you have to cite the sources when you use this information
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Homeworks
 Do it independently

   

 Staple your solution  For group report,

No discussion No copy Can use reference books
Write your name also,  you could discuss with classmates then write your own group’s report (about 15 pages for the topic you selected)

 For project (presentation

and programming)


Type your solution!



For presentation by main campus students: You SHOULD collaborate with your group member and you SHOULD make enough contributions to get credit Others : do it yourself

• print it then submit
• Or submit it electronically
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Topics
 Introduction  Number Theory  Traditional Methods: secret key system

 Modern Methods: Public Key System
 Digital Signature and others  Other topics:


secret sharing, zero-knowledge proof, bit commitment, oblivious transfer,…

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Organization
 Chapters
      


  



Introduction Number Theory Conventional Encryption Block Ciphers Public Key System Key Management Hash Function and Digital Signature Identification Secret Sharing Pseudo-random number Generation Email Security Others
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Cryptography and Network Security

Introduction
Xiang-Yang Li

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Introduction
The art of war teaches us not on the likelihood of the enemy’s not coming, but on our own readiness to receive him; not on the chance of his not attacking, but rather on the fact that we have made our position unassailable. --The art of War, Sun Tzu 孙子兵法
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Information Security

From wikipedia
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C.I.A
 Confidentiality, Integrity and Availability  Information Systems are decomposed in

three main portions, hardware, software and communications


with the purpose to identify and apply information security industry standards, as mechanisms of protection and prevention, at three levels or layers:
 Physical, personal and organizational

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Various Securities
 Data security


Data security is the means of ensuring that data is kept safe from corruption and that access to it is suitably controlled.

 Computer Security




The objective of computer security includes protection of information and property from theft, corruption, or natural disaster, while allowing the information and property to remain accessible and productive to its intended users. Malware: malicious software
 includes computer viruses, worms, trojan horses, most rootkits, spyware, dishonest adware,

 Network Security


protect the network and the network-accessible resources from unauthorized access, consistent and continuous monitoring and measurement of its effectiveness Cryptography and Network Security

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Network Security
 network security and information security are

often used interchangeably

 network security is generally taken as providing

protection at the boundaries of an organization


Network security starts from authenticating any user, most likely a username and a password An intrusion prevention system (IPS)[2] helps detect and prevent such malware. IPS also monitors for suspicious network traffic for contents, volume and anomalies to protect the network from attacks such as denial of service
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

Criteria for Desirable Cryptosystems
 Confidence in Security established  Is it based on hard or intractable problems?

 Practical Efficiency  Space, time and so on  Explicitness  About its environment assumptions, security service offered, special cases in math assumptions,  Protection tuned to application needs  No less, no more  Security protocols cannot do all: man does what man can do, machine does what machine can do  Openness
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 Or how can I know the method is secure?

Most important
 Security first  Efficiency, resource utilization, and

security tradeoffs


This is especially the case for resource constrained networks such as wireless sensor networks
 Limited power supply (thus limited communication, and computation), limited storage space

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Cryptography
 Cryptography (from Greek

means of converting information from its normal, comprehensible form into an incomprehensible format, rendering it unreadable without secret knowledge — the art of encryption.  Past: Cryptography helped ensure secrecy in important communications, such as those of spies, military leaders, and diplomats.  In recent decades, cryptography has expanded its remit in two ways
 

gráphein, "to write") is, traditionally, the study of

kryptós, "hidden", and

mechanisms for more than just keeping secrets: schemes like digital signatures and digital cash, for example. in widespread use by many civilians, and users are not aware of it.
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Crypto-graphy, -analysis, -logy
 The study of how to circumvent the use of cryptography is

called cryptanalysis, or codebreaking.  Cryptography and cryptanalysis are sometimes grouped together under the umbrella term cryptology, encompassing the entire subject.  In practice, "cryptography" is also often used to refer to the field as a whole; crypto is an informal abbreviation.  Cryptography is an interdisciplinary subject,





linguistics Mathematics: number theory, information theory, computational complexity, statistics and combinatorics engineering

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Close, but different fields
 Steganography  the study of hiding the very existence of a message, and not necessarily the contents of the message itself (for example, microdots, or invisible ink)  http://en.wikipedia.org/wiki/Steganography  Traffic analysis  which is the analysis of patterns of communication in order to learn secret information
 The messages could be encrypted


http://en.wikipedia.org/wiki/Traffic_analysis

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Steganography
 Some techniques

Concealing messages within the lowest bits of noisy images or sound files.  Invisible ink  Concealing data within encrypted data


Polybius square  Hidden messages on messenger's body


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Stenography Example

Last 2 bits

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Tools for Stenography
 http://www.jjtc.com/Steganography/toolm

atrix.htm

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Network Security Model
Trusted Third Party
Principal Principal

(sender)

(receiver)

Security transformation

Security transformation

attacker
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Attacks, Services and Mechanisms
 Security Attacks  Action compromises the information security  Could be passive or active attacks  Security Services  Actions that can prevent, detect such attacks.  Such as authentication, identification, encryption, signature, secret sharing and so on.  Security mechanism  The ways to provide such services  Detect, prevent and recover from a security attack

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Attacks
 Passive attacks


Interception
 Release of message contents  Traffic analysis

 Active attacks


Interruption, modification, fabrication
    Masquerade Replay Modification Denial of service

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Information Transferring

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Attack: Interruption

Cut wire lines, Jam wireless signals, Drop packets,
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Attack: Interception

Wiring, eavesdrop
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Attack: Modification

intercept

Replaced info

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Attack: Fabrication
Ali: this is …

Also called impersonation Ali: this is …
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Attacks, Services and Mechanisms
 Security Attacks  Action compromises the information security  Could be passive or active attacks  Security Services  Actions that can prevent, detect such attacks.  Such as authentication, identification, encryption, signature, secret sharing and so on.  Security mechanism  The ways to provide such services  Detect, prevent and recover from a security attack

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Important Services of Security


Confidentiality, also known as secrecy:


only an authorized recipient should be able to extract the contents of the message from its encrypted form. Otherwise, it should not be possible to obtain any significant information about the message contents. the recipient should be able to determine if the message has been altered during transmission. the recipient should be able to identify the sender, and verify that the purported sender actually did send the message. the sender should not be able to deny sending the message.
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

Integrity:




Authentication:




Non-repudiation:


Secure Communication
 protecting data locally only solves a minor part of

the problem.

 The major challenge that is introduced by the

Web Service security requirements is to secure data transport between the different components.

 Combining mechanisms at different levels of the

Web Services protocol stack can help secure data transport (see figure next page).

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Secure Communication

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Secure Communication
 The combined protocol HTTP/TLS or SSL is often

referred to as HTTPS (see figure). SSL was originally developed by Netscape for secure communication on the Internet, and was built into their browsers. SSL version 3 was then adopted by IETF and standardized as the Transport Layer Security (TLS) protocol.  Use of Public Key Infrastructure (PKI) for session key exchange during the handshake phase of TLS has been quite successful in enabling Web commerce in recent years.  TLS also has some known vulnerabilities: it is susceptible to man-in-the-middle attacks and denial-of-service attacks.
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SOAP security
 SOAP (Simple Object Access Protocol) is designed to pass

through firewalls as HTTP. This is disquieting from a security point of view. Today, the only way we can recognize a SOAP message is by parsing XML at the firewall. The SOAP protocol makes no distinction between reads and writes on a method level, making it impossible to filter away potentially dangerous writes. This means that a method either needs to be fully trusted or not trusted at all.  The SOAP specification does not address security issues directly, but allows for them to be implemented as extensions.


As an example, the extension SOAP-DSIG defines the syntax and processing rules for digitally signing SOAP messages and validating signatures. Digital signatures in SOAP messages provide integrity and non-repudiation mechanisms.

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PKI
 PKI key management provides a sophisticated framework for

securely exchanging and managing keys. The two main technological features, which a PKI can provide to Web Services, are:
 

 Note that the features provided by PKI address the same

Encryption of messages: by using the public key of the recipient Digital signatures: non-repudiation mechanisms provided by PKI and defined in SOAP standards may provide Web Services applications with legal protection mechanisms

basic needs as those that are recognized by the standardization organizations as being important in a Web Services context.  In Web Services, PKI mainly intervenes at two levels:
 

At the SOAP level (non-repudiation, integrity) At the HTTPS level (TLS session negotiation, eventually assuring authentication, integrity and privacy)
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Some basic Concepts

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Cryptography
 Cryptography is the study of


Secret (crypto-) writing (-graphy)

 Concerned with developing algorithms:

Conceal the context of some message from all except the sender and recipient (privacy or secrecy), and/or  Verify the correctness of a message to the recipient (authentication)  Form the basis of many technological solutions to computer and communications security problems


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Basic Concepts
 Cryptography


encompassing the principles and methods of transforming an intelligible message into one that is unintelligible, and then retransforming that message back to its original form The original intelligible message The transformed message Is treated as a non-negative integer hereafter
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 Plaintext


 Ciphertext


 Message


Basic Concepts
 Cipher  An algorithm for transforming an intelligible message into unintelligible by transposition and/or substitution, or some other techniques  Keys  Some critical information used by the cipher, known only to the sender and/or receiver  Encipher (encode)  The process of converting plaintext to ciphertext  Decipher (decode)  The process of converting ciphertext back into plaintext
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Basic Concepts


cipher
 an

algorithm for encryption and decryption. The exact operation of ciphers is normally controlled by a key — some secret piece of information that customizes how the ciphertext is produced



Protocols
specify the details of how ciphers (and other cryptographic primitives) are to be used to achieve specific tasks.  A suite of protocols, ciphers, key management, userprescribed actions implemented together as a system constitute a cryptosystem;  this is what an end-user interacts with, e.g. PGP

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Encryption and Decryption

Decipher P = D(K2)(C) Plaintext ciphertext

Encipher C = E(K1)(P)
K1, K2: from keyspace These two keys could be different; could be difficult to get one from the other
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What is Security?
 Two fundamentally different securities  Unconditional security
 No matter how much computational power is available, the cipher cannot be broken  Using Shannon’s information theory  The entropy of the message I(M) is same as the entropy of the message I(M|C) when known the ciphertext (and possible more)  Given limited computing resources (e.g time needed for calculations is greater than age of universe), the cipher cannot be broken  What do we mean “broken”?  Proved by some complexity equivalence approach



Computational security

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Visual Cryptography
By:

Moni Naor Adi Shamir

Visual Cryptography
 Visual Cryptography is a secret-sharing method that

encrypts a secret image into several shares but requires neither computer nor calculations to decrypt the secret image. Instead, the secret image is reconstructed visually: simply by overlaying the encrypted shares the secret image becomes clearly visible
 A Visual Cryptography Scheme (VCS) on a set Ρ of n

participants is a method of encoding a 'secret' image into n shares such that original image is obtained only by stacking specific combinations of the shares onto each other.

Advantage of Visual Cryptography
 Simple to implement  Encryption don’t required any NP-Hard problem

dependency  Decryption algorithm not required (Use a human Visual System). So a person unknown to cryptography can decrypt the message.  We can send cipher text through FAX or E-MAIL  Infinite Computation Power can’t predict the message.

Introduction:
 Cryptography:

Plain Text Plain Text Channel

Encryption Decryption

Cipher Text

Visual Cryptography:
Plaintext (in form of image)
Encryption (creating shares) Channel (Fax, Email) Decryption (Human Visual System)

Example:
 Secret Image

Share1 Stacking the reveals the

share secret

Share2

Encoding of Pixels:

Original Pixel
Share1 Share2 overlaid

Note: White is actually transparent

Computer Representation of pixels
 Visual Cryptography scheme represented in computer

using n x m Basis matrices

Original Pixel

share1 s1= share2

s0=

overlaid Image

(2,2) Model
1. Construct two 2x2 basis matrices as:

s0=

1 0

0 1

s1= 1 1

0 0

2.Using the permutated basis matrices, each pixel from the secret image will be encoded into two sub pixels on each participant's share. A black pixel on the secret image will be encoded on the ith participant's share as the ith row of matrix S1, where a 1 represents a black sub pixel and a 0 represents a white sub pixel. Similarly, a white pixel on the secret image will be encoded on the ith participant's share as the ith row of matrix S0.

Cont…..
3. Before encoding each pixel from the secret image onto each share, randomly permute the columns of the basis matrices S0 and S1 3.1 This VCS (Visual Cryptography Scheme) divides each pixel in the secret image into m=2 sub pixels.  3.2 It has a contrast of α(m)·m=1 and a relative contrast of α(m)=1/2.