1

Network SecurityTools and Techniques

Mohamed M. HefeedaMohamed M. Hefeeda

Supervised By: Prof. Reda Ammar

September 2000

2

???? Motivations ????

• How does my bank secure my online transactions?

• How does ___.com protect my credit card if I order online?

• How can an enterprise build a secure private network to link its distributed sites?

• How can we send e-mails that contain secret or sensitive data over the insecure Internet?

• How …..?

• They usually say: Don’t Worry, we use Cryptography, 128-bit encryption, SSL, SET, …!!

• Well, but how???????????

3

Outline

• Part I: Applied Cryptography– The Tools

• Part II: Network Security Techniques– How to use the Tools to build secure systems

• Part III: Mobil Code Security – New evolving technology which has many potential

applications but security is a major issue/problem

4

Outline (contd.)

• Part I: Applied Cryptography (The Tools)– Conventional Cryptography (Private- or Symmetric-key)

• Concepts/Principles

• DES, 3-DES, IDEA, CAST, Blowfish, RC2, RC5, ….

– Public-key Cryptography• Concepts/Principles

• RSA, ElGamal, Diffie-Hellman, …

– Message Digest (One-way Hash algorithms)• MD5 and SHA

– Digital Signature• DSS (based on ElGamal and Schnor scheme) and RSA

– Message Authentication Code (MAC)• HMAC

– Cryptographic Pseudorandom Number Generators• Blum-Blum-Shub, ANSI X9.17, ...

5

Outline (contd.)

• Part II: Network Security (The Techniques)– Authentication Protocols:

• Kerberos and X.509 Authentication services

– Web Security:• SSL and SET

– E-mail Security:• PGP and S/MIME

– IP Security

– Biometrics

– Smartcards

– Languages which support Security• Java Security Model

– Case Study (Windows 2000 Security Features)• Kerberos, Public-Key Infrastructure, Encrypted File System, ...

6

Outline (contd.)

• Part III: Mobile Code Security– Mobile Agents

• Concepts, applications, and Security Issues

– Protecting the host from the visiting agents• Sandboxing

• Digital-Shrink Wrap

• Proof-Carrying Code

– Protecting the agent during the transfer• Passive attacks

• Active attacks

– Protecting the agent from the Host• Limited Backbox

• Computing with encrypted functions

• Cryptographic traces

7

Conventional Cryptography: Concepts

• One Key:– used for both encryption and decryption (symmetric)

– Alice and Bob meet in private and agree on a key

• Principles:– Confusion

• The ciphertext should depend on the plaintext and the key in a complicated and involved manner. (done through substitution)

• Objective: hide how the statistics of the ciphertext depend on the statistics of the plaintext

– Diffusion• Each plaintext bit should affect every (or as many as possible) of the

ciphertext bits. (done through permutation or transposition)

8

Conventional Cryptography: DES

• Data Encryption Standard (DES)– Late 60’s: IBM developed LUCIFER encryption algorithm

– In 1973: NIST accepts IBM’s proposal as a national cipher standard

– In 1977: After refinement, DES became the standard

• Description:– Plaintext X; |X| = 64 bits, X = L0R0

– Key K; |K|= 56 bits

– Three stages:• IP: Initial Permutation, X0 = IP(L0R0)

• 16 iterations of a certain function, F

• IP-1: Y = IP-1(L16R16)

9

DES: Encryption

Initial Permutation

Round 1

Round 2

Round 16

32-bit swap

Inverse Initial Permutation

GenerateSub-keys

K1

K2

K16

56-bit key64-bit plaintext

64-bit ciphertext

• Decryption: same procedure but reverse the order of the sub-keys

10

DES: Single Round

F

+

Ki

Ri-1Li-1

RiLi

Li = Ri-1

Ri = Li-1 F(Ri-1 , Ki)

11

DES: Single Round (contd.)

12

DES: S-Boxes

13

DES: Security Strength

• The security of DES is based on the design of the S-boxes, which is NOT publicly published!

• Some suspicious that S-boxes were designed with some trapdoors that might allow their designers (NIST) to break the system

• Exhaustive search needs 256 no longer secure

• Hence, other algorithms are proposed:– 3-DES: with two (112 bits)and three keys (168 bits).

• Encryption: Ek1-> Dk2

->Ek3 • Decryption: Dk3->Ek2->Dk1

– Blowfish: fast, secure, variable length key (32 to 448)

– IDEA: key is 128-bit

– CAST: key is 128-bit, used in PGP

14

Public-key Cryptography: Concepts

Encryption Algorithm

Decryption Algorithm

Public Keys(Trusted Party)

Certificate Authority, e.g. VeriSign, CertCo, ...

Alice

M

Bob

C= EKUB(M) M=DKRB

(C)

Plaintext Ciphertext

RegistrationRead/Verify Bob’s public key

• Two keys: (Asymmetric)

— public: used for encryption

— private: used for decryption

Private Key

15

Public-key Cryptography: RSA

• Based on the “Factoring is Hard” assumption

• Key generation:– select p, q large primes, let n= p*q

– select e where: gcd ((n), e) = 1. ( (n) = (p-1)(q-1) )

– compute the private key, d = e-1 mod (n)

– public key: {e, n}

• Encryption– C = Me (mod n)

• Decryption:– M = Cd (mod n)

16

Network Security:Authentication Techniques

• Authentication: prove your identity usually by:– knowing a shared secret (conventional cryptography) or

– signing a message using your private key (public-key cryptography)

• Kerberos Authentication Protocol (MIT)– Two versions: ver 4 (still widely used) and ver 5 (future)

– Uses DES

– Four entities:• Client (C): requesting for a service

• Server (V): providing the service

• Authentication Server (AS): knows all passwords. Shares a unique secret key with each server.

• Ticket-Granting Server (TGS): issues tickets to users who have been authenticated by AS to access a certain service on a certain server V.

17

Kerberos: overview

18

Kerberos: messages exchange

Table 1. Summary of Kerberos Ver 4 Messages Exchange

(a) Authentication service Exchange: to obtain ticket granting ticket

(1) C AS: IDc || IDtgs || TS1

(2) AS C: Ekc[Kc,tgs || IDtgs || TS2 || Lifetime2 || Tickettgs]

Tickettgs = Ektgs[Kc,tgs || IDc || ADc ||IDtgs || TS2 || Lifetime2]

(b) Ticket-Granting Service Exchange: to obtain service-granting ticket

(3) C TGS: IDv || Tickettgs || Authenticatorc

(4) TGS C: Ekc,tgs[Kc,v || IDv || TS4 || Ticketv]

Tickettgs = Ektgs[Kc,tgs || IDc || ADc ||IDtgs || TS2 || Lifetime2]

Ticketv = Ekv[Kc,tgs || IDc || ADc ||IDv || TS4 || Lifetime4]

Authenticatorc = Ekc,tgs[IDc || ADc || TS3]

(c) Client/Server Authentication Exchange: to obtain service

(5) C V: Ticketv || Authenticatorc

(6) V C: Ekc,v[TS5+1]

Ticketv = Ekv[Kc,v || IDc || ADc ||IDv || TS4 || Lifetime4]

Authenticatorc = Ekc,v[IDc || ADc || TS5]

19

Network Security: Web Security

• Security threats:– Passive attack (eavesdropping)

– Active attacks (modify data)

• Security approaches:– Secure Socket Layer. (just above the Transport Layer)

– Secure Electronic Transaction (in the Application Layer)

– Using the IP Security (Network Layer)

20

Network Security: SSL

• Secure Socket Layer (SSL)– Originated by Netscape

– Supports security over the Internet and Intranets

– Provides:• Authentication

– using certificates (public key)

• Confidentiality (encryption)– DES40, DES, 3DES, IDEA, RC2, RC4, and Fortezza

• Integrity (MAC uses one of the following)– MD5 (128-bit hash)

– SHA (160-bit hash)

21

SSL: overview

SSL Protocol Stack

22

SSL: Handshake Protocol

SSL Handshake Protocol Summary

• Used for Authentication and Key exchange

23

SSL: Record Protocol

SSL Record Protocol Operations

• Provides confidentiality and message integrity

24

Network Security: Biometrics

• Authentication/identification approaches based on:– Something you know, e.g. password, PIN number, ...

– Something you have, e.g. ATM card, physical key, …

– Something you are, e,g. biometrics: fingerprint, …

• Biometrics: authenticate individuals based on their biological and/or behavioral characteristics– fingerprint matching

– Iris scanning

– Hand geometry matching

– Retina scanning

– Face recognition

– voice recognition

– DNA, …..

25

Biometrics: system architecture

BiometricReader

FeatureExtractor

BiometricReader

FeatureExtractor

FeatureMatcher

User

Database

Enrollment Phase

Identification Phase

User

Store

Restore

A typical biometric system

26

Case Study: Windows 2000

• Security Features:– Kerberos ver 5 authentication protocol

• Faster, more efficient, and more secure than NTLM

– Encrypted File System (EFS)• transparent to the user• public- and private- key encryption• encrypts the file using DES• encrypts the key of the DES using the user’s private key

– Public-key based protocols• SSL/TLS• Certificate Server

– IP Security (IPSec)• to build a Virtual Private LAN