Security School of Business Eastern Illinois University © Abdou Illia, Fall 2002 (Week 12, Wednesday 11/13/2002)

2 Learning Objectives n Understand standard systems attack n Describe Encryption-Decryption techniques

3 Standard systems attacks n Denial of service attacks, or distributed denial of service attacks: – Bombard a site (usually a server or a router) with so many messages that the site is incapable of answering valid requests n Stealing and intercepting passwords and confidential messages.

4 Denial-of-Service (DoS) Attacks n Make the system unusable (crash it or make it run very slowly) by sending a stream of messages. Message Stream DOS Attack (Overloads the Victim) ServerAttacker

5 Distributed DoS (DDoS) Attack Messages Come from Many Sources Server Message Stream Computer with Zombie Computer with Zombie Attacker Attack Command Attack Command n Attacker hacks into multiple clients and plants Zombie programs on them n Attacker sends commands to Zombie programs which execute the attacks

6 Identifying Victims for DDoS n Sending scanning messages – Ping messages (To know if a potential victim exist) – Supervisory messages (To know if victim available) – Etc. n Examining data that responses reveal n IP addresses of potential victims n What services victims are running; different services have different weaknesses n Host’s operating system, version number, etc.

7 Identifying Victims for DDoS n Now you can remotely monitor (in real time) your employee, spouse, child or love interest without even having access to their computer!! n iSpy will allow you to send a tiny file to any computer via which will install this software on the users system. You can then access the users hard drive, listen to the audio of the computer, view screenshots, keystrokes, chats, instant messages, s, and much... much more! You will not find this with any other software!

8 Intercepting confidential messages Attacker Taps into the Conversation: Tries to Read Messages Client PC Server Message Exchange

9 Encryption and Decryption techniques n Cryptography is the study of creating and using encryption and decryption techniques. Plaintext is the data before any encryption has been performed Ciphertext is the data after encryption has been performed The key is the unique piece of information that is used to create ciphertext and decrypt the ciphertext back into plaintext

10 Encryption and Decryption techniques n Key = COMPUTER SCIENCE n Plaintext = this is the account number you have requested n Algorithm based on Vigenere matrix

11 Encryption and Decryption techniques 1) Look at the first letter in the plaintext (T) 2) Look at the corresponding key character immediately above it (C) 3) C tells us to use row C of Vigenere matrix to perform alphabetic substitution for plaintext character T 4) Go to column T in row C and find the cipher character V 5) Repeat Steps 1 through 4 for every character of the plaintext. COMPUTERSCIENCECOMPUTERSCIENCECOMPUTERSCIENCE Thisistheaccountnumberyouhaverequested

12 Encryption and Decryption techniques n Encryption algorithm cannot be kept secret n Key must be kept secret PlaintextEncryptionCiphertextDecryptionPlaintext Algorithm Key Algorithm Key TransmittedOriginal Message Original Message

13 Encryption: Key Length n Key can be “guessed” by exhaustive search – Try all possible keys – See which one decrypts the message n Long keys make exhaustive search difficult – If length is n bits, 2 n tries may be needed – If key length is 8 bits, only 256 tries maximum – Usually, Key Length ≥ 56 bits Assume a key is 56 bits. If it takes seconds to try each key, how long will it take to try all possible keys? What if computers are working together to try all key combinations?

14 Two general Encryption-Decryption methods n Symmetric key encryption method – Use a single key for Encryption-Decryption – Examples: Data Encryption Standard (DES), 3DES n Public key encryption method – Use different keys for Encryption-Decryption – Examples: RSA, Elliptical curve cryptosystem

15 Symmetric key Encryption-Decryption n Symmetric key must be distributed secretly between partners n When Partner A sends to Partner B n Partner A encrypts with the key, partner B decrypts with the key n When Partner B send to Partner A n Partner B encrypts with the key, partner A decrypts with the key PlaintextEncryptionCiphertextDecryptionPlaintext Transfer $5,000 Transfer $5,000

16 Symmetric key Encryption-Decryption n Advantages: n Simple enough for fast Encryption-Decryption n Fast enough for long messages n Disadvantages: n Need a different Symmetric key for each partner (or other partners could read messages) n If N partner, need N*(N-1)/2 keys. PlaintextEncryptionCiphertextDecryptionPlaintext Transfer $5,000 Transfer $5,000

17 Public key Encryption-Decryption n Each partner has a private key (kept secret) and a public key (shared with everybody) n Sending n Partner A encrypts with the public key of Partner B n Partner B encrypts with the public key of Partner A n Receiving n Each receiver decrypt with its own private key Encrypt with Party B’s Public Key Partner A Partner B Decrypt with Party B’s Private Key

18 Public key Encryption-Decryption n Advantages: n Once the message is encrypted, nobody can decrypted it except the receiver n Simplicity of key exchange: No need to exchange public key securely n Disadvantages: n Complex: Requires many computer processing cycles to do Public Encryption- Decryption n Can only be used to encrypt small messages Encrypt with Party B’s Public Key Partner A Partner B Decrypt with Party B’s Private Key

19 Summary Questions 1. Name a few standard systems attacks Answer: 2. Distinguish between Denial-of-Service attack and Distributed Denial-of-Service attacks. Answer:

20 Summary Questions 3) Jason sends a message to Kristin using public key encryption. (a) What key will Jason use to encrypt the message? (b) What key will Kristin use to decrypt the message? (c) What key will Kristin use to encrypt the reply? (d) What key will Jason use to decrypt the reply? (e) Can the message and reply be long messages? Explain. (a) (b) (c) (d) (e) 4) Does public key encryption have a problem with secure key exchange for the public key? Explain.