1. Network Security Celia Li Computer Science and Engineering York University

2. Outline • Overview of network security and Cryptography • Authentication protocols • Wired networks • Wireless local area networks • Key management

3. Overview of Network Security • Confidentiality • The concealment of information or resources • Integrity • Data cannot be modified without being detected • Authenticity • A node can ensure the identity of the peer node it is communicating with. • Availability • The ability to use the information or resource desired

4. Overview of Network Security Security Attacks • An attack is any action that violates security • Common attacks • Eavesdropping • Integrity attack • Authenticity attack • Deny of service

5. Overview of Network Security • Eavesdropping – Message Interception • Unauthorized access to information • Packet sniffers and wiretappers • Illicit coping of data and programs

6. Overview of Network Security • Integrity Attack – Tampering with Message • Stop the flow of the message • Delay and optionally modify the message • Release the message again

7. Overview of Network Security • Authenticity Attack – Fabrication • Unauthorized assumption of other’s identity • Generate and distribute objects under this identity

8. Overview of Network Security • Attack on Availability • Destroy on Availability • Corrupt packets in transit • Denial of Service (DoS) • Crashing the server • Overwhelm the server (use up its resource)

9. Security Services • Access control • Only authorized actions (e.g., membership enrollment, data transmission) can be performed. • Authentication • Assurance that an entity of concern or the origin of a communication is authentic – it’s what it claims to be or from • Encryption • Converting data into a form that cannot be easily understood by unauthorized people

10. Security Services (cont.) • Key management • Generation, distribution and replace of keys • Secure routing • A message is eventually delivered to all legitimate nodes within a reasonable amount of time • Despite corrupting, dropping or misrouting the message.

11. Overview of Cryptography • Why cryptography? • Used to hide information • Network information needs to be communicated through insecure channel • Stored information may be accessed without proper authorization • What cryptography can do? • Encryption algorithms: only the authorized party can understand the encrypted message • Digital signature: allow people to verify the authenticity of the message

12. Overview of Cryptography • Encryption Algorithms • Scrambling of message such that only intended receiver can unscramble them • Encrypting function- produces encrypted message • Decrypting function- extracts original message • Key - parameter that controls encryption/decryption

13. Overview of Cryptography • What is Key? • A piece of information that controls the operation of an encryption algorithm. • A key specifies the particular transformation of plaintext into ciphertext, or vice versa during decryption. • To prevent a key from being guessed, keys need to be generated truly randomly

14. Overview of Cryptography • Symmetric Encryption Process • Use the same key for both encryption and decryption • Example: DES, 3DES

15. Overview of Cryptography • Public Key Encryption Process • Use a pair of keys, public key and private key • finding out the private key is extremely difficult, even if the public key is known • Example: RSA, Elliptic Curve

16. Overview of Cryptography • Example

17. Overview of Cryptography • Symmetric & Public Key Encryption • Symmetric encryption is fast but not as safe as public key encryption. But because of its speed, it's commonly used for multimedia, e-commerce transactions. • Public key encryption is more complex--and more secure. More computation is required, so the process takes longer

18. Overview of Cryptography • Hash Function • A reproducible method of turning data into a small number that may serve as a digital "fingerprint" of the data (Message Digest) • If two hashes are different, then the two inputs are different in some way. • If a hash value is calculated for a piece of data, and then one bit of that data is changed, a hash function produces a completely different hash value. • Unidirectional (cannot calculate text from hash)

19. Overview of Cryptography • Hash Function • Two most-commonly used hash functions: MD5 and SHA-1

20. Overview of Cryptography • Hash Function for Date Integrity • If the two hashes do not match, the message was altered

21. Overview of Cryptography • Digital Signature • A number attached to a message, when other people receive the message, he can simply verify the attached number to confirm whether the message has been changed or not. • Gives a recipient reason to believe that the message was created by a known sender. • Commonly used for software distribution, financial transactions, and in other cases where it is important to provide authenticity and integrity.

22. Overview of Cryptography • Digital Signature Generating Process • Hash a document

23. Overview of Cryptography • Digital Signature Generating Process • Sign the message digest

24. Overview of Cryptography • Digital Signature Verifying Process

25. Overview of Cryptography • Digital Signature Verifying Process

26. Overview of Cryptography • Digital Signature Algorithms • The Digital Signature Algorithm (DSA) • The RSA digital signature algorithm • The Elliptic Curve Digital Signature Algorithm (ECDSA)

27. Our Focus • Authentication • Key management