Network Security Threats and Encryption Methods

1. Chapter 20:Network Security Business Data Communications, 4e

2. Security Threats • Passive attacks • Eavesdropping on, or monitoring, transmissions • Electronic mail, file transfers, and client/server exchanges are examples of transmissions that can be monitored • Active attacks • Modification of transmitted data • Attempts to gain unauthorized access to computer systems Business Data Communications, 4e

3. Encryption Methods • The essential technology underlying virtually all automated network and computer security applications is cryptography • Two fundamental approaches are in use: • conventional encryption, also known as symmetric encryption • public-key encryption, also known as asymmetric encryption Business Data Communications, 4e

4. Conventional Encryption • The only form of encryption prior to late 1970s • Five components to the algorithm • Plaintext: The original message or data • Encryption algorithm: Performs various substitutions and transformations on the plaintext. • Secret key: Input to the encryption algorithm. Substitutions and transformations performed depend on this key • Ciphertext: Scrambled message produced as output. depends on the plaintext and the secret key • Decryption algorithm: Encryption algorithm run in reverse. Uses ciphertext and the secret key to produce the original plaintext. Business Data Communications, 4e

5. Conventional Encryption Operation Business Data Communications, 4e

6. Conventional Encryption Requirements & Weaknesses • Requirements • A strong encryption algorithm • Secure process for sender & receiver to obtain secret keys • Methods of Attack • Cryptanalysis • Brute force Business Data Communications, 4e

7. Data Encryption Standard (DES) • Adopted in 1977, reaffirmed for 5 years in 1994, by NBS/NIST • Plaintext is 64 bits (or blocks of 64 bits), key is 56 bits • Plaintext goes through 16 iterations, each producing an intermediate value that is used in the next iteration. • DES is now too easy to crack to be a useful encryption method Business Data Communications, 4e

8. Triple DEA • Alternative to DES, uses multiple encryption with DES and multiple keys • With three distinct keys, TDEA has an effective key length of 168 bits, so is essentially immune to brute force attacks • Principal drawback of TDEA is that the algorithm is relatively sluggish in software Business Data Communications, 4e

9. Public-Key Encryption • Based on mathematical functions rather than on simple operations on bit patterns • Asymmetric, involving the use of two separate keys • Misconceptions about public key encryption • it is more secure from cryptanalysis • it is a general-purpose technique that has made conventional encryption obsolete Business Data Communications, 4e

10. Public-Key Encryption Components • Plaintext • Encryption algorithm • Public key • Private key • Ciphertext • Decryption algorithm Business Data Communications, 4e

11. Public-Key Encryption Operation Business Data Communications, 4e

12. Public-Key Signature Operation Business Data Communications, 4e

13. Characteristics of Public-Key • Infeasible to determine the decryption key given knowledge of the cryptographic algorithm and the encryption key. • Either of the two related keys can be used for encryption, with the other used for decryption. • Slow, but provides tremendous flexibility to perform a number of security-related functions • Most widely used algorithm is RSA Business Data Communications, 4e

14. Location of Encryption Devices • Link encryption • Each vulnerable communications link is equipped on both ends with an encryption device. • All traffic over all communications links is secured. • Vulnerable at each switch • End-to-end encryption • the encryption process is carried out at the two end systems. • Encrypted data are transmitted unaltered across the network to the destination, which shares a key with the source to decrypt the data • Packet headers cannot be secured Business Data Communications, 4e

15. Conventional EncryptionKey Distribution • Both parties must have the secret key • Key is changed frequently • Requires either manual delivery of keys, or a third-party encrypted channel • Most effective method is a Key Distribution Center (e.g. Kerberos) Business Data Communications, 4e

16. Public-Key EncryptionKey Distribution • Parties create a pair of keys; public key is broadly distributed, private key is not • To reduce computational overhead, the following process is then used: 1. Prepare a message. 2. Encrypt that message using conventional encryption with a one-time conventional session key. 3. Encrypt the session key using public-key encryption with recipient’s public key. 4. Attach the encrypted session key to the message and send it. Business Data Communications, 4e

17. Digital Signature Process Business Data Communications, 4e

18. Public Key Certificates 1. A public key is generated by the user and submitted to Agency X for certification. 2. X determines by some procedure, such as a face-to-face meeting, that this is authentically the user’s public key. 3. X appends a timestamp to the public key, generates the hash code of the result, and encrypts that result with X’s private key forming the signature. 4. The signature is attached to the public key. Business Data Communications, 4e

19. Web Vulnerabilities • Unauthorized alteration of data at the Web site • Unauthorized access to the underlying operating system at the Web server • Eavesdropping on messages passed between a Web server and a Web browser • Impersonation Business Data Communications, 4e

20. Methods for Improving Web Security • Securing the Web site itself • install all operating system security patches • install the Web server software with minimal system privileges • use a more secure platform • Securing the Web application Business Data Communications, 4e

21. Web Application Security • Secure HyperText Transfer Protocol (SHTTP) • Secure Sockets Layer (SSL) • Web server packages should incorporate both of these protocols Business Data Communications, 4e

22. Virtual Private Networks (VPNs) • The use of encryption and authentication in the lower protocol layers to provide a secure connection through an otherwise insecure network, typically the Internet. • Generally cheaper than real private networks using private lines but rely on having the same encryption and authentication system at both ends. • The encryption may be performed by firewall software or possibly by routers. Business Data Communications, 4e

23. IPSec • Can secure communications across a LAN, WANs, and/or the Internet • Examples of use: • Secure branch office connectivity over the Internet • Secure remote access over the Internet • Establishing extranet and intranet connectivity with partners • Enhancing electronic commerce security Business Data Communications, 4e

24. Benefits of IPSec • When implemented in a firewall or router, provides strong security for all traffic crossing the perimeter • IPSec in a firewall is resistant to bypass • Runs below the transport layer (TCP, UDP) and so is transparent to applications • Can be transparent to end users • Can provide security for individual users if needed Business Data Communications, 4e

25. IPSec Functions • IPSec provides three main facilities • authentication-only function referred to as Authentication Header (AH) • combined authentication/encryption function called Encapsulating Security Payload (ESP) • a key exchange function • For VPNs, both authentication and encryption are generally desired Business Data Communications, 4e

26. ESP Encryption & Authentication Business Data Communications, 4e

27. IPSec Key Management • Manual • System administrator manually configures each system with its own keys and with the keys of other communicating systems • Practical for small, relatively static environments • Automated • Enables the on-demand creation of keys for SAs and facilitates the use of keys in a large distributed system • Most flexible but requires more effort to configure and requires more software Business Data Communications, 4e