IPSec (Security at the IP Layer)

1. This presentation will probably involve audience discussion, which will create action items. Use PowerPoint to keep track of these action items during your presentation • In Slide Show, click on the right mouse button • Select “Meeting Minder” • Select the “Action Items” tab • Type in action items as they come up • Click OK to dismiss this box • This will automatically create an Action Item slide at the end of your presentation with your points entered. IPSec (Security at the IP Layer) Security Objectives and issues associated with IPSEC Overview of Network-Layer IP security Cryptographic checksums for message integrity protection IPSEC encryption and authentication headers from Chapter 5 – Internet Cryptography Choi yiu kuen

2. Security Review IPsec - Internet Protocol security Link secuirty - in line encryptor Choi yiu kuen

3. Security in Layer 3 • Security at the IP layer, called IPSEC, is a set of general purpose protocols for Protecting the TCP/IP communications in the Internet. • It is the third layer (layer 3). • It is used to protect traffic between host not user. Choi yiu kuen

4. Difference between IPSec and link security Internet IPSec in-line encryptor in-line encryptor leased line Link Security Choi yiu kuen

5. Security Objectives – Reasons (1) • Protect traffic between trusted hosts from forgery or eavesdropping. It is because traffic between end pairs over the Internet might pass through hostile hosts. Attackers could do damage. • Protect the whole range of Internet software currently in use. The services include such as e-mail, HTTP, Remote access that relies on TCP/IP must be protected. (too expensive to replace it.) Choi yiu kuen

6. Example of protecting traffic untrusted area Choi yiu kuen

7. Security Objectives – Reasons (2) • An untrusted network is in place. In many cases, the untrusted network is the public Internet and is too expensive to replace by an a trusted network between two end pairs (use leased line). • Protection is automatic. Individual users do not need to modify the protocol. Internet Public Network Untrusted Choi yiu kuen

8. Security Issues (1) • Security must be independent of and transparent to existing ISP (internet service provider). The issue is that people wants to connect safely with other trusted sites using existing ISPs to carry packets. • Crypto applied at the network level (level 3) leaves more plaintext in the packets. Network layer will leave even more address information in the plaintext. Choi yiu kuen

9. Security Issues (2) • Site security yields per-site authentication: Network level security measures can distinguish between traffic from approved sites and other sites, but it can’t reliably distinguish between traffic from individual users at an approved site. This yields virtual private networks. • Numerous factors have produced uncertainty in key management: Developers, vendors and technologies have produced competing alternatives for IPSEC key management. Choi yiu kuen

10. Security Technology: Cryptographic Checksums • Cryptographical checksum detects changes in a protected message. • Unlike encryption, it will not apply to the data, but to seal the message against changes. • For example, Alice is ending a data $123 to Bob. The system should detect that the checksum of $123 and find that it is 412 (an example, not actual value). Alice will send a message containing $123 + encrypted value of 412 (say t&6). Bob will receive the message $123 and he will then re-compute the checksum and use the same key to encrypt to see whether it produces t&6. If they are equal, it means that there is no change. Choi yiu kuen

11. Example – message consists of data and Crypto checksum Choi yiu kuen

12. Example – the message has been modified Choi yiu kuen

13. Modifying a Message protected with a cryptographic checksum • What happens if the hacker modifies the data such that the plaintext checksum is the same. Choi yiu kuen

14. Solution – Use on-way hash • One-way hash functions are checksumlike functions, but are explicitly designed so that an attacker cannot construct a forged message (false message) that yields the same result. • Like previous page, the hacker understands that $123 and $654 will produce the same plaintext checksum. Choi yiu kuen

15. How one-way hash works • Like checksums, one way hash functions take an arbitrarily long data sequence and compute a check value of a fixed size called the hash value. • One-way hash functions try to generate a fingerprint of data. • The function is sensitive to any change in the data. Very difficult to determine the fingerprint Choi yiu kuen

16. Protect message data with a keyed hash Choi yiu kuen

17. Description of one-way hash • The data being sent combines the secret key. • The sender appends a secret key to the message contents and compute a one-way hash. • The sender then sends the message data plus the hash. • The recipient uses the same key to re-compute and validate the hashed value. Choi yiu kuen

18. Why the hacker cannot reproduce – one way hash • Hacker cannot generate the right checksum value for a given message unless they have a copy of the secret key being used. • The correct hash value depends on constructing the same input data,which includes both the data sent and the secret key. • Attackers cannot construct a similar beneficial message that yields the same hash value. Choi yiu kuen

19. IPSEC: IP Security Protocol • The existing IP protocol is version 4. (32 bit for IP address) • IPSEC is an extension to the existing IP networking protocol. • IPSEC evolved as part of the development of the new IP version 6. • IPSEC is designed to provide privacy, forgery detection or both for IP packets. Choi yiu kuen

20. IPSEC is transparent to Internet Applications • IPSEC protections are applied to above the IP routing information and below the application data. Choi yiu kuen

21. Packet header (no need to memorise) • Authentication header: It provides integrity-checking information. We can then detect if the packet’s contents has been modified while traveling across untrusted networks. • Encapsulating security payload: The ESP encrypts the data contents of the remainder of the packet so that the contents cannot be extracted while traveling across untrusted networks. Choi yiu kuen

22. Security Associations in IPSEC (1) • In order to communicate, each pair hosts using IPSEC must establish a security association with one another. • It will cover what types of protection to apply, how to do encryption or authentication and which keys need to be used. Choi yiu kuen

23. Security Associations in IPSEC (2) • IPSEC must maintain the following information: • Specification of the Crypto methods to be used by that SPI • Keys to be used by the Crypto methods when processing traffic for that SPI • The hosts or other entities associated with this traffic. Choi yiu kuen

24. Replay Attacks • The TCP/IP protocols are not explicitly designed to identify and reject packets that are cleverly collected and replayed. • TCP/IP protocols are designed to operate correctly even if data packets are transmitted. • There is no replay protection. • It does not mean that replay attack is not a risk. It is difficult to differentiate the duplicated packet or malicious (malicious means hostile) replay. Choi yiu kuen

25. No need to memorise IPSEC Authentication • IPSEC Header is a header in an IP packet that contains cryptographical checksum. • The first word (32 bits) identifies the type and location of the next protocol • The next 32 bits are SPI tells the destination host which security association applies to this header. Choi yiu kuen

26. Header Format Choi yiu kuen

27. IPSEC Encryption • IPSEC ESP also defines a header in the IP Header. • ESP processing also includes transforming the protected data into an unreadable, encrypted form. • ESP header simply contains SPI for the destination host’s security association. Choi yiu kuen

28. Format and contents of the IPSEC ESP • The ESP consists of 32-bit SPI field, followed by data with a format that is related to the encryption procedure. Choi yiu kuen

29. IPSEC Key Management • The success of IPSEC depends on the relationship between • Authorised entity • Crypto keys • Identification codes within its message • One of the major areas is the Key. Choi yiu kuen

30. IPSEC Key Management There are four types: • Manual Keying • Simple Key Interchange Protocol • Inter Security Association and Key Management Protocol • Photuris No need to memorise all, Understand one of them Choi yiu kuen

31. Manual Keying • Provide a way to configure security associations manually • Specifying SPIs, Crypto Methods and Keys as well as identifying which host • The crypto material has to be distributed MANUALLY once the keys are exchanged. Choi yiu kuen

32. SKIP • SKIP negotiations and exchanges session keys between IPSEC hosts using a special header in each IP packet. • Key exchange is based on a shred secret like X.917 (not need to memorise) • The design makes it easy to integrate with the IPSEC software. • SUN Microsystems developed SKIP and used it in their products. Choi yiu kuen

33. ISAKMP • It is a broad and general-purpose protocol. • It is intended both to manage security associations and to handle key exchange. • It is based on IPSEC committee of the Internet Engineering Task Force (IETF) Choi yiu kuen

34. Other Security Protocols • IPSO: IP Security OPTION • SNDS:Secure Data Network System • NLSP: Network Layer Security Protocol • SSL: Secure Sockets Layer * • PPTP: Point to point Tunneling Protocol Choi yiu kuen

35. Summary • IPSEC provides Crypto protection to TCP/IP between hosts at the network layer • IPSEC Uses: Cryptographic Checksums to ensure the data is not modified. • For example: It uses one way hash • But it cannot prevent replay attacks (fixed by sequence number) • IPSEC Authentication and IPSEC Encryption • IPSEC Key management: 4 methods • Other Security protocol:SSL (next chapter) Choi yiu kuen

36. Next week Security Protocol at Transport layer Choi yiu kuen