Outline

1. Advanced Research Issues In Security: Securing Key Internet TechnologiesCS 236On-Line MS ProgramNetworks and Systems Security Peter Reiher

2. Outline • Routing security • DNS security

3. Routing Security • Routing protocols control how packets flow through the Internet • If they aren’t protected, attackers can alter packet flows at their whim • Most routing protocols were not built with security in mind

4. Routing Protocol Security Threats • Threats to routing data secrecy • Usually not critical • Threats to routing protocol integrity • Very important, since tampering with routing integrity can be bad • Threats to routing protocol availability • Potential to disrupt Internet service

5. What Could Really Go Wrong? • Packets could be routed through an attacker • Packets could be dropped • Routing loops, blackhole routing, etc. • Some users’ service could be degraded • The Internet’s overall effectiveness could be degraded • Slow response to failures • Total overload of some links • Many types of defenses against other attacks presume correct routing

6. Where Does the Threat Occur? • At routers, mostly • Most routers are well-protected • But . . . • Several vulnerabilities have been found in routers • Also, should we always trust those running routers?

7. Different Types of Routing Protocols • Link state • Tell everyone the state of your links • Distance vector • Tell nodes how far away things are • Path vector • Tell nodes the complete path between various points • On demand protocols • Figure out routing once you know you two nodes need to communicate

8. Popular Routing Protocols • BGP • Path vector protocol used in core Internet routing • Arguably most important protocol to secure • RIP • Distance vector protocol for small networks • OSPF • ISIS • Ad hoc routing protocols

9. Fundamental Operations To Be Protected • One router tells another router something about routing • A path, a distance, contents of local routing table, etc. • A router updates its routing information • A router gathers information to decide on routing

10. Protecting BGP • BGP is probably the most important protocol to protect • Handles basic Internet routing • Works at autonomous system (AS) level • Rather than router level

11. BGP Issues • BGP is spoken (mostly) between routers in autonomous systems • On direct network links to their partner • Over TCP sessions that are established with known partners • Isn’t that enough to give reasonable security?

12. A Recent Counterexample • Pakistan became upset with YouTube over posting of “blasphemous” video • Responded by injecting a BGP update that sent all traffic to YouTube to a site in Pakistan • Which probably dropped it all • Rendered YouTube unavailable worldwide (well, 2/3s of world)

13. How Did This Happen? • Pakistan injected a BGP update advertising a path to YouTube • Which they had no right to do • It got automatically propagated by BGP • Everyone knows YouTube isn’t in Pakistan • But the routing protocol didn’t • Security required to prevent other future incidents

14. A Side Issues on This Story • Much thinking about Internet predicated on assumption that major players play by the rules • Pakistan didn’t • Not desirable to base Internet’s security on this assumption • Though sometimes not many other choices

15. C,B,A B,A A A D,C,B,A 1.2.3.* 1.2.3.* 1.2.3.* 1.2.3.* 1.2.3.* Basic BGP Security Issue A B C D E 1.2.3.* What do we need to protect? F G A wants to tell everyone how to get to 1.2.3.*

16. A D,F 1.2.3.* 1.2.3.* Well, What Could Go Wrong? A B C D E What if A doesn’t own 1.2.3.*? What if router D alters the path? F G What if router A isn’t authorized to advertise 1.2.3.*?

17. How Do We Solve These Problems? • Advertising routers must prove ownership and right to advertise • Paths must be signed by routers on them • Must avoid cut-and-paste attacks • And replay attacks

18. S-BGP • A protocol designed to solve most of the routing security issues for BGP • Intended to be workable with existing BGP protocol • Key idea is to tie updates to those who are allowed to make them • And to those who build them

19. Some S-BGP Constraints • Can’t change BGP protocol • Or packet format • Can’t have messages larger than max BGP size • Must be deployable in reasonable way

20. A 1.2.3.* An S-BGP Example A B C D E 1.2.3.* A can provide a certificate proving ownership F G How can B know that A should advertise 1.2.3.*?

21. D,C,B,A C,B,A B,A A 1.2.3.* 1.2.3.* 1.2.3.* 1.2.3.* Securing BGP Updates A B C D E 1.2.3.* What are these signatures actually attesting to? F G A wants to tell everyone how to get to 1.2.3.*

22. Who Needs To Prove What? • A needs to prove (to B-E) that he owns the prefix • B needs to prove (to C-E) that A wants the prefix path to go through B • C needs to prove (to D-E) the same • D needs to prove (to E) the same

23. So What Does A Sign? • A clearly must provide proof he owns the prefix • He also must prove he originated the update • And only A can prove that he intended the path to go through B • So he has to sign for all of that

24. Address Attestations in S-BGP • These are used to prove ownership of IP prefix spaces • IP prefix owner provides attestation that a particular AS can originate its BGP updates • That AS includes attestation in updates

25. Route Attestations • To prove that path for a prefix should go through an AS • The previous AS on the path makes this attestation • E.g., B attests that C is the next AS hop

26. How Are These Signatures Done? • Via public key cryptography • Certificates issued by proper authorities • ICANN at the top • Hierarchical below ICANN • Certificates not carried with updates • Otherwise, messages would be too big • Off-line delivery method proposed

27. S-BGP and IPSec • S-BGP generates the attestations itself • But it uses IPSec to deliver the BGP messages • Doing so prevents injections of replayed messages • Also helps with some TCP-based attacks • E.g., SYN floods

28. Protecting Other Styles of Protocols • Generally, how do you know you should believe another router? • About distance to some address space • About reachability to some address space • About other characteristics of a path • About what other nodes have told you

29. How Routing Protocols Pass Information • Some protocols pass full information • E.g., BGP • So they can pass signed information • Others pass summary information • E.g., RIP • They use other updates to create new summaries • How can we be sure they did so properly?

30. Who Are You Worried About? • Random attackers? • Generally solvable by encrypting/authenticating routing updates • Misbehaving insiders? • A much harder problem • They’re supposed to make decisions • How do you know they’re lying?

31. A Sample Problem 1 2 3 1 B C D E 0 A H 1.2.3.* 0 F G How can H tell someone lied? 1 2 Assume a distance vector protocol How can H tell that E lied?

32. Types of Attacks on Distance Vector Routing Protocols • Blackhole attacks • Claim short route to target • Claim longer distance • To avoid traffic going through you • Inject routing loops • Which cause traffic to be dropped • Inject lots of routing updates • Generally for denial of service

33. How To Secure a Distance Vector Protocol? • Can’t just sign the hop count • Not tied to the path • Instead, sign a length and a “second-to-last” router identity • By iterating, you can verify path length

34. An Example B C D E A H 1.2.3.* F G H needs to build a routing table entry for 1.2.3.* Should show hop count of 3 via G, 5 via E

35. One Way to Do It E D 2 1 E - B C D E A H C 3 D F G B 4 C A 5 B H directly verifies that it’s one hop to E Now we can trust it’s five hops to A H gets signed info that D is 2 hops through E Then we iterate

36. Who Does the Signing? • The destination • A in the example • It only signs the unchanging part • Not the hop count • But an update eventually reaches H that was signed by A

37. What About That Hop Count? • E could lie about the hop count • But he can’t lie that A is next to B • Nor that B next to C, nor C next to D, nor D next to E • Unless other nodes collude, E can’t claim to be closer to A than he is

38. What If Someone Lies? D E 2 1 E - B C D E A H C 3 D F G B 4 C A 5 B There’s limited scope for effective lies E can’t claim to be closer to A Since E can’t produce a routing update signed by A that substantiates that

39. A Difficulty • This approach relies on a PKI • H must be able to check the various signatures • Breaks down if someone doesn’t sign • That’s a hole in the network, from the verification point of view • Consider, in example, what happens if C doesn’t sign

40. What If C Doesn’t Sign? D E 2 1 - E B C D E A H C 3 D F G B 4 C A message coming through D tells us that it’s three hops to C A 5 B But how can he be sure D is next to C? But H can’t verify that Other than trusting D . . . H knows C is next to B And that B is next to A

41. What’s the Problem? E D 1 2 E - B C D E A H C 3 D F G B 4 C For this graph, no problem A 5 B But how about for this one? B C D E A H F G