1. Advanced Research Issues In Security: Securing Key Internet Technologies CS 236 On-Line MS Program Networks 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. Basic BGP Security Issue
1.2.3.* A
1.2.3.*
B,A
1.2.3.*
C,B,A
1.2.3.*
D,C,B,A A B C D E
1.2.3.* A
1.2.3.*
What do we need to protect? F G
A wants to tell everyone how to get to *

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

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

21. What are these signatures actually attesting to?
Securing BGP Updates
1.2.3.* A
1.2.3.*
B,A
1.2.3.*
C,B,A
1.2.3.*
D,C,B,A 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 *

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 A H F G How can H tell someone lied?A H
1.2.3.* 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 *
Should show hop count of 3 via G, 5 via E

35. One Way to Do It H directly verifies that it’s one hop to E1 - B C D E D 2 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? There’s limited scope for effective lies1 - B C D E D 2 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? E 1 - B C D E D 2 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? For this graph, no problem1 - B C D E D 2 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? A B C D E F G H