1. Securing the Internet CS 239 Advanced Topics in Computer Security Peter Reiher November 23, 2010

2. The Issue We all depend on the Internet
Its very fundamentals aren’t well secured
What are the problems?
What are the solutions?

3. What We Aren’t Talking About
Confidentiality and integrity
Use end-to-end encryption
Maybe other technologies for privacy
Security of end hosts
Attacks merely perpetrated across the network
Denial of service attacks

4. What’s That Leave? Core services required for the Internet to operate
Routing
Name translation
QoS security, multicasting, and other services arguably in scope
But not widely used

5. 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

6. 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

7. 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

8. 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?

9. A Recent Counterexample
China recently hijacked about 1/16 of all Internet routes
Probably more of the traffic
For around 15 minutes
Included traffic that should have been purely internal to the US
Not clear if it was accidental
Not clear if it will happen again

10. How Did This Happen?
China injected a BGP update advertising a good path to large chunks of the Internet
Which they had no right to do
And didn’t actually have
It got automatically propagated by BGP
The routes weren’t plausible
But the routing protocol doesn’t understand plausibility

11. 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 *

12. 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 *?

13. 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

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

15. 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

16. 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 *

17. 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

18. 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

19. S-BGP and Public Key Crypto
Signatures done via PK
Requires PK infrastructure
Agreed upon by all parties in the Internet
No such agreement available, right now

20. Another Approach to Securing BGP Updates
Pretty Good BGP
Routers keep track of recent routes to destinations
Accept updates that are on the list
Maybe don’t accept those that aren’t
Doesn’t solve all problems
But no crypto or PK infrastructure

21. DNS Security
The Domain Name Service (DNS) translates human-readable names to IP addresses
Threats to name lookup secrecy
Definition of DNS system says this data isn’t secret
Threats to DNS information integrity
Very important, since everything trusts that this translation is correct
Threats to DNS availability
Potential to disrupt Internet service

22. The DNS Lookup Process
lookup thesiger.cs.ucla.edu
answer
ping thesiger.cs.ucla.edu
If the answer is wrong, in standard DNS the client is screwed
Should result in a ping packet being sent to

23. Doing Hierarchical Translation
DNS root server
Where’s edu?
lookup thesiger.cs.ucla.edu
edu root server
Where’s ucla.edu?
Where’s cs.ucla.edu?
Where’s thesiger.cs.ucla.edu?
ucla.edu root server
cs.ucla.edu root server

24. Where Can This Go Wrong?
Someone can spoof the answer from a DNS server
Relatively easy, since UDP is used
One of the DNS servers can lie
Someone can corrupt the database of one of the DNS servers

25. lookup thesiger.cs.ucla.edu
The Spoofing Problem
lookup thesiger.cs.ucla.edu
answer
Unfortunately, most DNS stub resolvers will take the first answer
answer

26. lookup thesiger.cs.ucla.edu
DNS Servers Lying
answer
lookup thesiger.cs.ucla.edu
. . .
thesiger.cs.ucla.edu
That wasn’t very nice of him!

27. DNS Database Corruption
answer
lookup thesiger.cs.ucla.edu
. . .
thesiger.cs.ucla.edu

28. The DNSSEC Solution Sign the translations Who does the signing?
The server doing the response?
Or the server that “owns” the namespace in question?
DNSSEC uses the latter solution

29. Implications of the DNSSEC Solution
DNS databases must store signatures of resource records
There must be a way of checking the signatures
The protocol must allow signatures to be returned

30. The DNSSEC Signing Hierarchy
In principle, ICANN signs for itself and for top level domains (TLDs)
Like .com, .edu, country codes, etc.
Each TLD signs for domains under it
Those domains sign for domains below them
And so on down

31. An Example
Who signs the translation for thesiger.cs.ucla.edu to ?
The UCLA CS DNS server
How does someone know that’s the right server to sign?
Because the UCLA server says so
Securely, with signatures
The edu server verifies the UCLA server’s signature
Ultimately, hierarchical signatures leading up to ICANN’s attestation of who controls the edu namespace
Where do you keep that information?
In DNS databases

32. Status of DNSSEC Working implementations available
In use in some places
Heavily promoted
First by DARPA
Now by DHS
But not really successful
That may be changing
.gov is signed, as of 2010
ICANN signed root in July 2010

33. Issues For Discussion
Are there other Internet-level security problems?
What approaches to securing the Internet itself are realistic?
Worth worrying about, or learn to live with it?