1. DNS Security

2. Fundamental Problems of Network Security
Internet was designed without security in mind
Initial design focused more on how to make it work, than on how to prevent abuses
Initial environment mostly consisted of research institutions---assumption on the benign behaviors of users
Fundamental security problem of current network technology:
Has no way of telling whether the resource is located “correctly,” or the information is transferred “correctly”
Has no data authentication and confidentiality protection

3. Example Security Problems by Incorrect Resource Location
DNS poisoning
BGP routing vulnerabilities
ARP poisoning
ARP (Address Resolution Protocol) is used to query for the MAC address associated with an IP address
Any device attached physically to a subnet can claim to be the “owner” of the IP
IP Spoofing
Routers typically do not check source IP addresses
A packet can claim to be coming from any IP address
Routers have no good way to check IP addresses either

4. The Domain Name System Basic Internet Database
Maps names to IP addresses
Also stores IPv6 addresses, mail servers, service locators, Enum (phone numbers), etc.
Data organized as tree structure.
Each zone is the authority for its local data.
Root
edu
com uk
usf
cisco
ibm co
www
Adapted from slides of Prof. Dan Massey at Colorado State University

5. Domain Name Service Provides binding between URL and IP address
Both forward and reverse mapping
Divide URL space into zones; Each name server handles mapping in its zone
DNS Resource Record (RR)
Can be viewed as tuples of the form
<name, TTL, class, type, data>
types: A (IP address)
MX (mail servers)
NS (name servers)
PTR (reverse look up)

6. DNS Protocol ISP What is the IP address of www.usf.edu? root Server
Go ask
What is the IP address of
ISP
NS Server for edu ( )
What is the IP address of
Go ask
What is the IP address of
ISP’s DNS Resolver
NS Server for usf.edu ( )

7. Example Response from the .edu NS server Delegation of authority
;; QUESTION SECTION:
; IN A
;; AUTHORITY SECTION:
usf.edu IN NS mother.usf.edu.
usf.edu IN NS ziggy.usf.edu.
usf.edu IN NS clemson-ns1.usf.edu.
;; ADDITIONAL SECTION:
mother.usf.edu IN A
ziggy.usf.edu IN A
clemson-ns1.usf.edu IN A …
Glue records

8. DNS Security Problems
A DNS resolver has no way to determine if the response of a query does come from the legitimate server
It will accept a response if
The port number matches the source port of the request
Has the correct Transaction ID (TXID).
It will accept all RR’s that are in the queried server’s bailiwick
The bailiwick is the domain in which the server has authority according to the referral path

9. Classical DNS Poisoning
DoS flooding
DNS queries
ISP
faked responses
What is the IP address of
What is the IP address of
recursive query
Recursive DNS resolver
NS Server for usf.edu

10. Conditions for classical DNS poisoning attacks
Must guess right the correct source-port number
Must guess right the correct TXID (16 bits)
The fake response must arrive before the legitimate response
If any of the above fails, the attack fails and there will be no chance to attack again until the TTL expires

11. Kaminsky Attack (2008)
What is the IP address of foo.usf.edu?
usf.edu NS A
ISP
What is the IP address of foo.usf.edu?
No such url
Recursive DNS resolver
NS Server for usf.edu

12. Implication of Kaminsky Attack
Dramatically reduces the complexity and increases the effectiveness of DNS cache poisoning
No longer needs to wait for TTL to expire
The attacker can control when and what queries are issued
A complete domain may be hijacked
Even TLD’s are vulnerable
Only needs 10 secs to succeed

13. Short-term mitigation
Increase the brute-force search space
16 bits TXID is too small and can be easily brute-forced
Randomize source port number
Use other entropy in DNS messages
e.g. Letter cases in URL

14. Long-term Solution: DNSSEC
Use public-key signature to authenticate DNS messages
Domain names already form a hierarchy
Parent signs children’s public keys
Resolver only needs to know the root public key to authenticate DNS messages

15. The Domain Name System Basic Internet Database
Maps names to IP addresses
Also stores IPv6 addresses, mail servers, service locators, Enum (phone numbers), etc.
Data organized as tree structure.
Each zone is the authority for its local data.
Root
edu
com uk
usf
cisco
ibm co
www
Adapted from slides of Prof. Dan Massey at Colorado State University

16. DNSSEC Provides a “natural” PKI Keys organized as tree structure.
Maps zones to their keys
Parent-zone sign child zones’ keys
Keys organized as tree structure.
Each zone is the authority for its local data.
A zone’s key is only effective in its zone
Root
edu
com uk
usf
cisco
ibm co
www
Adapted from slides of Prof. Dan Massey at Colorado State University

17. DNS RR Review DNS Resource Record (RR)
Can be viewed as tuples of the form
<name, TTL, class, type, data>
types: A (IP address)
MX (mail servers)
NS (name servers)
PTR (reverse look up) RRSIG (signature)
DNSKEY(public key) …

18. DNSSEC Records Introduce a new data type: RRSIG
name TTL class type value
{ IN A }
name TTL class type covered_type
{ IN RRSIG A …
… usf.edu.
Base 64 encoding of signature}
not after
not before
key name

19. DNSSEC Records Introduce a new data type: DNSKEY
name TTL class type value
{ usf.edu IN DNSKEY Base 64 encoding
of public key}
name TTL class type covered_type
{ usf.edu IN RRSIG DNSKEY …
… edu.
Base 64 encoding of signature}
not after
not before
key name

20. Authenticated Non-existence
What if the usf.edu server is asked the IP address of a non-existent url (e.g. foo.usf.edu)?
Can’t sign non-existence on the fly because the server does not have the private key (why?)
NSEC record
“The url after eng.usf.edu is health.usf.edu”
Order all the url’s in a zone and sign all the NSEC records ahead of time
Problem: enables zone enumeration
NSEC3 addresses this concern by using hashes of zone names instead of zone names themselves

21. Key Management PKedu PKusf PKusf2 PKusf2 Sig{PKusf }PKedu PKsigning
DS Record
NS for .edu
Want to change PKusf to PKusf2
PKusf
PKusf2
PKusf2
sign
Sig{PKusf }PKedu
PKsigning
Do not need to notify parent if changed
NS for usf.edu …

22. Potential Usage of DNSSEC
If successfully deployed, DNSSEC can serve as a universal PKI
Sign public keys for web sites
Sign public keys for addresses

23. SSL/TLS I am Alice I am Bob, inc PKB is Bob’s public key PKB
E(PKB , s)
{m}KC || MACKM(m)
Alice
Bob
KC, KM = h(s)

24. DNS-based Authentication of Named Entities (DANE)
Use DNSSEC to sign certain statements (DANE records)
The currently proposed DANE records address trust of TLS certificates
TLSA DANE records
Yet another type of DNS resource record (RR)
Three types of statements
CA Constraints
Service Certificate Constraints
Trust Anchor Assertion
CA Constraints: The client should only accept certificates issued under a specific CA.
Service Certificate Constraints: The client should only accept a specific certificate.
Trust Anchor Assertion: The client should use a domain-provided trust anchor to validate certificates for that domain.

25. Advantages of DANE compared with X.509
Real delegation of power
Better accountability
More flexibility
Better damage control
Clearer semantics
DANE records only means that “this domain’s owner says…”

26. Problems of DNSSEC Key revocation
If a zone’s private key is compromised, the damage continues even after the key is replaced, until the parent’s cert on the key expires
Certificate revocation?
All the revocation problems with digital signatures will apply
Issue short-term certificates instead?
Then the upper-level zones will have to be more involved in maintaining the DNSSEC structure
Against the initial design principles of DNS: autonomy of individual zones

27. Deployment Status Has been on-going for a number of years
Check
Root domain signed July, 2010
DNSSEC now deployed at key zones including net, com, gov, and edu.
“Almost” ready to use at the resolver level