1. A New Approach to DNS Security (DNSSEC)
Author:
Giuseppe Ateniese
Stefan Mangard
Presenter: Liu, Xiaotao

2. Outline Overview of DNS Motivation PK-DNSSEC SK-DNSSEC
Comparison with PK-DNSSEC
Usage of DNSSEC

3. Outline Overview of DNS Motivation PK-DNSSEC SK-DNSSEC
Comparison with PK-DNSSEC
Usage of DNSSEC

4. What is the DNS Domain Name System
Distributed ‘database’ to resolve domain names
Labels translate to Resource Records
Address (A)
Mail hosts (MX)
Text (TXT)
and much more….
Resource records stored in zones
Highly scalable

5. A DNS tree . root domain top level .net .com .money.net .kids.net
.os.net
zone
mac.os.net
nt.os.net
corp.money.net
unix.os.net
dop.kids.net
marnick.kids.net

6. DNS data Example Zone file
dacht.net 7200 IN SOA ns.ripe.net. olaf.ripe.net.(
; Serial
; Refresh 12 hours
; Retry 4 hours
; Expire 4 days
7200 ; Negative cache 2 hours )
dacht.net IN NS ns.ripe.net.
dacht.net IN NS ns.high5.net.
pinkje.dacht.net IN A
host25.dacht.net IN A
Label
ttl
class
type
rdata

7. Common Resource Records
RECORD TYPE
DESCRIPTION
USAGE A
An address record
Maps FQDN into an IP address
PTR
A pointer record
Maps an IP address into FQDN NS
A name server record
Denotes a name server for a zone
SOA
A Start of Authority record
Specifies many attributes concerning the zone, such as the name of the domain (forward or inverse), administrative contact, the serial number of the zone, refresh interval, retry interval, etc.
CNAME
A canonical name record
Defines an alias name and maps it to the absolute (canonical) name MX
A Mail Exchanger record
Used to redirect for a given domain or host to another host

8. DNS resolving Question: www.cnn.com . resolver stub resolver .com
A ?
dns.cs.umass.edu
lab.cs.umass.edu
resolver
ask .com server
the ip address of .com server
stub
resolver
A ?
xxx.xxx.xxx.xxx
A ?
.com
ask cnn.com server
the ip address of cnn.com server
add to cache
A ?
xxx.xxx.xxx.xxx
cnn.com

9. DNS Data flow Zone file master resolver slaves Dynamic updates
Zone administrator
Zone file
master
resolver
slaves
Dynamic
updates
stub resolver

10. Outline Overview of DNS Motivation PK-DNSSEC SK-DNSSEC
Comparison with PK-DNSSEC
Usage of DNSSEC

11. DNS Vulnerabilities master resolver Zone file Dynamic updates slaves
Cache impersonation
Corrupting data
Impersonating master
Zone
administrator
master
resolver
Zone file
Dynamic
updates
slaves
stub resolver
Cache pollution by
Data spoofing
Unauthorized updates
Data
Protection
Server Protection

12. Why DNSSEC DNSSEC protects against data spoofing and corruption
DNSSEC also provides mechanisms to authenticate servers and requests
DNSSEC provides mechanisms to establish authenticity and integrity

13. Outline Overview of DNS Motivation PK-DNSSEC SK-DNSSEC
Comparison with PK-DNSSEC
Usage of DNSSEC

14. PK-DNSSEC (Public Key)
The DNS servers sign (digitally encrypt)the hash of resource record set with its private keys
Resouce record set: The set of resource records of the same type.
Public KEYs can be used to verify the SIGs
The authenticity of public KEYs is established by a SIGnature over the keys with the parent’s private key
In the ideal case, only one public KEY needs to be distributed off-band (the root’s public KEY)

15. DNSSEC new RRs 2 Public key related RRs
SIG signature over RRset made using private key
KEY public key, needed for verifying a SIG over a RRset, signed by the parent’s private key
One RR for internal consistency (authenticated denial of data)
NXT RR to indicate which RRset is the next one in the zone
For non DNSSEC public keys: CERT
RFC 2535 discusses these RRs in detail.
CERT RR is outside the scope of this course.

16. SIG RRs
Cover each resource record set with a public-key signature which is stored as a resource record called SIG RR
SIG RRs are computed for every RRset in a zone file and stored
Add the corresponding pre-calculated signature for each RRset in answers to queries
Must include the entire RRset in an answer, otherwise the resolver could not verify the signature

17. SIG(0)
Use public-key signature to sign the whole message each time the server responses the queries
Provide integrity protection and authentication of the whole message
Can be scaled to provide authentication of query requests
Not be practical to use on a large scale environment

18. Compare SIG RRs with SIG(0)
More computation on DNS server caused by SIG(0)
More network traffic caused by SIG RRs
More storage need by SIG RRs

19. Verifying the tree Question: www.cnn.com . (root) stub resolver
A ?
dns.cs.umass.edu
lab.cs.umass.edu
resolver
ask .com server
SIG(the ip address and PK of .com server)
by its private key
stub
resolver
A ?
xxx.xxx.xxx.xxx
A ?
.com
transaction
signatures
ask cnn.com server
SIG(the ip address and PK of cnn.com server)
by its private key
add to cache
slave servers
A ?
SIG(xxx.xxx.xxx.xxx)
by its private key
transaction
signatures
cnn.com

20. Verifying Verify a SIG over data using the public KEY
DNS data is signed with the private key
Verify the SIG with the KEY mentioned in the SIG record
The key can be found in the DNS or can be locally configured

21. Outline Overview of DNS Motivation PK-DNSSEC SK-DNSSEC
Comparison with PK-DNSSEC
Usage of DNSSEC

22. SK-DNSSEC (Symmetric Certificates)
The usage of symmetric ciphers through AES or Blowfish in CBC mode.
The usage of symmetric signatures via MAC functions.
Combine encryption techniques with MAC functions as Ek(m, MACl(m)).
Each message contains a nonce to avoid replay attack. A nonce is pair of a random number and a timestamp.

23. SK-DNSSEC (cont.)
Given the DNS tree of domains, each node shares a key with its parent, called master key
The root domain has an asymmetric key pair(public and private key) as well as its own master key that is not shared with any others
The resolvers must have an authentic copy of root’s public key

24. Notation

25. DNS Root Certificate

26. DNS Request to Root
Info(Pxy) has to minimally contain the identity strings Ix and Iy. Inception and
expiration dates, details about the encryption and authentication algorithms
employed, certificate and key unique identifiers, and the identity of the creator of
the certificate

27. DNS Request to Intermediate Server

28. DNS Request to Authoritative Server

29. For mutual authentication
For any 0  i  n

30. The problem of PK and SK DNSSEC
In SK-DNSSEC, the root servers need to decrypt the message encrypted by the public key
In PK-DNSSEC, the potential increase of network traffic due to larger DNS messages
In PK-DNSSEC, the high cost of verifying the public-key digital signatures at the resolvers side

31. Hybrid Approach The root servers use PK-DNSSEC
The top-level domains use SK-DNSSEC

32. Outline Overview of DNS Motivation PK-DNSSEC SK-DNSSEC
Comparison with PK-DNSSEC
Usage of DNSSEC

33. Efficiency
PK-DNSSEC with SIG RR. For each RRset in the answer, a pre-calculated SIG RR is included
PK-DNSSEC with SIG(0). DNS messages do not contain SIG RRs, but are rather signed as a whole by SIG(0)-type signature.
SK-DNSSEC. DNS messages are secured by symmetric signatures and encryption.

34. Performance
(800M HZ)

35. Performance (cont.)

36. Network Traffic

37. Storage

38. Outline Overview of DNS Motivation PK-DNSSEC SK-DNSSEC
Comparison with PK-DNSSEC
Usage of DNSSEC

39. Public-key Distribution System
Global real time availability
Easy access to DNS
Scalability
Hierarchical organization
Globally unique names
Globally unique host name
Cryptographic binding of name and key
KEY RR binds DNS names with keys

40. Q&A
Thank You!