A New Approach to DNS Security (DNSSEC)

Author:Giuseppe Ateniese

Stefan Mangard

Presenter: Liu, Xiaotao

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

Outline• Overview of DNS• MotivationMotivation• PK-DNSSECPK-DNSSEC• SK-DNSSECSK-DNSSEC• Comparison with PK-DNSSECComparison with PK-DNSSEC• Usage of DNSSECUsage of DNSSEC

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

domain

zone

A DNS tree

.money.net .kids.net

corp.money.net

unix.os.netmac.os.net

nt.os.net

.os.net

.net .com

marnick.kids.netdop.kids.net

. root

top level

DNS data

Label ttl class type rdata

Example Zone file dacht.net 7200 IN SOA ns.ripe.net. olaf.ripe.net.( 2001061501 ; Serial 43200 ; Refresh 12 hours 14400 ; Retry 4 hours 345600 ; Expire 4 days 7200 ; Negative cache 2 hours )dacht.net 7200 IN NS ns.ripe.net.dacht.net 7200 IN NS ns.high5.net.pinkje.dacht.net 3600 IN A 193.0.1.162host25.dacht.net 2600 IN A 193.0.3.25

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 email for a given domain or host to another host

DNS resolving

stub resolver

Question: www.cnn.com

www.cnn.com A ?

resolver

. www.cnn.com A ?

ask .com server the ip address of .com server

.comwww.cnn.com A ?

ask cnn.com serverthe ip address of cnn.com server

cnn.com

www.cnn.com A ?

xxx.xxx.xxx.xxx

xxx.xxx.xxx.xxx

add to cache

www.cnn.com

lab.cs.umass.edudns.cs.umass.edu

DNS Data flow

master resolver

stub resolver

Zone administrator

Zone file

slavesDynamicupdates

Outline• Overview of DNSOverview of DNS• Motivation• PK-DNSSECPK-DNSSEC• SK-DNSSECSK-DNSSEC• Comparison with PK-DNSSECComparison with PK-DNSSEC• Usage of DNSSECUsage of DNSSEC

Data

ProtectionServer Protection

DNS Vulnerabilities

Zone file

slaves

master resolver

stub resolver

Zone administrator

Dynamicupdates

Cache pollution byData spoofingUnauthorized updates

Corrupting data Impersonating master

Cache impersonation

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

Outline• Overview of DNSOverview of DNS• MotivationMotivation• PK-DNSSEC• SK-DNSSECSK-DNSSEC• Comparison with PK-DNSSECComparison with PK-DNSSEC• Usage of DNSSECUsage of DNSSEC

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)

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

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

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

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

Verifying the tree

stub resolver

Question: www.cnn.com

www.cnn.com A ?

resolver

. (root)www.cnn.com A ?

ask .com server SIG(the ip address and PK of .com

server) by its private key

.comwww.cnn.com A ?

ask cnn.com serverSIG(the ip address and PK of cnn.com server)

by its private key

cnn.com

www.cnn.com A ?

SIG(xxx.xxx.xxx.xxx)by its private key

xxx.xxx.xxx.xxx

add to cache

www.cnn.com

lab.cs.umass.edudns.cs.umass.edu

transaction signatures

slave serverstransaction signatures

• 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

Verifying

Outline• Overview of DNSOverview of DNS• MotivationMotivation• PK-DNSSECPK-DNSSEC• SK-DNSSEC• Comparison with PK-DNSSECComparison with PK-DNSSEC• Usage of DNSSECUsage of DNSSEC

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.

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

Notation

DNS Root Certificate

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 algorithmsemployed, certificate and key unique identifiers, and the identity of the creator ofthe certificate

DNS Request to Intermediate Server

DNS Request to Authoritative Server

For mutual authenticationFor any 0 i n

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

Hybrid Approach

• The root servers use PK-DNSSEC

• The top-level domains use SK-DNSSEC

Outline• Overview of DNSOverview of DNS• MotivationMotivation• PK-DNSSECPK-DNSSEC• SK-DNSSECSK-DNSSEC• Comparison with PK-DNSSEC• Usage of DNSSECUsage of DNSSEC

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.

Performance

(800M HZ)

Performance (cont.)

Network Traffic

Storage

Outline• Overview of DNSOverview of DNS• MotivationMotivation• PK-DNSSECPK-DNSSEC• SK-DNSSECSK-DNSSEC• Comparison with PK-DNSSECComparison with PK-DNSSEC• Usage of DNSSEC

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

Q&A

Thank You!