A New Approach to DNS Security (DNSSEC)

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A New Approach to DNS Security (DNSSEC)

• Author
• Giuseppe Ateniese
• Stefan Mangard
• Presenter Liu, Xiaotao

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Outline

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

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Outline

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

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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

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A DNS tree
.
root
domain
.net
.com
top level
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DNS data

• 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
  193.0.1.162
• host25.dacht.net 2600 IN A 193.0.3.25

Label
ttl
class
type
rdata
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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
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DNS resolving
Question www.cnn.com
.
www.cnn.com A ?
dns.cs.umass.edu
lab.cs.umass.edu
resolver
ask .com server the ip address of .com server
stub resolver
www.cnn.com A ?
.com
www.cnn.com A ?
xxx.xxx.xxx.xxx
ask cnn.com server the ip address of cnn.com
server
add to cache
www.cnn.com A ?
xxx.xxx.xxx.xxx
cnn.com
www.cnn.com
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DNS Data flow
Zone administrator
Zone file
master
resolver
slaves
Dynamic updates
stub resolver
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Outline

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

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DNS Vulnerabilities
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
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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

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Outline

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

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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 parents
  private key
• In the ideal case, only one public KEY needs to
  be distributed off-band (the roots public KEY)

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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 parents 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

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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

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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

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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

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Verifying the tree
Question www.cnn.com
. (root)
www.cnn.com 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
www.cnn.com A ?
.com
www.cnn.com A ?
xxx.xxx.xxx.xxx
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
www.cnn.com A ?
SIG(xxx.xxx.xxx.xxx) by its private key
transaction signatures
www.cnn.com
cnn.com
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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

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Outline

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

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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.

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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
  roots public key

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Notation
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DNS Root Certificate
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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
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DNS Request to Intermediate Server
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DNS Request to Authoritative Server
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For mutual authentication
For any 0 ? i ? n
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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

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Hybrid Approach

• The root servers use PK-DNSSEC
• The top-level domains use SK-DNSSEC

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Outline

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

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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.

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Performance
(800M HZ)
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Performance (cont.)
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Network Traffic
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Storage
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Outline

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

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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

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QA

• Thank You!