DNS Security Extension

1

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

2

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

3

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

4

5Borrowed from slides of Prof. Dan Massey

at Colorado State University

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

ciscousf coibm

cse

The Domain Name System

6Adapted from slides of Prof. Dan Massey

at Colorado State University

Provides a “natural” PKI 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 for its zone

Root

edu com uk

ciscousf coibm

cse

DNSSEC

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)

…

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• Introduce a new data type: RRSIG name TTL class type value

{www.usf.edu. 82310 IN A 131.247.182.171}

name TTL class type covered_type

{www.usf.edu. 82310 IN RRSIG A …

20151216023910

20141216023910 … usf.edu.

Base 64 encoding of signature}

DNSSEC Records

not after

not before key name

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• Introduce a new data type: DNSKEY name TTL class type value

{ usf.edu. 82310 IN DNSKEY Base 64 encoding

of public key}

name TTL class type covered_type

{ usf.edu. 82310 IN RRSIG DNSKEY …

20151216023910

20141216023910 … edu.

Base 64 encoding of signature}

DNSSEC Records

not afternot before key name

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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 global.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

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PKusf2

Sig{PKusf }PKedu

sign

Key Management

NS for .edu

NS for usf.edu

PKedu

PKusf

DS Record

PKsigningDo not need to notify parent if changed

…

PKusf2

Want to change PKusf to PKusf2

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Potential Usage of DNSSEC

• If successfully deployed, DNSSEC can serve as a universal Public Key Infrastructure (PKI)– Sign public keys for web sites

– Sign public keys for email addresses

• Can this really be achieved?– Existing systems like X.509 have so far failed to provide a

universal PKI

– DNSSEC has a major difference from X.509

• Key compromise at a node only affects a subdomain

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SSL/TLS

Alice Bob

E(PKB , s)

KC, KM = h(s)

PKB

PKB is Bob’s public key

I am Bob, inc

I am Alice

{m}KC || MACKM

(m)

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

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Advantages of DANE compared with X.509

• Real delegation of power– Better accountability– More flexibility– Better damage control

• Clearer semantics– X.509 certificate encompasses everything– DANE records only means that “this domain’s

owner says…”

15

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 public keys 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

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Deployment Status

• Has been on-going for a number of years– Check status:http://www.dnssec-deployment.org/

http://www.internetsociety.org/deploy360/dnssec/maps/

• 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

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