DNSSEC Privacy CS 161 Computer Security Prof Vern Paxson TAs Devdatta Akhawe Mobin Javed Matthias Vallentin http inst eecs berkeley edu cs161 April 5 2011 Today s Lecture Finish discussion of DNSSEC Ensuring that DNS results indeed match those from the corresponding authority A look at privacy Mechanisms practices that subvert it Technical measures to obtain it Securing DNS Lookups How can we ensure that when clients look up names with DNS they can trust the answers they receive Idea 1 do DNS lookups over TLS assuming either we run DNS over TCP or we use Datagram TLS Issues Performance DNS is very lightweight TLS is not Caching crucial for DNS scaling But then how do we keep authentication assurances Idea 2 make DNS results like certs I e a verifiable signature that guarantees who generated a piece of data signing happens off line Operation of DNSSEC DNSSEC standardized DNS security extensions currently being deployed 1 Suppose we look up mail google com simplified We get an answer from google com nameserver NS Plus signature for answer in Additional section purportedly signed by google com NS 2 Look up public key for google com NS That answer is signed by com NS 3 Look up public key for com NS That answer is signed by root NS 4 Root NS s public key is wired into our resolver All of these keys are cacheable Ordinary DNS mail google com Client mail google com A 1 2 3 4 ns1 google com DNSSEC mail google com Client mail google com A 1 2 3 4 SIG 0x1F92 9 ns1 google com google com Client google com KEY 0x828C E SIG 0x90A4 5 com s NS DNS mail google com Client mail google com A 1 2 3 4 ns1 google com DNSSEC mail google com Client mail google com A 1 2 3 4 SIG 0x1F92 9 This key ns1 google com google com Client google com KEY 0x828C E SIG 0x90A4 5 com s NS DNS mail google com Client mail google com A 1 2 3 4 ns1 google com DNSSEC mail google com Client mail google com A 1 2 3 4 SIG 0x1F92 9 google com Client google com KEY 0x828C E SIG 0x90A4 5 ns1 google com validates this signature com s NS DNS mail google com Client mail google com A 1 2 3 4 ns1 google com DNSSEC mail google com Client Similarly the root will mail google com A 1 2 3 4 return com s KEY which SIG 0x1F92 9 will validate this signature ns1 google com google com Client google com KEY 0x828C E SIG 0x90A4 5 com s NS DNS mail google com Client mail google com A 1 2 3 4 ns1 google com DNSSEC mail google com Client Client ns1 google com mail google com A 1 2 3 4 Finally we can validate SIG 0x1F92 9 the com KEY supposedly google com returned by the root using our hardwired knowledge com s NS of the root s public key google com KEY 0x828C E SIG 0x90A4 5 DNS mail google com Client DNSSEC ns1 google com mail google com 1 2 3 4 Upon completing all ofAthese signature validations we have strong confidence in the chain of signatures and thus in the correctness of the mail google com result mail google com Client mail google com A 1 2 3 4 SIG 0x1F92 9 ns1 google com google com Client google com KEY 0x828C E SIG 0x90A4 5 com s NS Issues With DNSSEC Issue 1 Replies are Big E g dig dnssec berkeley edu can return 2100 B DoS amplification Increased latency on low capacity links Headaches w older libraries that assume replies 512B Issue 2 Partial deployment Suppose com not signing though google com is Major practical concern What do we do Can wire additional key into resolver doesn t scale Or outsource to trusted third party lookaside Wire their key into resolver they sign numerous early adopters Issues With DNSSEC con t Issue 3 Partial deployment What do you do with unsigned unvalidated results If you trust them weakens incentive to upgrade If you don t trust them a whole lot of things break Issue 4 Negative results no such name What statement does the nameserver sign If gabluph google com doesn t exist then have to do dynamic key signing expensive for any bogus request DoS vulnerability Instead sign off line statements about order of names E g sign gabby google com followed by gabrunk google com Thus can see that gabluph google com can t exist But now attacker can enumerate all names that exist Issues With DNSSEC con t Issue 5 Who do you really trust For your laptop say who does all the grunt work of fetching keys validating DNSSEC signatures Convenient answer your laptop s local resolver which you acquire via DHCP in your local coffeeshop I e exactly the most feared potentially untrustworthy part of the DNS resolution process Alternatives Your laptop needs to do all the validation work itself Privacy Defining Privacy Privacy right to control who knows certain aspects about you your communications your activities Control over disclosure And ideally over subsequent use How much of an issue is this E g how much information about you do web sites learn as you surf Privacy Web Surfing The sites you visit learn The URLs you re interested in Google Bing also learns what you re searching for Your IP address Thus your service provider geo location Can often link you to other activity including at other sites Your browser s capabilities which OS you run which language you prefer Which URL you looked at that took you there Via Referer header Privacy Web Surfing con t Oh and also cookies Cookies state that server tells browser to store locally Name value pair plus expiration date Browser returns the state any time visiting the same site Where s the harm in that And are these used much anyway Let s remove all of our cookies We do a Google search on private browsing And we click on the top result Note that this mode is privacy from your family not from web sites Whoa we gained 11 cookies What on earth is Google tracking in this one It sticks around for 6 months Hmmm Mozilla is tracking us too And for 5 years They re even remembering just how we visited them And something else as we ll see in a bit until the End Of Time Without doing anything else we ve gained a 12th cookie MY IP Address We now do just one more operation opening the home page of www nytimes com What a lot of yummy cookies doubleclick net who s that And how did it get there from visiting www nytimes com Third Party Cookies How can a web site enable a third party to plant cookies in your browser later retrieve them Answer using a web bug Include on the site s page for example img src http doubleclick net ad gif width 1 height 1 Why would a site do …
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