Anonymizing Protocols

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Augusta Merel de Ruiter
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1 nonymizing Protocols Peter van ossum adboud University Nijmegen

2 Motivation Electronic Voting Dining Cryptographers Network nalysis Communication Sender nonymity [ anonymous webbrowsing ] eceiver nonymity [ anonymous webserving ] Censorship esistance

3 Historical Overview nonymous r ers 1993 anon.penet.fi 2003 MixMinion nonymous publishing 1999 Freenet (peer-to to-peer) nonymous webbrowsing / general 1996 Onion outing (original idea Chaum 1981) 1998 Crowds (peer-to to-peer) 2003 Tor (successor of Onion outing) 2003 Tarzan, MorphMix (peer-to to-peer)

4 nonymous r ers/webbrowsing Forward messages via one or more relays nonymous r er Crowds: peer-to to-peer, no encryption Onion outing: layered encryptions Tor: : extensible communication channels

5 nonymizing Proxy,m m m Sender anonymity No anonymity vs. observer of

6 Crowds,m 1 m Sender anonymity No anonymity vs. global observer

7 Crowds,m 1,m 3,m m 2 Sender anonymity No anonymity vs. global observer Probabilistic Forwarding

8 Onion outing { 2,{ 3,{,m} 3 } 2 } m 2 nonymity vs. global observer

9 Onion outing { 2,{ 3,{,m} 3 } 2 } { 3,{,m} 3 } 2 {,m} 3 m 2 nonymity vs. global observer

10 Tor: : Circuits tor-aware connection 1 2 ordinary connection

11 Tor: : Circuits {{m} 2 } 1 tor-aware connection 1 {m} 2 2 m ordinary connection

12 Tor: : Circuits

13 Tor: : Circuits {{X}} {X} - Single - Double Onion Onion

14 nonymous publishing/webserving Serve content via relays Freenet: : data-based, peer-to to-peer Tor: : server-based, rendezvous-points

15 Freenet nonymous Publishing Documents (instead of agents) Censorship resistance

16 Freenet: : outing GUID (Globally Unique Identifier) CHK (Content Hash Key) hash(data) Content SSK (Signed Subspace Key) hash( hash(pk) hash(description) ) ) ( Publisher has/is (pk,sk( pk,sk) ) ) {CHK hash(data)} sk eni8yfo3gj8uvh-u0hpkmftf6qqge/homepage/website_howto.html eni8yfo3gj8uvh-u0hpkmftf6qqge/files/0.16a/manifest.jar pk description

17 Every node keeps table Freenet: : outing neighbor 1 (ip-address) guid 1 guid 2 neightbor 2 (ip-address) guid 3 guid 4 equest for guid gets forwarded to neighbor with closest guid Data ripples back along path

18 Freenet: : outing

19 Freenet: : outing Nodes accumulate files with similar hash-values

20 Tor nonymous service [ webserver ] Initializition points serve as proxies for server endezvous points serve as proxies for client

21 Tor: : nonymous Publishing DS P IP 1 IP 2 P data P data query description IP 1 description, IP 1, IP 2

22 Design esearch Subjects Latency vs. anonymity Incentive to participate Scalability nalysis Estimation of risk of specific attacks ttacker model Formal analysis of secrecy/authentication nonymization properties Formal analysis of anonymity

23 ttacker Model Dolev-Yao attacker too strong Global passive adversary + bility to corrupt nodes still too strong Partial passive adversary + bility to corrupt nodes practical analysis Global passive adversary theoretical analysis Computational adversary No formal concept yet of timing attacks, statistical traffic analysis attacks

24 Design esearch Subjects Latency vs. anonymity Incentive to participate Scalability nalysis Estimation of risk of specific attacks ttacker model Formal analysis of secrecy/authentication nonymization properties Formal analysis of anonymity

25 Formal nalysis {m} k {,{m} k } k {,{m } k } k {m} k {m } k {,{m} k } k {,{m } k } k {m } k {m} k runs look the same to global observer

26 Formal nalysis {,{m} k } k {,{m } k } k {m} k {m } k {,{m} k } k {,{m } k } k {m } k {m} k r ² spy ( communicated with )

27 Formal nalysis {} k,{m} k {m} k { } k,{m} k {m } k { } k,{m } k {m } k {} k,{m } k {m} k repeated messages global observer can discover communication pattern

28 Formal nalysis {} k,{m} k { } k,{m } k {m} k {m } k { } k,{m} k {} k,{m } k {m } k {m} k r ² ( spy communicated with ) r ² ( spy communicated with )

29 Formal nalysis {m} k C D h({m} k ) E global observer can discover pattern

30 Formal nalysis {m} k C D h({m} k ) E r ² spy ( and are linkable)

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