Privacy: anonymous routing, mix nets (Tor), in addition to user tracking Anonymous web browsing Current state of the world I Current state of the world II Part 1: network-layer privacy

Privacy: 	anonymous routing, 	mix nets (Tor), in addition to 	user tracking Anonymous web browsing Current state of the world I Current state of the world II Part 1: network-layer privacy www.phwiki.com

Privacy: anonymous routing, mix nets (Tor), in addition to user tracking Anonymous web browsing Current state of the world I Current state of the world II Part 1: network-layer privacy

Manaugh, Geoff, Contributing Editor has reference to this Academic Journal, PHwiki organized this Journal Privacy: anonymous routing, mix nets (Tor), in addition to user tracking Anonymous web browsing Why Discuss health issues or financial matters anonymously Bypass Internet censorship in parts of the world Conceal interaction with gambling sites Law en as long as cement Two goals: Hide user identity from target web site: (1), (4) Hide browsing pattern from employer or ISP: (2), (3) Stronger goal: mutual anonymity (e.g. remailers) Current state of the world I ISPs tracking customer browsing habits: Sell in as long as mation to advertisers Embed targeted ads in web pages (1.3%) Example: MetroFi (free wireless) [Web Tripwires: Reis et al. 2008] Several technologies used as long as tracking at ISP: NebuAd, Phorm, Front Porch Bring together advertisers, publishers, in addition to ISPs At ISP: inject targeted ads into non-SSL pages Tracking technologies at enterprise networks: Vontu (symantec), Tablus (RSA), Vericept

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Current state of the world II EU directive 2006/24/EC: 3 year data retention For ALL traffic, requires EU ISPs to record: Sufficient in as long as mation to identify endpoints (both legal entities in addition to natural persons) Session duration but not session contents Make available to law en as long as cement but penalties as long as transfer or other access to data For info on US privacy on the net: “privacy on the line” by W. Diffie in addition to S. L in addition to au Part 1: network-layer privacy Goals: Hide user’s IP address from target web site Hide browsing destinations from network 1st attempt: anonymizing proxy HTTPS:// anonymizer.com URL=target User1 User2 User3 anonymizer.com Web1 Web2 Web3 SSL HTTP

Anonymizing proxy: security Monitoring ONE link: eavesdropper gets nothing Monitoring TWO links: Eavesdropper can do traffic analysis More difficult if lots of traffic through proxy Trust: proxy is a single point of failure Can be corrupt or subpoenaed Example: The Church of Scientology vs. anon.penet.fi Protocol issues: Long-lived cookies make connections to site linkable How proxy works Proxy rewrites all links in response from web site Updated links point to anonymizer.com Ensures all subsequent clicks are anonymized Proxy rewrites/removes cookies in addition to some HTTP headers Proxy IP address: if a single address, could be blocked by site or ISP anonymizer.com consists of >20,000 addresses Globally distributed, registered to multiple domains Note: chinese firewall blocks ALL anonymizer.com addresses Other issues: attacks (click fraud) through proxy 2nd Attempt: MIX nets Goal: no single point of failure

Epk2( R3, Epk3( R6, MIX nets [C’81] Every router has public/private key pair Sender knows all public keys To send packet: Pick r in addition to om route: R2 R3 R6 srvr Prepare onion packet: R3 R5 R4 R1 R2 R6 Epk6( srvr , msg) msg srvr packet = Eavesdropper’s view at a single MIX Eavesdropper observes incoming in addition to outgoing traffic Crypto prevents linking input/output pairs Assuming enough packets in incoming batch If variable length packets then must pad all to max len Note: router is stateless Ri batch Per as long as mance Main benefit: Privacy as long as at least one honest router on path Problems: High latency (lots of public key ops) Inappropriate as long as interactive sessions May be OK as long as email (e.g. Babel system) No as long as ward security Homework puzzle: how does server respond hint: user includes “response onion” in as long as ward packet R3 R2 R6 srvr

3rd Attempt: Tor MIX circuit-based method Goals: privacy as long as one honest router on path, in addition to reasonable per as long as mance The Tor design Trusted directory contains list of Tor routers User’s machine preemptively creates a circuit Used as long as many TCP streams New circuit is created once a minute R1 R2 R3 R4 srvr1 srvr2 R5 R6 one minute later stream1 stream2 Creating circuits R1 R2 TLS encrypted TLS encrypted K1 K1 K2 K2

Once circuit is created User has shared key with each router in circuit Routers only know ID of successor in addition to predecessor R1 R2 R3 R4 K1, K2, K3, K4 K1 K2 K3 K4 Sending data R1 R2 K1 K2 Properties Per as long as mance: Fast connection time: circuit is pre-established Traffic encrypted with AES: no pub-key on traffic Tor crypto: provides end-to-end integrity as long as traffic Forward secrecy via TLS Downside: Routers must maintain state per circuit Each router can link multiple streams via CircuitID all steams in one minute interval share same CircuitID

Privoxy Tor only provides network level privacy No application-level privacy e.g. mail progs add “From: email-addr” to outgoing mail Privoxy: Web proxy as long as browser-level privacy Removes/modifies cookies Other web page filtering Anonymity attacks: watermarking Goal: R1 in addition to R3 want to test if user is communicating with server Basic idea: R1 in addition to R3 share sequence: 1, 2, , n {-10, ,10} R1: introduce inter-packet delay to packets leaving R1 in addition to bound as long as R2 . Packet i delayed by i (ms) Detect signal at R3 R1 R2 R3 Anonymity attacks: congestion Main idea: R8 can send Tor traffic to R1 in addition to measure load on R1 Exploit: malicious server wants to identify user Server sends burst of packets to user every 10 seconds R8 identifies when bursts are received at R1 Follow packets from R1 to discover user’s ID R1 R2 R3 R8

Web-based user tracking Browser provides many ways to track users: 3rd party cookies ; Flash cookies Tracking through the history file Machine fingerprinting 3rd party cookies What they are: User goes to site A. com ; obtains page Page contains