Dissecting Tor Bridges A Security Evaluation of their Private and Public Infrastructures
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1 Dissecting Tor Bridges A Security Evaluation of their Private and Public Infrastructures Srdjan Matic, Carmela Troncoso, Juan Caballero Dublin 31 March 2017
2 Privacy in electronic communications Alice Bob A Network
3 Privacy in electronic communications Dear Dr. Bob, Can we change my chemo appointment? A. Alice Bob A Network
4 Privacy in electronic communications Alice Bob A Network
5 Privacy in electronic communications Alice Bob A Network
6 Privacy in electronic communications SysAdmins Alice Bob A Network
7 Privacy in electronic communications SysAdmins Alice Bob A Network
8 Privacy in electronic communications Bob A Network
9 Privacy in electronic communications Bob A Network
10 Privacy in electronic communications A Network
11 But we can encrypt! What is the problem? Alice Bob A Network
12 But we can encrypt! What is the problem? Alice Bob
13 But we can encrypt! What is the problem? Alice Bob
14 But we can encrypt! What is the problem? Alice Bob
15 But we can encrypt! What is the problem? Alice Bob
16 But we can encrypt! What is the problem? Alice Bob
17 But we can encrypt! What is the problem? Alice Bob
18 The problem is Traffic Analysis!! Alice Bob
19 Traffic analysis resistance: Anonymous communications Receivers Senders Bitwise unlinkability Crypto to make inputs and outputs bit patterns different (re)packetizing + (re)schedule + (re)routing, Destroy patterns (traffic analysis resistance) Load balancing Distribute trust
20 The Tor Network
21 The Tor Network
22 The Tor Network
23 The Tor Network
24 The Tor Network
25 The Tor Network
26 The Tor Network
27 The Tor Network - Goals Surveillance and monitoring protection
28 The Tor Network - Goals Surveillance and monitoring protection
29 The Tor Network - Goals Surveillance and monitoring protection
30
31
32
33
34
35 Censorship circumvention - Bridges
36 Censorship circumvention finding Bridges
37 Censorship circumvention finding Bridges
38 Censorship circumvention finding Bridges
39 What about Traffic analysis?
40 What about Traffic analysis? ~
41 What about Traffic analysis? ~
42 What about Traffic analysis? ~
43 What about Traffic analysis? Pluggable transports ~
44 Studying Bridges ❶ Onion Router whose IP is not publicly listed ❷ is always elected as the first hop ❸ can offer multiple Pluggable Transports.
45 Studying Bridges Our goals ❶ Onion Router whose IP is not publicly listed ❷ is always elected as the first hop ❸ can offer multiple Pluggable Transports. Perform first systematic study of the security of the Tor bridge infrastructure
46 Studying Bridges Our goals ❶ Onion Router whose IP is not publicly listed ❷ is always elected as the first hop ❸ can offer multiple Pluggable Transports.
47 Studying Bridges Our goals ❶ Onion Router whose IP is not publicly listed ❷ is always elected as the first hop ❸ can offer multiple Pluggable Transports.
48 We exploit... Two issues known to Tor project since October Vanilla Tor Certificates Vanilla Tor uses TLS handshake Easy to spot certificates It won t be fixed
49 We exploit... Two issues known to Tor project since October Vanilla Tor Certificates Vanilla Tor uses TLS handshake Easy to spot certificates It won t be fixed
50 We exploit...
51 We exploit...
52 We use three datasets Scan 200+ ports with multiple protocols 19 ports scanned with TLS Indexed data available Scan 6 ports with TLS Raw + indexed data available
53 We use three datasets Scan 200+ ports with multiple protocols 19 ports scanned with TLS Indexed data available Scan 6 ports with TLS Raw + indexed data available Identify candidate bridge IPs (without scanning ourselves!!)
54 We use three datasets Scan 200+ ports with multiple protocols 19 ports scanned with TLS Indexed data available Scan 6 ports with TLS Raw + indexed data available Identify candidate bridge IPs (without scanning ourselves!!)
55 We use three datasets Scan 200+ ports with multiple protocols 19 ports scanned with TLS Indexed data available Scan 6 ports with TLS Raw + indexed data available Identify candidate bridge IPs (without scanning ourselves!!)
56 Bridge discovery approach
57 Bridge discovery approach 1. Finding candidate IP addresses
58 Bridge discovery approach 1. Finding candidate IP addresses 2. Filtering relays
59 Bridge discovery approach 1. Finding candidate IP addresses ~
60 Bridge discovery approach 1. Finding candidate IP addresses ~ 4. Identifying private proxies (check descriptor)
61 Bridge discovery approach 1. Finding candidate IP addresses ~
62 Public bridges - population
63 Public bridges - population April 2016: 5.3K active public bridges 2.3K bridges with clients
64 Public bridges - population April 2016: 5.3K active public bridges 2.3K bridges with clients Different population metrics!
65 Public bridges - stability 55% of the bridges live < 1 day No clients Bridges with clients long lived 4 months (median) Bridges with clients rarely change IP address
66 Public bridges - stability
67 Public bridges PT deployment April 2016
68 Public bridges PT deployment April 2016
69 Public bridges PT deployment April 2016
70 Public bridges OR port distribution
71 Public bridges OR port distribution Top-3 OR ports ( 444) are used by 71% of public bridges (99% of active fingerprints never change their OR port)
72 Public bridges OR port distribution Top-3 OR ports ( 444) are used by 71% of public bridges (99% of active fingerprints never change their OR port) Scanning on those ports reveals majority of bridges!
73 Public bridges OR port distribution
74 Public bridges Ranking Not all bridges are equally important!!
75 Public bridges Ranking Not all bridges are equally important!! How well is country-level blocking working? Which bridges should censor target next?
76 Public bridges Ranking Not all bridges are equally important!! How well is country-level blocking working? Which bridges should censor target next? 91% traffic used default bridges! A censor can disconnect users in reaction to an event
77 Public bridges Ranking Not all bridges are equally important!! How well is country-level blocking working? Which bridges should censor target next? 91% traffic used default bridges! A censor can disconnect users in reaction to an event How well is blocking of specific PT working?
78 Public bridges Ranking Not all bridges are equally important!! How well is country-level blocking working? Which bridges should censor target next? 91% traffic used default bridges! A censor can disconnect users in reaction to an event How well is blocking of specific PT working? 94% obs4 in default! Useless reply protection...
79 Public bridges Ranking
80 Private bridges Population (Apr 2016)
81 Private bridges Population (Apr 2016) Deanonymized 35% public bridges with clients
82 Private bridges Population (Apr 2016) Deanonymized 35% public bridges with clients Found 684 private bridges private proxies
83 Private bridges Population (Apr 2016) Deanonymized 35% public bridges with clients Found 684 private bridges private proxies 175 non-public domains in contact info (307 bridges 187 public /180 private)
84 Private bridges clustering (verifiedip, OR port, descriptor) 41,359 tuples Clustering 1,343 clusters (75% singletons) Features: Same fingerprint Similar nicknames Same contact information Similar verified IP address (+ identical config ) Simlar IP address in descriptor (+ identical config )
85 Private bridges clustering
86 Bonus track tracking bridges ssh telnet mongodb https additional service and 10% more than one.
87 Bonus track tracking bridges ssh telnet mongodb additional service and 10% more than one. https Most common additional services: SSH - ports 22 and 2222, Web services - ports 80 and 443 RPC port mapper - port 111
88 Bonus track tracking bridges ssh telnet mongodb additional service and 10% more than one. https Most common additional services: SSH - ports 22 and 2222, Web services - ports 80 and 443 RPC port mapper - port 111 Unique identifiers SSH keys Certificate serial numbers
89 Bonus track tracking bridges ssh telnet mongodb https additional service and 10% more than one.
90 Bonus track tracking bridges ssh telnet mongodb https additional service and 10% more than one.
91 Conclusion - Security Implications Public Bridges Bridges with clients live 4 months, no IP changes Blocking PTs with conflicting security properties Top-3 OR ports 71% public bridges Patch CollecTor 91% bridge traffic uses default bridges Defeats purpose Bridge Ranking enables targeted attacks
92 Conclusion - Security Implications Public Bridges Bridges with clients live 4 months, no IP changes Blocking PTs with conflicting security properties Top-3 OR ports 71% public bridges Patch CollecTor 91% bridge traffic uses default bridges Defeats purpose Bridge Ranking enables targeted attacks Bridge discovery Deanonymized 35% of public bridges Found 684 private bridges private proxies 35% bridges are private Clusters of bridges+proxies deployed Little IP diversity
93 Conclusion - Security Implications Public Bridges Bridges with clients live 4 months, no IP changes Blocking PTs with conflicting security properties Top-3 OR ports 71% public bridges Patch CollecTor 91% bridge traffic uses default bridges Defeats purpose Bridge Ranking enables targeted attacks Bridge discovery Deanonymized 35% of public bridges Found 684 private bridges private proxies 35% bridges are private Clusters of bridges+proxies deployed Little IP diversity Open OR Port needs fixing!!!!
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