privacy at the communication layercarmelatroncoso.com/cs-721/cs-721-tor-troncoso.pdf ·...
TRANSCRIPT
![Page 1: Privacy at the communication layercarmelatroncoso.com/cs-721/CS-721-tor-Troncoso.pdf · 2018-03-18 · Tor directory servers. Directory tor Relays. 10 directory servers. Every hour:](https://reader033.vdocuments.mx/reader033/viewer/2022042300/5ecb8b67b4d6d443cf508627/html5/thumbnails/1.jpg)
Privacy at the communication layer
CS-721
Carmela Troncoso http://carmelatroncoso.com/
Tor: The Second-Generation Onion Router Roger Dingledine, Nick Mathewson, 2004
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Alice Bob
Tor directory servers
Directory tor Relays
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Alice Bob
Tor directory servers
Directory tor Relays
10 directory servers
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Alice Bob
Tor directory servers
Directory tor Relays
10 directory servers
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Tor directory servers
Directory tor Relays
10 directory servers
Every hour:
- DAs compile a list of all known relays & flags & stuff- DAs submits this “status-vote” to all the other authorities (DAs collect missing)- DAs cobine parameters, sign and send to the other DA’s
- There should be a majority agreeing on the data -> consensus
- Consensus published by each DA
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Tor directory servers
Directory tor Relays
10 directory servers
Every hour:
- DAs compile a list of all known relays & flags & stuff- DAs submits this “status-vote” to all the other authorities (DAs collect missing)- DAs cobine parameters, sign and send to the other DA’s
- There should be a majority agreeing on the data -> consensus
- Consensus published by each DA
https://metrics.torproject.org/collector.html
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Alice Bob
Tor directory servers
Directory tor Relays
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Bob
The Tor Network
But can Block Tor!
Directory tor Relays
Alice
Anonymous???
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Bob
The Tor Network
But can Block Tor!
Directory tor ALLRelays
Alice
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Bob
The Tor Network
But can Block Tor!
Directory tor ALLRelays
Alice
Choice is local!
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Bob
The Tor Network
But can Block Tor!
Directory tor ALLRelays
Alice
Choice is local!
Private information retrieval!
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Bob
The Tor Network
But can Block Tor!
Directory tor ALLRelays
Alice
Choice is local!
Private information retrieval!(scalability could be a problem)
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Bob
The Tor Network
But can Block Tor!
Directory tor Relays
Alice
“Lack of deniability”
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Bob
The Tor Network
But can Block Tor!
Directory tor Relays
Alice
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Bob
The Tor Network
But can Block Tor!
Directory tor Relays
Alice
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Censorship circumvention - Bridges
Bob
IPs not publicly available
Alice
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Censorship circumvention – finding Bridges
Bob
web email
Bridge IP
Alice
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Censorship circumvention – finding Bridges
Bob
web email
Bridge IP
default
Alice
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Censorship circumvention – finding Bridges
Bob
web email
Bridge IP
default
Privatebridges
Alice
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Alice Bob
IPs not publicly available
Censorship circumvention – finding Bridges
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Alice Bob
IPs not publicly available
Censorship circumvention – finding Bridges
Can we find or enumerate?
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Bob
IPs not publicly available
Censorship circumvention – finding Bridges
Can we find or enumerate?
Alice
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Bob
IPs not publicly available
Censorship circumvention – finding Bridges
Can we find or enumerate?
Alice
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Bob
IPs not publicly available
Censorship circumvention – finding Bridges
Can we find or enumerate?
Alice
Directory tor ALLRelays
?
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Bob
IPs not publicly available
Censorship circumvention – finding Bridges
Can we find or enumerate?
Alice
Directory tor ALLRelays
?Onion router
Bridge
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We exploit...
1. Vanilla Tor Certificates− Vanilla Tor uses TLS handshake− Easy to spot certificates− It won’t be fixed
Two issues known to Tor project since October 2010
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We exploit...
1. Vanilla Tor Certificates− Vanilla Tor uses TLS handshake− Easy to spot certificates− It won’t be fixed
2. Open OR Port− Bridges have open OR Port with Vanilla Tor− Even if they do not offer Vanilla Tor− Difficult to fix
Two issues known to Tor project since October 2010
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We exploit...
1. Vanilla Tor Certificates− Vanilla Tor uses TLS handshake− Easy to spot certificates− It won’t be fixed
2. Open OR Port− Bridges have open OR Port with Vanilla Tor− Even if they do not offer Vanilla Tor− Difficult to fix
Two issues known to Tor project since October 2010
Why don’t we scan all IPs with TLS to find
bridges?
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We exploit...
1. Vanilla Tor Certificates− Vanilla Tor uses TLS handshake− Easy to spot certificates− It won’t be fixed
2. Open OR Port− Bridges have open OR Port with Vanilla Tor− Even if they do not offer Vanilla Tor− Difficult to fix
Two issues known to Tor project since October 2010
Why don’t we scan all IPs with TLS to find
bridges?
![Page 30: Privacy at the communication layercarmelatroncoso.com/cs-721/CS-721-tor-Troncoso.pdf · 2018-03-18 · Tor directory servers. Directory tor Relays. 10 directory servers. Every hour:](https://reader033.vdocuments.mx/reader033/viewer/2022042300/5ecb8b67b4d6d443cf508627/html5/thumbnails/30.jpg)
We exploit...
1. Vanilla Tor Certificates− Vanilla Tor uses TLS handshake− Easy to spot certificates− It won’t be fixed
2. Open OR Port− Bridges have open OR Port with Vanilla Tor− Even if they do not offer Vanilla Tor− Difficult to fix
Two issues known to Tor project since October 2010
Why don’t we scan all IPs with TLS to find
bridges?
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We use three datasets
Scan 6 ports with TLSRaw + indexed data available
Scan 200+ ports with multiple protocols19 ports scanned with TLSIndexed data available
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We use three datasets
Scan 6 ports with TLSRaw + indexed data available
Scan 200+ ports with multiple protocols19 ports scanned with TLSIndexed data available
Identify candidate bridge IPs (without scanning ourselves!!)
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We use three datasets
Node-level data on public bridges + relaysSome bridge data sanitized
Scan 6 ports with TLSRaw + indexed data available
Scan 200+ ports with multiple protocols19 ports scanned with TLSIndexed data available
Identify candidate bridge IPs (without scanning ourselves!!)
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We use three datasets
Node-level data on public bridges + relaysSome bridge data sanitized
Scan 6 ports with TLSRaw + indexed data available
Scan 200+ ports with multiple protocols19 ports scanned with TLSIndexed data available
Identify candidate bridge IPs (without scanning ourselves!!)
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Bridge discovery approach
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1. Finding candidate IP addresses
2.
Bridge discovery approach
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1. Finding candidate IP addresses
2. Filtering relays
3.
Bridge discovery approach
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1. Finding candidate IP addresses
2. Filtering relays
3. Verifying IP addresses
4.
Bridge discovery approach
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1. Finding candidate IP addresses
2. Filtering relays
3. Verifying IP addresses
4. Identifying private proxies− (check descriptor)
5.
Bridge discovery approach
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1. Finding candidate IP addresses
2. Filtering relays
3. Verifying IP addresses
4. Identifying private proxies− (check descriptor)
5. Classifying as public or private bridge− (find sanitized fingerprint)
Bridge discovery approach
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Public bridges - population
April 2016:• 5.3K active public bridges• 2.3K bridges with clients
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Tor Hidden services
DB
XYZ.onion
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Tor Hidden services
DB
IP1
IP2
IP3
XYZ.onion
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Tor Hidden services
DB
IP1
IP2
IP3
XYZ.onion
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Tor Hidden services
DB
IP1
IP2
IP3
Sig (IP1, IP2, IP3)
XYZ.onion
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Tor Hidden services
DB
IP1
IP2
IP3
XYZ.onion
XYZ.onion ?
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Tor Hidden services
DB
IP1
IP2
IP3
XYZ.onion
XYZ.onion ?
RV
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Tor Hidden services
DB
IP1
IP2
IP3
XYZ.onion
RV
Sig (IP1, IP2, IP3)
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Tor Hidden services
DB
IP1
IP2
IP3
XYZ.onion
RV
E (RP)
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Tor Hidden services
DB
IP1
IP2
IP3
XYZ.onion
RV
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Locating Tor Hidden services
DB
IP1
IP2
IP3
XYZ.onion
RV
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Locating Tor Hidden services
DB
IP1
IP2
IP3
XYZ.onion
RV
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Locating Tor Hidden services
DB
IP1
IP2
IP3
XYZ.onion
RV
![Page 54: Privacy at the communication layercarmelatroncoso.com/cs-721/CS-721-tor-Troncoso.pdf · 2018-03-18 · Tor directory servers. Directory tor Relays. 10 directory servers. Every hour:](https://reader033.vdocuments.mx/reader033/viewer/2022042300/5ecb8b67b4d6d443cf508627/html5/thumbnails/54.jpg)
DHT – distributed hash table
Tor Hidden services
DB
stuff
cookietime
![Page 55: Privacy at the communication layercarmelatroncoso.com/cs-721/CS-721-tor-Troncoso.pdf · 2018-03-18 · Tor directory servers. Directory tor Relays. 10 directory servers. Every hour:](https://reader033.vdocuments.mx/reader033/viewer/2022042300/5ecb8b67b4d6d443cf508627/html5/thumbnails/55.jpg)
DHT – distributed hash table
Tor Hidden services
DB
stuff
cookietime
Set up an HSDir and log all hidden service descriptors published to their node. (profile client requests)
Predictable descriptor ID’s & HSDircontrolled => DoS particular HS
![Page 56: Privacy at the communication layercarmelatroncoso.com/cs-721/CS-721-tor-Troncoso.pdf · 2018-03-18 · Tor directory servers. Directory tor Relays. 10 directory servers. Every hour:](https://reader033.vdocuments.mx/reader033/viewer/2022042300/5ecb8b67b4d6d443cf508627/html5/thumbnails/56.jpg)
DHT – distributed hash table
Tor Hidden services
DB
stuff
cookietime
Set up an HSDir and log all hidden service descriptors published to their node. (profile client requests)
Predictable descriptor ID’s & HSDircontrolled => DoS particular HS
![Page 57: Privacy at the communication layercarmelatroncoso.com/cs-721/CS-721-tor-Troncoso.pdf · 2018-03-18 · Tor directory servers. Directory tor Relays. 10 directory servers. Every hour:](https://reader033.vdocuments.mx/reader033/viewer/2022042300/5ecb8b67b4d6d443cf508627/html5/thumbnails/57.jpg)
Honions – detecting malicious HDirs
not advertisedno functionality
![Page 58: Privacy at the communication layercarmelatroncoso.com/cs-721/CS-721-tor-Troncoso.pdf · 2018-03-18 · Tor directory servers. Directory tor Relays. 10 directory servers. Every hour:](https://reader033.vdocuments.mx/reader033/viewer/2022042300/5ecb8b67b4d6d443cf508627/html5/thumbnails/58.jpg)
Cascade vs. Free routes
Senders
Receivers
Senders
Receivers
![Page 59: Privacy at the communication layercarmelatroncoso.com/cs-721/CS-721-tor-Troncoso.pdf · 2018-03-18 · Tor directory servers. Directory tor Relays. 10 directory servers. Every hour:](https://reader033.vdocuments.mx/reader033/viewer/2022042300/5ecb8b67b4d6d443cf508627/html5/thumbnails/59.jpg)
Cascade vs. Free routes
Senders
Receivers
Senders
Receivers
No choice for users
Full flexibility
![Page 60: Privacy at the communication layercarmelatroncoso.com/cs-721/CS-721-tor-Troncoso.pdf · 2018-03-18 · Tor directory servers. Directory tor Relays. 10 directory servers. Every hour:](https://reader033.vdocuments.mx/reader033/viewer/2022042300/5ecb8b67b4d6d443cf508627/html5/thumbnails/60.jpg)
Cascade vs. Free routes
Senders
Receivers
Senders
Receivers
Small set of people / Professionals
Peers, unknown, volunteers
![Page 61: Privacy at the communication layercarmelatroncoso.com/cs-721/CS-721-tor-Troncoso.pdf · 2018-03-18 · Tor directory servers. Directory tor Relays. 10 directory servers. Every hour:](https://reader033.vdocuments.mx/reader033/viewer/2022042300/5ecb8b67b4d6d443cf508627/html5/thumbnails/61.jpg)
Cascade vs. Free routes
Senders
Receivers
Senders
Receivers
Partitioned anonymity
sets
![Page 62: Privacy at the communication layercarmelatroncoso.com/cs-721/CS-721-tor-Troncoso.pdf · 2018-03-18 · Tor directory servers. Directory tor Relays. 10 directory servers. Every hour:](https://reader033.vdocuments.mx/reader033/viewer/2022042300/5ecb8b67b4d6d443cf508627/html5/thumbnails/62.jpg)
Cascade vs. Free routes
Senders
Receivers
Senders
Receivers
Partitioned anonymity
sets
and here?
![Page 63: Privacy at the communication layercarmelatroncoso.com/cs-721/CS-721-tor-Troncoso.pdf · 2018-03-18 · Tor directory servers. Directory tor Relays. 10 directory servers. Every hour:](https://reader033.vdocuments.mx/reader033/viewer/2022042300/5ecb8b67b4d6d443cf508627/html5/thumbnails/63.jpg)
What is tor?
Senders
Receivers
Senders
Receivers
and here?
![Page 64: Privacy at the communication layercarmelatroncoso.com/cs-721/CS-721-tor-Troncoso.pdf · 2018-03-18 · Tor directory servers. Directory tor Relays. 10 directory servers. Every hour:](https://reader033.vdocuments.mx/reader033/viewer/2022042300/5ecb8b67b4d6d443cf508627/html5/thumbnails/64.jpg)
What is tor?
Senders
Receivers
Senders
Receivers
![Page 65: Privacy at the communication layercarmelatroncoso.com/cs-721/CS-721-tor-Troncoso.pdf · 2018-03-18 · Tor directory servers. Directory tor Relays. 10 directory servers. Every hour:](https://reader033.vdocuments.mx/reader033/viewer/2022042300/5ecb8b67b4d6d443cf508627/html5/thumbnails/65.jpg)
What is tor?
Senders
Receivers
Stratified
![Page 66: Privacy at the communication layercarmelatroncoso.com/cs-721/CS-721-tor-Troncoso.pdf · 2018-03-18 · Tor directory servers. Directory tor Relays. 10 directory servers. Every hour:](https://reader033.vdocuments.mx/reader033/viewer/2022042300/5ecb8b67b4d6d443cf508627/html5/thumbnails/66.jpg)
Are there more options?
Source based vs. non-source routing
Next week Crowds: Anonymity for Web Transactions
![Page 67: Privacy at the communication layercarmelatroncoso.com/cs-721/CS-721-tor-Troncoso.pdf · 2018-03-18 · Tor directory servers. Directory tor Relays. 10 directory servers. Every hour:](https://reader033.vdocuments.mx/reader033/viewer/2022042300/5ecb8b67b4d6d443cf508627/html5/thumbnails/67.jpg)
Key takeaways
Anonymity is hardnot only need users… too many variables
Peer-oriented is problematic – cannot check identitiesMalicious nodes can infiltrate (HS, Bridges, full anonymity)
Different Routing options = properties – more next week