Post on 23-Mar-2016
description
Memory-based DoS and Deanonymization Attacks on Tor
DCAPS SeminarOctober 11th, 2013
Rob JansenU.S. Naval Research Laboratoryrob.g.jansen@nrl.navy.mil
*Joint with Aaron Johnson, Florian Tschorsch, Björn Scheuermann
The Tor Anonymity Network
torproject.org
How Tor Works
How Tor Works
How Tor Works
How Tor Works
How Tor Works
Tor protocol aware
Tor Flow Control
exitentry
Tor Flow Control
One TCP Connection Between Each Relay,
Multiple Circuits
exitentry
Tor Flow Control
One TCP Connection Between Each Relay,
Multiple Circuits
Multiple Application Streams
exitentry
Tor Flow Control
No end-to-end TCP!
exitentry
Tor Flow Control
Tor protocol aware
exitentry
Tor Flow Control
Packaging End
DeliveryEnd
exitentry
Tor Flow Control
Packaging End
DeliveryEnd
exitentry
Tor Flow Control
1000 Cell Limit
SENDME Signal Every 100 Cells
exitentry
Outline
● The Sniper Attack– Low-cost memory consumption attack that disables
arbitrary Tor relays
● Deanonymizing Hidden Services– Using DoS attacks for deanonymization
● Countermeasures
The Sniper Attack
Start Download
Request
exitentry
The Sniper Attack
Reply
DATAexitentry
The Sniper AttackPackage and Relay DATA
DATA
DATAexitentry
The Sniper Attack
DATA
DATA
Stop Reading from Connection
DATA
Rexitentry
The Sniper Attack
DATADATADATADATADATADATA
Rexitentry
Flow Window Closed
The Sniper Attack
DATA
Periodically Send SENDME SENDME
R
DATADATADATADATADATA
exitentry
The Sniper Attack
DATA
DATA
DATADATADATADATADATADATA
Periodically Send SENDME SENDME
R
DATADATADATADATADATA
exitentry
Flow Window Opened
The Sniper Attack
DATA
DATA
DATADATADATADATADATADATA
R
DATADATADATADATADATA
exitentry
DATADATADATADATADATADATADATADATADATADATA
Out of Memory, Killed by OS
The Sniper Attack
DATA
DATA
DATADATADATADATADATADATA
R
DATADATADATADATADATA
exitentry
DATADATADATADATADATADATADATADATADATADATA
Use Tor to Hide
Memory Consumed over Time
Mean RAM Consumed, 50 Relays
Mean BW Consumed, 50 Relays
Speed of Sniper Attack
Direct AnonymousRelay Groups Select % 1 GiB 8 GiB 1 GiB 8 GiBTop Guard 1.7
Top 5 Guards 6.5
Top 20 Guards 19
Top Exit 3.2
Top 5 Exits 13
Top 20 Exits 35
Path Selection Probability ≈ Network Capacity
Speed of Sniper Attack
Direct AnonymousRelay Groups Select % 1 GiB 8 GiB 1 GiB 8 GiBTop Guard 1.7 0:01 0:18 0:02 0:14
Top 5 Guards 6.5 0:08 1:03 0:12 1:37
Top 20 Guards 19 0:45 5:58 1:07 8:56
Top Exit 3.2 0:01 0:08 0:01 0:12
Top 5 Exits 13 0:05 0:37 0:07 0:57
Top 20 Exits 35 0:29 3:50 0:44 5:52
Time (hours:minutes) to Consume RAM
Speed of Sniper Attack
Direct AnonymousRelay Groups Select % 1 GiB 8 GiB 1 GiB 8 GiBTop Guard 1.7 0:01 0:18 0:02 0:14
Top 5 Guards 6.5 0:08 1:03 0:12 1:37
Top 20 Guards 19 0:45 5:58 1:07 8:56
Top Exit 3.2 0:01 0:08 0:01 0:12
Top 5 Exits 13 0:05 0:37 0:07 0:57
Top 20 Exits 35 0:29 3:50 0:44 5:52
Time (hours:minutes) to Consume RAM
Speed of Sniper Attack
Direct AnonymousRelay Groups Select % 1 GiB 8 GiB 1 GiB 8 GiBTop Guard 1.7 0:01 0:18 0:02 0:14
Top 5 Guards 6.5 0:08 1:03 0:12 1:37
Top 20 Guards 19 0:45 5:58 1:07 8:56
Top Exit 3.2 0:01 0:08 0:01 0:12
Top 5 Exits 13 0:05 0:37 0:07 0:57
Top 20 Exits 35 0:29 3:50 0:44 5:52
Time (hours:minutes) to Consume RAM
Outline
● The Sniper Attack– Low-cost memory consumption attack that disables
arbitrary Tor relays
● Deanonymizing Hidden Services– Using DoS attacks for deanonymization
● Countermeasures
Hidden Services
HS
User wants to hide service
Hidden Services
entry IP
HS chooses and publishes
introduction point IP
HS
Hidden Services
entry IP
HS
Learns about HS on web
entry
Hidden Services
entry IP
HS
Builds Circuit to Chosen Rendezvous
Point RP
RP
entry
Hidden Services
entry IP
HS
Notifies HS of RP through IP
RP
entry
RP
entry
Hidden Services
entry IP
HS
RP
RP
entry
Hidden Services
entry IP
HS
Build New Circuit to
RP
RP
entry
RP
entry
Hidden Services
entry IP
HS
Communicate!
RP
entry
RP
entry
Deanonymizing Hidden Services
HS
RP
entry
Deanonymizing Hidden Services
HS
RP
Also runs a guard relay
entry
Deanonymizing Hidden Services
entry
HS
RP
RP
Build New Circuit to
RP
entry
Deanonymizing Hidden Services
entry
HS
RP
RP S&P 2006, S&P 2013
entry
Deanonymizing Hidden Services
entry
HS
RP
RP S&P 2013
PADDING
Send 50 Padding
Cells
entry
Deanonymizing Hidden Services
entry
HS
RP
RP
Identify HS entry if cell count = 52
S&P 2013
entry
Deanonymizing Hidden Services
entry
HS
RP
Sniper Attack,or any other DoS
entry
Deanonymizing Hidden Services
HS
RP
Choose new Entry Guard
entry
Deanonymizing Hidden Services
HS
RP
RP
entry
Deanonymizing Hidden Services
HS
RP
RP S&P 2006, S&P 2013
entry
Deanonymizing Hidden Services
HS
RP
RP
Send 50 Padding
Cells
S&P 2013
PADDING
entry
Deanonymizing Hidden Services
HS
RP
RP
Identify HS if cell count = 53
S&P 2013
Outline
● The Sniper Attack– Low-cost memory consumption attack that disables
arbitrary Tor relays
● Deanonymizing Hidden Services– Using DoS attacks for deanonymization
● Countermeasures
Countermeasures
● Sniper Attack Defenses– Authenticated SENDMEs– Queue Length Limit– Adaptive Circuit Killer
● Deanonymization Defenses– Entry-guard Rate-limiting– Middle Guards
Questions?
cs.umn.edu/~jansenrob.g.jansen@nrl.navy.mil
think like an adversary
Speed of Deanonymization
Guard BW(MiB/s)
Guard Probability
(%)Average # Rounds
Average # Sniped
Average Time (h)
1 GiB
Average Time (h)
8 GiB8.41 0.48 66 133 46 279
16.65 0.97 39 79 23 149
31.65 1.9 24 48 13 84
66.04 3.8 13 26 6 44
96.61 5.4 9 19 5 31
1 GiB/s Relay Can Deanonymize HS in
about a day
Circuit Killer Defense
The Sniper Attack
exitentry
exit entry
Single Adversary
The Sniper Attack
exitentry
exit entry
Anonymous Tunnel
The Sniper Attack
exitentry
exit entry
The Sniper Attack
exitentry
exit entry
DATADATA DATA
DATA
The Sniper Attack
exitentry
exit entry
DATADATA DATA
DATA
R
The Sniper Attack
exitentry
exit entry
DATADATA DATA
R
Flow Window Closed
The Sniper Attack
exitentry
exit entry
DATADATA DATA
R
R
The Sniper Attack
exitentry
exit entry
DATADATA
R
R
DATADATADATADATA
The Sniper Attack
exitentry
exit entry
DATADATA
R
R
DATADATADATA
Killed by OS
DATA