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PHY Covert Channels:
Can you see the Idles?
Ki Suh Lee
Cornell University
첩
자
Chupja
Joint work with Han Wang, and Hakim Weatherspoon
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첩자 (chupja)
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Network Covert Channels
• Hiding information
– Through communication not intended for data transfer
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Network Covert Channels
• Hiding information
– Through communication not intended for data transfer
– Using legitimate packets (Overt channel)
• Storage Channels: Packet headers
• Timing Channels: Arrival times of packets
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Network Covert Channels
• Hiding information
– Through communication not intended for data transfer
– Using legitimate packets (Overt channel)
• Storage Channels: Packet headers
• Timing Channels: Arrival times of packets
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Goals of Covert Channels
• Bandwidth
– How much information can be delivered in a second
• Robustness
– How much information can be delivered without loss / error
• Undetectability
– How well communication is hidden
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Goals of Covert Channels
• Bandwidth
– How much information can be delivered in a second
– 10~100s bits per second
• Robustness
– How much information can be delivered without loss / error
Application
– Cabuk’04, Shah’06
• Undetectability
– How well communication is hidden
– Liu’09, Liu’10
Transport
Network
Data Link
Physical
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Current network covert channels
are implemented in L3~4 (TCP/IP) layers
and are extremely slow.
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Chupja: PHY Covert Channel
• Bandwidth
– How much information can be delivered in a second
– 10~100s bits per second -> 10s~100s Kilo bits per second
• Robustness
– How much information can be delivered without loss / error
Application
– Bit Error Rate < 10%
• Undetectability
– How well communication is hidden
– Invisible to detection software
Transport
Network
Data Link
Physical
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Chupja is a network covert channel
which is faster than priori art.
It is implemented in L1 (PHY),
robust and virtually invisible to software.
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Outline
•
•
•
•
Introduction
Design
Evaluation
Conclusion
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Outline
• Introduction
• Design
– Threat Model
– 10 Gigabit Ethernet
• Evaluation
• Conclusion
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Threat Model
Application
Transport
Network
Data Link
Passive
Adversary
Commodity Server
Commodity NIC
Application
Transport
Network
Data Link
Physical
Physical
Sender
Receiver
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10 Gigabit Ethernet
• Idle Characters (/I/)
Application
Transport
Packet i
Packet i+1
Packet i+2
Network
Data Link
–
–
–
–
Each bit is ~100 picosecond wide
7~8 bit special character in the physical layer
700~800 picoseconds to transmit
Only in PHY
Physical
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Terminology
• Interpacket delays (D) and gaps (G)
IPG
Packet i
Packet i+1
IPD
• Homogeneous packet stream
Packet i
Packet i+1
Packet i+2
– Same packet size,
– Same IPD (IPG),
– Same destination
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Chupja: Design
• Homogeneous stream
G
Packet i
IPG
G
Packet i+1
D
• Sender
IPG
D
G-Ɛ
Packet i
• Receiver
‘0’
G+Ɛ
Packet i+1
D-Ɛ
‘1’
Di
Packet i+2
D+Ɛ
Gi
Packet i
Packet i+2
‘0’
Gi+1
Packet i+1
‘1’
Packet i+2
Di+1
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Chupja: Design
• With shared G
– Encoding ‘1’: Gi = G + ε
– Encoding ‘0’: Gi = G - ε
G-Ɛ
Packet i
D-Ɛ
‘0’
G+Ɛ
Packet i+1
‘1’
Packet i+2
D+Ɛ
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Implementation
• SoNIC [NSDI ’13]
– Software-defined Network Interface Card
– Allows control and access every bit of PHY
• In realtime, and in software
Application
Transport
Network
Data Link
Physical
• 50 lines of C code addition
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Outline
• Introduction
• Design
• Evaluation
– Bandwidth
– Robustness
– Undetectability
• Conclusion
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Evaluation
• What is the bandwidth of Chupja?
• How robust is Chupja?
– Why is Chupja robust?
• How undetectable is Chupja?
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What is the bandwidth of Chupja?
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Evaluation: Bandwidth
• Covert bandwidth equals to packet rate of overt channel
Covert Channel Capacity (bps)
1.E+08
1.E+07
1.E+06
1.E+05
1.E+04
1518B 1Gbps
81kbps
1.E+03
1.E+02
0.01
64B
512B
1024B
1518B
0.1
0.5
1
3
6
Overt Channel Throughput (Gbps)
9
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How robust is Chupja?
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Evaluation Setup
• Small Network
• National Lambda Rail
– Six commercial switches
– Average RTT: 0.154 ms
SW1
SW2
– Nine routing hops
– Average RTT: 67.6ms
– 1~2 Gbps External Traffic
Chicaco
SW1
Boston
Cleveland
SW2
SW3
SW4
Sender
Receiver
Cornell (NYC)
Sender
NLR (NYC)
Receiver
Cornell (Ithaca)
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Evaluation: Robustness
• Overt Channel at 1 Gbps (D = 12211ns, G=13738 /I/s)
• Covert Channel at 81 kbps
0.6
Small No Ext.
Small Ext 3.6G
NLR
0.5
BER
0.4
0.3
8.9%
0.2
7.7%
0.1
2.8%
0
16
32
64
128
256 512 1024 2048 4096
Ɛ (/I/s)
?
Sender
Receiver
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Evaluation: Robustness
• Overt Channel at 1 Gbps (D = 12211ns, G=13738 /I/s)
• Covert Channel at 81 kbps
• Modulating IPGS at 1.6us scale (=2048 /I/s)
0.6
Small No Ext.
Small Ext 3.6G
NLR
0.5
BER
0.4
0.3
8.9%
0.2
7.7%
0.1
2.8%
0
16
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64
128
256 512 1024 2048 4096
Ɛ (/I/s)
?
Sender
Receiver
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Why is Chupja robust?
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Evaluation: Why?
• Switches do not add significant perturbations to IPDs
• Switches treat ‘1’s and ‘0’s as uncorrelated
– Over multiple hops when there is no external traffic.
– With external traffic
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Evaluation: Why?
• Switches do not add significant perturbations to IPDs
• Switches treat ‘1’s and ‘0’s as uncorrelated
– Over multiple hops when there is no external traffic.
– With external traffic
Homogeneous
1518B at 1 Gbps
Sender
Chupja (Ɛ = 256/I/s)
1518B at 1 Gbps
Receiver
Sender
Receiver
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Evaluation: Why?
• Switches do not add significant perturbations to IPDs
• Switches treat encoded ‘0’ and ‘1’ as uncorrelated
– Over multiple hops when there is no external traffic.
1.
1.
15
12
1 hop
3
6
9
0.1
0.01
90% in
D ± 100ns
250ns
D+Ɛ
0.01
0.001
0.001
0.0001
0.0001
0.00001
0.00001
0.000001
11343.51515
12
15
1 hop
3
6
9
90% in
0.1
D
D –- Ɛ ± 250ns
100ns
D-Ɛ
12211.2
13078.88485
0.000001
11343.51515
12211.2
Interpacket Delay (ns)
Interpacket Delayy (ns)
Homogeneous stream
Chupja stream ( Ɛ=256/I/s )
13078.88485
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Evaluation: Why?
• Most of IPDs are within some range from original IPD
– Even when there is external traffic.
Ɛ (/I/s)
(ns)
256
(=204.8ns)
512
(=409.6)
1024
(=819.2)
2048
(=1638.4)
4096
(=3276.8)
BER
0.367
0.391
0.281
0.089
0.013
Encoded
‘Zero’
Boston
Encoded ‘One’
Chicaco
Cleveland
Cornell (NYC)
NLR (NYC)
Cornell (Ithaca)
Sender
Receiver
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Evaluation: Why?
• Switches do not add significant perturbations to IPDs
• Switches treat ‘1’s and ‘0’s as uncorrelated
– Over multiple hops when there is no external traffic.
– With external traffic
With sufficiently large Ɛ,
the interpacket spacing holds throughout
the network, and BER is less than 10%
1518B at 1 Gbps
Sender
?
Receiver
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How undetectable is Chupja?
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Evaluation: Detection Setup
• Commodity server with 10G NIC
– Kernel timestamping
Kernel
timestamping
SoNIC
timestamping
NLR
Sender
NLR
Receiver
Sender
Receiver
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Evaluation: Detection
• Adversary cannot detect patterns of Chupja
1.
1.
HOM
0.1
1024
Ɛ = 1024
0.01
4096
Ɛ = 4096
0.001
Ɛ = 1024
1024
0.01
Ɛ = 4096
4096
0.001
0.0001
0.0001
0.00001
1228
HOM
0.1
0.00001
12211
Interpacket Delay (ns)
Kernel Timestamping
23194
0.000001
1228
12211
Interpacket Delay (ns)
23194
SoNIC Timestamping
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Evaluation: Summary
• What is the bandwidth of Chupja?
– 10s~100s Kilo bits per second
• How robust is Chupja?
– BER < 10% over NLR
– Why is Chupja robust?
• Sufficiently large Ɛ holds throughout the network
• How undetectable is Chupja?
– Invisible to software
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Conclusion
• Chupja: PHY covert channel
– High-bandwidth, robust, and undetectable
• Based on understanding of network devices
– Perturbations from switches
– Inaccurate endhost timestamping
첩
자
• http://sonic.cs.cornell.edu & GENI (ExoGENI)!!!
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Thank you
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