BitWhisper: Covert Thermal Signaling Between Air-Gapped Computers
Sep 30, 2026
This episode examines BitWhisper, a 2015 paper from Ben-Gurion University claiming that two air-gapped computers can exchange data using only CPU heat, with the receiving PC reading its own thermal sensors. It places the work against earlier covert channels (FM radio, ultrasound, electromagnetic and optical leakage), most of which can only leak data out, whereas this one claims half-duplex two-way signaling with no added hardware. The attack model is that malware already inside an isolated network has no way to receive commands, and the thermal link would supply one. The claimed range is 0 to 40 centimeters at 1 to 8 bits per hour, and the hosts flag the gap between "signals" and "bits" and the missing modulation and countermeasures sections in the draft. The discussion also covers the physics of workload-driven heating, the one-degree sensor resolution, and the two-room experiment setup with CPU and thermal-camera measurements. Listeners get a clear look at how far a physical side channel can be pushed, and at how narrow its practical limits are.
Interactive Visualization: BitWhisper: Covert Thermal Signaling Between Air-Gapped Computers
Sources:
1. BitWhisper: Covert Signaling Channel between Air-Gapped Computers using Thermal Manipulations — Mordechai Guri, Matan Monitz, Yisroel Mirski, Yuval Elovici, 2015
http://arxiv.org/abs/1503.07919
2. A Note on the Confinement Problem — Butler W. Lampson, 1973
https://scholar.google.com/scholar?q=A+Note+on+the+Confinement+Problem
3. AirHopper: Bridging the Air-Gap between Isolated Networks and Mobile Phones using Radio Frequencies — Mordechai Guri, Gabi Kedma, Assaf Kachlon, Yuval Elovici, 2014
https://scholar.google.com/scholar?q=AirHopper%3A+Bridging+the+Air-Gap+between+Isolated+Networks+and+Mobile+Phones+using+Radio+Frequencies
4. Ultrasonic Networking / On Covert Acoustical Mesh Networks in Air — Michael Hanspach, Michael Goetz, 2013
https://scholar.google.com/scholar?q=Ultrasonic+Networking+%2F+On+Covert+Acoustical+Mesh+Networks+in+Air
5. Air-Gap Security: Survey of Covert Channels (e.g., Air-Gap Covert Channels: A Survey and Taxonomy) — Mordechai Guri, Yuval Elovici and collaborators, 2018-2020
https://scholar.google.com/scholar?q=Air-Gap+Security%3A+Survey+of+Covert+Channels+%28e.g.%2C+Air-Gap+Covert+Channels%3A+A+Survey+and+Taxonomy%29
6. BitWhisper: Covert Signaling Channel between Air-Gapped Computers using Thermal Manipulations — Mordechai Guri, Matan Monitz, Yisroel Mirski, Yuval Elovici, 2015
https://scholar.google.com/scholar?q=BitWhisper%3A+Covert+Signaling+Channel+between+Air-Gapped+Computers+using+Thermal+Manipulations
7. Covert Channels through Thermal Emissions / Thermal Covert Channels on Multi-core Platforms — Ramya Jayaram Masti, Devendra Rai, Aanjhan Ranganathan, Christian Müller, Lothar Thiele, Srdjan Capkun, 2015
https://scholar.google.com/scholar?q=Covert+Channels+through+Thermal+Emissions+%2F+Thermal+Covert+Channels+on+Multi-core+Platforms
8. Hot Pixels / Frequency-based thermal channels (thermal side-channel work) — Various authors, 2015-2019
https://scholar.google.com/scholar?q=Hot+Pixels+%2F+Frequency-based+thermal+channels+%28thermal+side-channel+work%29
9. Stuxnet Dossier — Nicolas Falliere, Liam O Murchu, Eric Chien (Symantec), 2011
https://scholar.google.com/scholar?q=Stuxnet+Dossier
10. Exfiltration of Information from Air-Gapped Machines Using Monitor's LED Indicator / and related Guri et al. work (e.g., Air-Gap Exfiltration surveys) — Mordechai Guri, Boris Zadov, Yuval Elovici and others, 2014-2019
https://scholar.google.com/scholar?q=Exfiltration+of+Information+from+Air-Gapped+Machines+Using+Monitor%27s+LED+Indicator+%2F+and+related+Guri+et+al.+work+%28e.g.%2C+Air-Gap+Exfiltration+surveys%29
11. Data Exfiltration: A Review of External Attack Vectors and Countermeasures — Faheem Ullah, Matthew Edwards, Rajiv Ramdhany, Ruzanna Chitchyan, M. Ali Babar, Awais Rashid, 2018
https://scholar.google.com/scholar?q=Data+Exfiltration%3A+A+Review+of+External+Attack+Vectors+and+Countermeasures
12. A Mathematical Theory of Communication — Claude E. Shannon, 1948
https://scholar.google.com/scholar?q=A+Mathematical+Theory+of+Communication
13. An Introduction to Deep Learning for the Physical Layer — Timothy O'Shea, Jakob Hoydis, 2017
https://scholar.google.com/scholar?q=An+Introduction+to+Deep+Learning+for+the+Physical+Layer
14. Covert channel work on timing and protocol design (e.g., Cabuk, Brodley, Shields, 'IP Covert Timing Channels: Design and Detection') — Serdar Cabuk, Carla E. Brodley, Clay Shields, 2004
https://scholar.google.com/scholar?q=Covert+channel+work+on+timing+and+protocol+design+%28e.g.%2C+Cabuk%2C+Brodley%2C+Shields%2C+%27IP+Covert+Timing+Channels%3A+Design+and+Detection%27%29
15. Hot or Not: Revealing Hidden Services by their Clock Skew — Steven J. Murdoch, 2006
https://scholar.google.com/scholar?q=Hot+or+Not%3A+Revealing+Hidden+Services+by+their+Clock+Skew
16. On Covert Acoustical Mesh Networks in Air — Michael Hanspach, Michael Goetz, 2013
https://scholar.google.com/scholar?q=On+Covert+Acoustical+Mesh+Networks+in+Air
17. Soft Tempest: Hidden Data Transmission Using Electromagnetic Emanations — Markus G. Kuhn, Ross J. Anderson, 1998
https://scholar.google.com/scholar?q=Soft+Tempest%3A+Hidden+Data+Transmission+Using+Electromagnetic+Emanations
18. Whispers in the Hyper-space: High-speed Covert Channel Attacks in the Cloud — Zhenyu Wu, Zhang Xu, Haining Wang, 2012
https://scholar.google.com/scholar?q=Whispers+in+the+Hyper-space%3A+High-speed+Covert+Channel+Attacks+in+the+Cloud
19. Fansmitter: Acoustic Data Exfiltration from (Speakerless) Air-Gapped Computers — Mordechai Guri, Yosef Solewicz, Andrey Daidakulov, Yuval Elovici, 2016
https://scholar.google.com/scholar?q=Fansmitter%3A+Acoustic+Data+Exfiltration+from+%28Speakerless%29+Air-Gapped+Computers
20. Thermal covert channels on multi-core platforms — Ramya Jayaram Masti, Devendra Rai, Aanjhan Ranganathan, Christian Müller, Lothar Thiele, Srdjan Capkun, 2015
https://scholar.google.com/scholar?q=Thermal+covert+channels+on+multi-core+platforms
Interactive Visualization: BitWhisper: Covert Thermal Signaling Between Air-Gapped Computers
1. BitWhisper: Covert Signaling Channel between Air-Gapped Computers using Thermal Manipulations — Mordechai Guri, Matan Monitz, Yisroel Mirski, Yuval Elovici, 2015
http://arxiv.org/abs/1503.07919
2. A Note on the Confinement Problem — Butler W. Lampson, 1973
https://scholar.google.com/scholar?q=A+Note+on+the+Confinement+Problem
3. AirHopper: Bridging the Air-Gap between Isolated Networks and Mobile Phones using Radio Frequencies — Mordechai Guri, Gabi Kedma, Assaf Kachlon, Yuval Elovici, 2014
https://scholar.google.com/scholar?q=AirHopper%3A+Bridging+the+Air-Gap+between+Isolated+Networks+and+Mobile+Phones+using+Radio+Frequencies
4. Ultrasonic Networking / On Covert Acoustical Mesh Networks in Air — Michael Hanspach, Michael Goetz, 2013
https://scholar.google.com/scholar?q=Ultrasonic+Networking+%2F+On+Covert+Acoustical+Mesh+Networks+in+Air
5. Air-Gap Security: Survey of Covert Channels (e.g., Air-Gap Covert Channels: A Survey and Taxonomy) — Mordechai Guri, Yuval Elovici and collaborators, 2018-2020
https://scholar.google.com/scholar?q=Air-Gap+Security%3A+Survey+of+Covert+Channels+%28e.g.%2C+Air-Gap+Covert+Channels%3A+A+Survey+and+Taxonomy%29
6. BitWhisper: Covert Signaling Channel between Air-Gapped Computers using Thermal Manipulations — Mordechai Guri, Matan Monitz, Yisroel Mirski, Yuval Elovici, 2015
https://scholar.google.com/scholar?q=BitWhisper%3A+Covert+Signaling+Channel+between+Air-Gapped+Computers+using+Thermal+Manipulations
7. Covert Channels through Thermal Emissions / Thermal Covert Channels on Multi-core Platforms — Ramya Jayaram Masti, Devendra Rai, Aanjhan Ranganathan, Christian Müller, Lothar Thiele, Srdjan Capkun, 2015
https://scholar.google.com/scholar?q=Covert+Channels+through+Thermal+Emissions+%2F+Thermal+Covert+Channels+on+Multi-core+Platforms
8. Hot Pixels / Frequency-based thermal channels (thermal side-channel work) — Various authors, 2015-2019
https://scholar.google.com/scholar?q=Hot+Pixels+%2F+Frequency-based+thermal+channels+%28thermal+side-channel+work%29
9. Stuxnet Dossier — Nicolas Falliere, Liam O Murchu, Eric Chien (Symantec), 2011
https://scholar.google.com/scholar?q=Stuxnet+Dossier
10. Exfiltration of Information from Air-Gapped Machines Using Monitor's LED Indicator / and related Guri et al. work (e.g., Air-Gap Exfiltration surveys) — Mordechai Guri, Boris Zadov, Yuval Elovici and others, 2014-2019
https://scholar.google.com/scholar?q=Exfiltration+of+Information+from+Air-Gapped+Machines+Using+Monitor%27s+LED+Indicator+%2F+and+related+Guri+et+al.+work+%28e.g.%2C+Air-Gap+Exfiltration+surveys%29
11. Data Exfiltration: A Review of External Attack Vectors and Countermeasures — Faheem Ullah, Matthew Edwards, Rajiv Ramdhany, Ruzanna Chitchyan, M. Ali Babar, Awais Rashid, 2018
https://scholar.google.com/scholar?q=Data+Exfiltration%3A+A+Review+of+External+Attack+Vectors+and+Countermeasures
12. A Mathematical Theory of Communication — Claude E. Shannon, 1948
https://scholar.google.com/scholar?q=A+Mathematical+Theory+of+Communication
13. An Introduction to Deep Learning for the Physical Layer — Timothy O'Shea, Jakob Hoydis, 2017
https://scholar.google.com/scholar?q=An+Introduction+to+Deep+Learning+for+the+Physical+Layer
14. Covert channel work on timing and protocol design (e.g., Cabuk, Brodley, Shields, 'IP Covert Timing Channels: Design and Detection') — Serdar Cabuk, Carla E. Brodley, Clay Shields, 2004
https://scholar.google.com/scholar?q=Covert+channel+work+on+timing+and+protocol+design+%28e.g.%2C+Cabuk%2C+Brodley%2C+Shields%2C+%27IP+Covert+Timing+Channels%3A+Design+and+Detection%27%29
15. Hot or Not: Revealing Hidden Services by their Clock Skew — Steven J. Murdoch, 2006
https://scholar.google.com/scholar?q=Hot+or+Not%3A+Revealing+Hidden+Services+by+their+Clock+Skew
16. On Covert Acoustical Mesh Networks in Air — Michael Hanspach, Michael Goetz, 2013
https://scholar.google.com/scholar?q=On+Covert+Acoustical+Mesh+Networks+in+Air
17. Soft Tempest: Hidden Data Transmission Using Electromagnetic Emanations — Markus G. Kuhn, Ross J. Anderson, 1998
https://scholar.google.com/scholar?q=Soft+Tempest%3A+Hidden+Data+Transmission+Using+Electromagnetic+Emanations
18. Whispers in the Hyper-space: High-speed Covert Channel Attacks in the Cloud — Zhenyu Wu, Zhang Xu, Haining Wang, 2012
https://scholar.google.com/scholar?q=Whispers+in+the+Hyper-space%3A+High-speed+Covert+Channel+Attacks+in+the+Cloud
19. Fansmitter: Acoustic Data Exfiltration from (Speakerless) Air-Gapped Computers — Mordechai Guri, Yosef Solewicz, Andrey Daidakulov, Yuval Elovici, 2016
https://scholar.google.com/scholar?q=Fansmitter%3A+Acoustic+Data+Exfiltration+from+%28Speakerless%29+Air-Gapped+Computers
20. Thermal covert channels on multi-core platforms — Ramya Jayaram Masti, Devendra Rai, Aanjhan Ranganathan, Christian Müller, Lothar Thiele, Srdjan Capkun, 2015
https://scholar.google.com/scholar?q=Thermal+covert+channels+on+multi-core+platforms
Interactive Visualization: BitWhisper: Covert Thermal Signaling Between Air-Gapped Computers