- 1 Introduction
- 2 MAC Spoofing Warning
- 3 Other Location Tracking Risks
- 4 MAC Spoofing on Different Networks
- 5 Changing MAC Addresses
- 6 References
- 7 License
All network cards, both wired and wireless, have a unique identifier called a MAC address.  MAC addresses are stored in hardware and are used to assign an address to computers on the local network.
The MAC address is normally not traceable because it is not passively sent to computers beyond the local router.  However, other computers on the local network can potentially log it, which would then provide proof the user's computer connected to that specific network. If users intend to use an untrusted, public network then MAC spoofing should be considered. 
MAC Spoofing Warning
Apart from the difficulty in creating an appropriate MAC address for spoofing purposes, there are also technical hurdles to overcome in the form of preventing automatic network connections.
It is futile to prepare a spoofed MAC address if the computer instantly connects to the public network after booting, disclosing the user's real MAC address in the process:
- Physical Isolation: Whonix-Gateway ™ automatically connects to Tor after start.
- USB Wi-FI Device: Automatic connections might also occur, depending on the configuration.
- VM users: The host operating system most likely automatically connects via updates, perhaps time sync, and other avenues.
Burner Wi-Fi USB Sticks
One immediate workaround for the Wi-Fi card profiling threat is to buy new "burner" Wi-Fi USB sticks from different manufacturers. Take care to disable the computer's native Wi-Fi functionality in the BIOS settings if pursuing this option -- the computer's characteristics will have likely been logged if it was ever used from an untrusted hotspot. Burner devices should only be enabled for connectivity at the intended public destination. If this advice is ignored and burner devices are used for network connections at locations tied to or regularly visited by the user, this can lead to deanonymization. A different burner stick should be used for each new location to avoid geographical profiling / tracking.
Random MAC Addresses
The problem with using a random MAC address is that the chosen vendor ID may be non-existent. Even if it exists, it is possible to end up with a vendor ID which has either never been used or not for decades. When spoofing MAC addresses, it is critical to use a a popular vendor ID. The initial, second part of the MAC address can safely be random or unique. 
Research on this issue is still ongoing. At present, Whonix ™ cannot provide detailed instructions on how to create appropriate MAC addresses fulfilling the criteria above.
Other Location Tracking Risks
Authentication Fingerprinting Techniques
An authentication technique can fingerprint devices by observing inter-packet timings on a LAN's wire-segment; one side effect is that user devices can be tracked. The timing effects are the result of how various components in a machine create packets.  Fortunately, this technique cannot be used to identify devices across the Internet. 
This technique can be defeated by inducing random delays in a machine's packet stream. Since there is no problem with impersonating other devices on the LAN, it does not matter that such an authentication system will view these machines as "unknown".  Note also that spectrum analyzers have been used to fingerprint the unique electromagnetic (EM) characteristics of a Wi-Fi card. The disposable USB Wi-Fi workaround described further above would mitigate this attack. 
Tor Entry Guard Fingerprinting
Dealing with the MAC address problem is only one piece of the larger location tracking puzzle. Users must also contend with changing the usual Tor entry guards used for connections across different locations, in order to prevent guard fingerprinting. To mitigate this threat, follow one of the recommended configurations:
- Clone Whonix-Gateway ™ (sys-whonix) with New Entry Guards.
- Regenerate the Tor State File after Saving the Current Tor State.
- Configure Tor to use Alternating Bridges.
- If moving to a new location permanently, create Fresh Tor Entry Guards by Regenerating the Tor State File.
To fully thwart this threat, entry guard changes are necessary for every Tor instance on the user's machine host (apt-transport-tor) and guest.
MAC Spoofing on Different Networks
If the user's home network has a cable modem internet connection, the ISP either provides the cable modem device as part of the service or requires pre-registration of the MAC address of the self-provided cable modem in order to setup the service.
If a user manages to hack or change the MAC address of the modem, the service would immediately cease functioning because the IP address assignment is apportioned for, and bound to, that specific MAC address. As a result, when connecting from behind a cable modem/NAT router, MAC address spoofing of the computer's ethernet adapter may be pointless. If a user is traced, the trackable endpoint will be the MAC address of the cable modem device.
The MAC address should not be changed in this scenario, otherwise it may bring undesired administrator attention to the service/user and/or simply prevent access to the Internet.
Using Personal Computers in a Public Network
In this scenario, the MAC address must be changed and a new set of Tor entry guards should also be configured.  Attempts should be made to disguise the use of Tor from the administrator of the public network. Depending on the user's configuration, this may involve using an obfsproxy bridge or the tunneling of traffic through SSH or a VPN prior to connecting to the Tor network.
Depending on the user's threat model, changing the MAC address and using Tor might rule out revisiting that public network again in the future. If the same public network will be reused, then it is necessary to decide whether to use the same MAC address (and set of Tor entry guards) or to generate a new one.
If MAC address logging by the administrator is suspected, it is unwise to change the MAC address and arouse suspicion. If it is assessed the network is sufficiently public and observation is unlikely, then it might be safe to use a new MAC address -- with a popular vendor ID and random/unique second part (identifier) -- each time the network is used.
For further discussion on this rather complex topic, see Dev/MAC.
Changing MAC Addresses
If you are interested in MAC address spoofing in Non-Qubes-Whonix ™, please press on Expand on the right.
Qubes users can manually change MAC addresses in the NetVM by following either the Network Manager or macchanger guides. MAC Address Randomization capability for Wi-Fi has been implemented, but it is not applied by default.
Refer to the following Qubes documentation and related support items for further information and advice:
- Qubes documentation: Anonymizing your MAC Address
- Qubes-Users forum: Instructions for Installing Macchanger Needed
- Explore local network privacy solutions beyond MAC address randomization
The following steps spoof the MAC address in Windows 10 via Device Manager: 
Windows Key + X.
- Expand the list of network adapters.
- Right-click the appropriate adapter.
- Navigate to
- Enter any 12 digit hexadecimal value.
Reboot the computer for the changes to take effect. To check the changes are functional, in a terminal run.
The physical address of the adapter should show a new MAC address.
See footnote. 
- Unless the computer is infected with malware designed to disclose this identifier.
- Why MAC Address Randomization is not Enough: An Analysis of Wi-Fi Network Discovery Mechanisms
- Also note that if MAC address changing is always enabled, it might cause connectivity problems on some networks.
- A Passive Technique for Fingerprinting Wireless Devices with Wired-side Observations
- The primary weakness of this technique is that it relies on fine-grained packet timing; timing that is lost as a result of buffering in switches and routers. Therefore, this technique and similar methods are not suited for identification across the Internet. Rather, it is perfectly suited for the significant challenge of local network access control and other local network activities like counterfeit detection.
- Figure 7(a) shows attackers that can vary their packet sizes, change their data rate, and tunnel their packets through another protocol. Figure 7(b) presents attackers that can introduce constant or random delays to the packet stream and load the CPU with intensive applications to overshadow normal behavior. Figure 7(c) shows an attacker that can modify or change its operating system. GTID (the passive fingerprinting method) detects these attacks and classifies all of these devices that generated attack traffic from previously seen devices as unknown.
- There have also been physical layer approaches to fingerprinting wireless devices. Radio frequency (RF) emitter fingerprinting uses the distinct EM characteristics that arise from differences in circuit topology and manufacturing tolerances. This approach has a history of use in cellular systems and has more recently been applied to Wi-Fi and Bluetooth emitters. The EM properties fingerprint the unique transmitter of a signal and these differ from emitter to emitter. This technique requires expensive signal analyzer hardware to be within RF range of the target.
- This process involves removal of the /var/lib/tor/state file.
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