feature article
Subscribe Now

Hacking a Secure Air-Gapped Computer

Research Team Finds Novel Ways to Bypass Security

Some security weaknesses would be hilarious if they weren’t so serious. And one man and his crack research team have found dozens of surprising ways to crack seemingly impenetrable computers. You’ve got to give them points for originality. 

There are a lot of ways to secure a computer, depending on what you’re trying to prevent. Do you want to keep secure information inside? Do you want to prevent outside malware from getting in? Do you want to limit access to only the right people? The list goes on. 

“Air gapping” is the gold standard for trapping sensitive information inside a computer and making sure it can’t be shared, transmitted, or go walkabout. An air-gapped computer has no CD-ROM burner, no floppy disk drive, no SD card interface, no USB slots, and no network interface of any kind. That means no Ethernet, no Wi-Fi, no Bluetooth – nothing that could potentially be used to send data outside the machine. 

Seems pretty secure, right? With no network and no place to stick removable media, there is physically no way to get data off of the computer. Or so you’d think. But Mordechai Guri and his merry band of helpers at Ben-Gurion University of the Negev in Israel has found a way. Many ways, in fact, and some are truly surprising. Or demoralizing, depending on your job description. 

The latest installment in their oeuvre is nicknamed Air-Fi, and it MacGyvers a Wi-Fi interface out of hardware that’s already in your PC. It relies on the underlying electromagnetic radiation that results from any signal transmitted over a wire. Specifically, it subverts your computer’s DRAM into wiggling the memory bus at 2.4 GHz – exactly the frequency range of the 802.11b/g/n Wi-Fi standards. And, since most computers today use standard DIMMs, the hardware is readily available, and you’re pretty much hosed. 

If you want to know how it works, or even to try it out for yourself, the detailed description is in his research paper. It even provides pseudocode. 

Since Air-Fi mimics Wi-Fi, anything in the area with a Wi-Fi interface can pick up the exfiltrated data, including cellphones, wireless routers, access points, harmless IoT gadgets, or other computers. 

If you’ve assembled a new PC lately, you know that DDR4-2400 memory sticks are common. As the name suggests, these operate at a constant 2400 MHz, with memory addresses and data synchronized to the edges of the clock. That frequency sits right on top of the Wi-Fi band, so Guri and his team used this convenient (inconvenient?) parallel as the basis for their hack. The DRAM clock provides the carrier frequency, and data transactions modulate it to encode data. 

To transmit a “1” bit, the software performs a flurry of memory transactions by moving a few megabytes of arbitrary data in order to generate sufficient activity on the SDRAM bus. (CPU-to-memory transactions are a lot faster than Wi-Fi bit times, hence the large block size.) To send a “0” the software does nothing and waits. Timing loops space out the transactions to match the timing specified by Wi-Fi standard. 

Clever, but what if your computer doesn’t use DDR4-2400 memory? Surely Air-Fi won’t work with faster or slower memories, will it? Turns out, it does. 

Guri and his team experimented with both DDR3-2133 and DDR3-1600 DIMMs and successfully compromised them as well. In both cases, they overclocked the memory interface, which is very doable on most systems. Once they got the slower DIMMs running at the correct 2400-MHz rate, the rest was cake. 

For extra credit, Guri and his team also tried single-core versus multicore versions of the attack. Although Air-Fi works just fine as a single thread on a single-core system, going multicore works even better. By synchronizing the individual program threads, they were able to boost the signal strength, increase range, and lower the error rate. 

And the error rate is already pretty good, considering this isn’t even a real Wi-Fi interface. Guri’s team measured bit error rates (BER) of zero out to a range of a meter or two (depending on the computer), increasing into single-digit percentages at longer range. Signal-to-noise ratio (SNR) varied from 3 dB up to 20 dB. Not bad for a fake transmitter that’s not supposed to be there. 

At about 100 bits/sec, Air-Fi isn’t fast, but it is effective. It requires nothing unusual in terms of hardware, although it does require malware on the transmitting side. But once inside, such malware would be hard to identify because all it’s doing is memory transactions, and what’s suspicious about that? How would you detect it? Guri suggests hardware fixes like radio jamming, shielding, or physical distance from any and all potential Wi-Fi receivers.  

As inventive as Air-Fi is, I’m more impressed by some of the team’s other discoveries/inventions. For example, they’ve found ways to toggle the LEDs on your computer’s keyboard, disk drives, or network gear to exfiltrate data. Or to use the speaker. Or the fans. Or even heat. We might as well give up now. 

One thought on “Hacking a Secure Air-Gapped Computer”

Leave a Reply

featured blogs
Feb 26, 2021
OMG! Three 32-bit processor cores each running at 300 MHz, each with its own floating-point unit (FPU), and each with more memory than you than throw a stick at!...
Feb 26, 2021
In the SPECTRE 20.1 base release, we released Spectre® XDP-HB as part of the new Spectre X-RF simulation technology. Spectre XDP-HB uses a highly distributed multi-machine multi-core simulation... [[ Click on the title to access the full blog on the Cadence Community si...
Feb 24, 2021
mmWave applications are all the rage. Why? Simply put, the 5G tidal wave is coming. Also, ADAS systems use 24 GHz for SRR applications and 77 GHz for LRR applications. Obviously, the world needs mmWave tech! Traditional mmWave technology spans the 30 – 300 GHz frequency...

featured video

Designing your own Processor with ASIP Designer

Sponsored by Synopsys

Designing your own processor is time-consuming and resource intensive, and it used to be limited to a few experts. But Synopsys’ ASIP Designer tool allows you to design your own specialized processor within your deadline and budget. Watch this video to learn more.

Click here for more information

featured paper

Using the DS28E18, The Basics

Sponsored by Maxim Integrated

This application note goes over the basics of using the DS28E18 1-Wire® to I2C/SPI Bridge with Command Sequencer and discusses the steps to get it up and running quickly. It then shows how to use the device with two different devices. The first device is an I2C humidity/temperature sensor and the second one is an SPI temperature sensor device. It concludes with detailed logs of each command.

Click here to download the whitepaper

Featured Chalk Talk

General Port Protection

Sponsored by Mouser Electronics and Littelfuse

In today’s complex designs, port protection can be a challenge. High-speed data, low-speed data, and power ports need protection from ESD, power faults, and more. In this episode of Chalk Talk, Amelia Dalton chats with Todd Phillips from Littelfuse about port protection for your next system design.

Click here for more information about port protection from Littelfuse.