Hi, I’m Youngwook and I’m Sid. We are happy to be here to present our work, Bit Whisperer:
Enabling Ad-hoc, Short-range, Walk-Up-and-Share Data Transmissions via Surface-restricted Acoustics.
This work was done in collaboration with Zhouyu Li, Steven Craig,
Phoebe Welch, Chengzhi Shi, Thad Starner, and my advisors Gregory Abowd and Sauvik Das.
In the physical world, when you want to share a secret with people nearby, what do you do?
You make sure no one else is around, you lean in, and whisper.
But, in the digital world, sharing a secret with people nearby looks quite different.
Existing solutions for secure, short-range wireless communication like Bluetooth require device pairing,
which can be inconvenient for a number of everyday sharing tasks
that require both ease-of-use and “good enough” security such as
sharing contact information with conference attendees, secure link sharing in a coffee-shop meeting, etc.
Also, because of the invisibility and abstractness of wireless data transfer protocols,
there is no easy way for end-users to ensure who may eavesdrop on their data transfer.
These challenges brought us to the questions.
What if we can design digital whispering that limits the scope of wireless digital communication
to a visible, physical medium while enabling simple and ad-hoc interactions we call “walk up-and-share” interactions?
Can we design such a system without any specialized devices or objects? Is this possible?
We introduce Bit Whisperer, a novel ad-hoc, short-range, wireless communication system that enables “digital whispering”.
The key insight of Bit Whisperer is wireless data transfer is physically constrained to nearby devices
co-located on a solid surface like a table surface.
That means only devices that are co-located on the physical surface can share data
while a malicious actor’s devices that are not on the surface cannot eavesdrop on the surface-restricted data transfer.
As shown in this video, once a transmitter transfers data, the receiver device that is
co-located on the same surface successfully receives the data while the receiver that is not co-located fails to receive it.
Let me talk about Bit Whisperer’s operation principle.
We leverage two physical properties of sound to design Bit Whisperer.
First, sound attenuates over long distances, meaning that devices that are closer are more likely to hear whispers.
Second, sound is reflected from rigid physical surfaces.
With that, we hypothesized that a digital whisper transmitted on a solid table would be more clear and audible
for devices that are physically on the same table than for devices that are not.
In order to verify this hypothesis, we ran a simulation on a software simulation tool
to evaluate how sound propagation differs above a table surface.
We simulated two setups:
On-table setup where a transmitter device and a receiver device are co-located on a flat surface;
And off-table setup where a transmitter and a receiver device are placed on separate, air-gapped surfaces
From the simulation, we found that the on-table receiver received almost twice as much acoustic pressure
as the air-gapped receiver because of the sound reflection from the surface.
Next, we empirically verified the simulated tests
by running a white noise test in a lab setup
We used a transmitter device to play white noise and a receiver device to record the noise.
We verified that the on-table receiver receives a stronger acoustic signal
than the off-table receiver over the 18 to 22 kilohertz range.
Let me talk about how to implement Bit Whisperer. There are three key components for the implementation.
First, we use inaudible and minimally perceptible acoustic signals
between 18 kilohertz and 20 kilohertz that can be generated by commodity devices
Next, inspired by prior work, we used Frequency-shift Keying method for data communication and evaluated
20 frequency channels within the frequency range.
Then, among 20 channels,
we found 8 usable channels for 8-bit ASCII character data transfer of Bit Whisperer.
Lastly, any lossy communication channel must account for transmission error
and we want legitimate receivers to accurately recover lossy messages
while preventing adversarial receivers from doing the same.
We accomplished this with a combination of Forward Error Correction (FEC) and encryption.
The forward error correction scheme is commonly used to recover the lossy data.
But, if there is a limited amount of error to be corrected, too lossy data cannot be corrected.
We use this property.
As a receiver can receive stronger acoustic signals on the table than off the table,
it’d be likely that an adversary who would be off the table would receive lossier data
than a legitimate user who would place their device on the table.
This way, legitimate users can transfer the corrected data while a malicious actor cannot recover the lossy data.
However, it may not be necessary for an adversary device to detect and correct all errors.
Even if the intercepted message is 70% accurate, for example Jo_n D_e instead of John Doe,
that may be good enough for many adversarial purposes.
To address this issue, we use the encryption scheme.
This way, if the adversary receives even one erroneous bit of the encrypted raw data,
they will not be able to recover any of the plaintext.
To evaluate if it was effective, we wanted to answer these two questions:
How robust and accurate is data transmission under Bit Whisperer for legitimate use cases?
And how secure is Bit Whisperer against nearby eavesdroppers?
To do so, we examined data transmissions of two setups:
the on-table setup that represents legitimate users’ data transfer
and the off-table setup that represents an adversary who tries to access the on-table data transfer.
We ran an evaluation with a wide range of parameters to replicate the Bit Whisperer’s data communication environments.
Overall, results indicate that the further distance and wider angular displacement between a transmitter and a receiver,
the bigger data transmission success rate difference between the on-table and off-table setups Bit Whisperer can achieve.
We found that if an adversary attempts to access a legitimate user's data transfer at 1m away
and 60 degree to 90 degree angular displacement, legitimate users can securely transfer their data with Bit Whisperer.
Please check our paper for more detail
We demonstrate three example applications.
First, users can use Bit Whisperer for 1-to-1 data sharing like Contact Sharing.
As shown here, two people can share their contact information at a coffee shop.
Bit Whisperer is not limited to one-to-one data sharing.
Bit Whisperer also allows 1-to-N data sharing as well.
So, users can use Bit Whisperer to share a secret group chat link among a group of two or more users.
Similarly, a user can use an authenticated device to unlock other devices that are placed on the same surface at once.
As you've seen in these applications, Bit Whisperer can be deployed by repurposing an everyday material surface
without any specialized hardware while enabling ad-hoc, secure communication.
In summary, we implemented and evaluated Bit Whisperer,
a novel acoustic-based ad-hoc, short-range, wireless communication protocol that enables ‘digital whispering’.
That’s all for our talk. Thank you so much.