Wavecatcher - acoustic cryptanalysis board

A simple device to perform acoustic cryptanalysis

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The project will be used for acoustic cryptanalysis - "Acoustic cryptanalysis is a type of side channel attack that exploits sounds emitted by computers or other devices".

A number of aspects of computers emit ultrasound including SMPSs to inductors and capacitors present on the computer's motherboard itself.

I will be using an STM32 ARM Microcontroller and the SPH0641LU4H-1 MEMS microphone. These microphones are capable of reaching ultrasonic frequencies of around 80kHz. They produce a Pulse Density Modulation output, which means they output a binary signal, which we will be able to decode on the microcontroller itself and present the decoded signal to a computer via USB.

I am currently deciding the number of MEMS microphones to use.


The project has a goal of creating a simple USB ultrasound microphone capable of receiving up to 80kHz. 

As one of the primary goals is enabling you to perform 'acoustic cryptanalysis', a simple software program will be created enabling potentially interesting signals to monitored and decoded.

For example data may be 'exfiltrated' from a SMPS of a computer, by causing the processor to draw high or low amounts of power, causing the ultrasound emitted from the SMPS to change.  The signal from the SMPS will then be decodable by our software.


This schematic depicts an STM32 microcontroller along with the MEMS ultrasound microphone.  It is powered and accessible by USB.   You will notice there is a 6 pin header to program the microcontroller.


The following image depicts the current positions of the components in kicad, before I've routed them.

I'm quite new to pcb design, especially with a microcontroller with so many pins!  So I'm going to spend a while positioning the components until I'm happy with their location prior to routing.

The routed PCB looks as follows:

I just sent it off to MacroFab for a prototype to be created today (16th April), hopefully I've not made any mistakes!

  • 1 × STM32F302RBT Microcontroller
  • 1 × SPH0641LU4H-1 MEMS microphone
  • 1 × LP38693MP-3.3 Power Management ICs / Linear Voltage Regulators and LDOs

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