Computer generated acoustic field generation
Often turning on the computer, we hear a faint squeak. If it is a rarity for a laptop, then for a stationary computer, a beep can be heard even against the background of fan operation. This squeak has a dual nature. One source of squeaking is the operation of inverters of the power supply converter of the processor, the other work of its dynamic load - the processor. And if the squeak is not always heard, then we should not calm down. He is present. Only in the inaudible human ear ultrasound. This side of the phenomenon and used Adi Shamir.
In the article "Removing the RSA key by acoustic cryptanalysis with a low sampling rate" Adi Shamir and her review by Anatoly Alizar showed the possibility of recording the acoustic field created by a laptop at distances from 0.3 to 4 m. Despite the fact that quite sensitive microphones are used, speaks of a fairly high power acoustic field. It is great even for a laptop whose processor has a power consumption of less than 35 watts.
Why am I writing about the power consumed by the processor?
Back in 2002, I showed that the power of interference generated by a processor can reach up to 50% of the power consumed by a processor, depending on the filtering efficiency of the processor’s power distribution system. This power generated by the processor has an electromagnetic nature, but part of it is converted into acoustic noise on the filter elements. The other is radiated into the surrounding space in the form of electromagnetic radiation.
The frequency range of the electromagnetic field (depending on the efficiency of the filters) extends from units of hertz to hundreds of megahertz. similarly, the frequency range of the generated acoustic field (which is limited only by the emissivity of the elements).
The acoustic field is generated using electromagnetic (Ampere's law) and electrostatic forces (Lorentz's law) that exist in open space. In the presence of ferromagnetic materials in the structure, the magnetostriction effect is additionally manifested, and in the presence of ceramic capacitors, dielectrics of which have a piezoelectric effect - a piezoelectric effect. The latter multiply the conversion of the electromagnetic field into the acoustic one.
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The electromagnetic force acting on a conductor with a current in a magnetic field and located perpendicular to the direction of the field is equal to the product of the current I, the magnetic induction B and the length of the conductor.
Sometimes the Lorentz force refers to the force acting on the charge q moving at a speed v only from the magnetic field, often the total force from the electromagnetic field in general, in other words, from the electric E and magnetic B fields.
or for a capacitor
The ampere force generated by the impulse current flowing through the free turns of the inductors (and the current-carrying conductors) induces them to vibrations, which are multiplied by their (and their surrounding elements) mechanical resonance. In a computer, these are the inductances of the power system, the current through which is modulated by the current supplying the processor. It also increases if the ferrite core of such a coil has the effect of magnetostriction.
But the main source of acoustic radiation in computers (processors) are SMD ceramic capacitors, which are located on a set of the processor and the motherboard and are included in the processor power supply circuit. They are intended to filter the supply voltage from the wideband interference generated by the processor in the power bus.
To obtain their high capacitance (0.1-100 microfarads), these capacitors are made of multi-layer capacitors and, of the dielectrics of classes II and III, have a significantly higher dielectric constant and, therefore, capacitance. They are piezoelectric, therefore, a mechanical effect on them produces voltage, that is, they are subject to a microphone effect. And vice versa, when an alternating voltage is applied to them, they tend to convert it into vibrations and, accordingly, an acoustic wave. And the more layers (the greater the capacity) of such a capacitor, the greater the amplitude of the acoustic wave. These effects do not affect the operation of most power sources, unless the operating frequency is in the audio range.
The voltage filtered by them is applied to the plates of multilayer ceramic SMD capacitors, where the variable component of the voltage creates an acoustic wave.
You can reduce the power of a computer-generated acoustic field and, accordingly, the probability of extracting encryption keys:
But this is more true of computer hardware manufacturers and programmers, but for now we only have to put the computer on the vibration-absorbing surfaces, look around more often and not connect incomprehensible gadgets to the computer.
In the article "Removing the RSA key by acoustic cryptanalysis with a low sampling rate" Adi Shamir and her review by Anatoly Alizar showed the possibility of recording the acoustic field created by a laptop at distances from 0.3 to 4 m. Despite the fact that quite sensitive microphones are used, speaks of a fairly high power acoustic field. It is great even for a laptop whose processor has a power consumption of less than 35 watts.
Why am I writing about the power consumed by the processor?
Back in 2002, I showed that the power of interference generated by a processor can reach up to 50% of the power consumed by a processor, depending on the filtering efficiency of the processor’s power distribution system. This power generated by the processor has an electromagnetic nature, but part of it is converted into acoustic noise on the filter elements. The other is radiated into the surrounding space in the form of electromagnetic radiation.
The frequency range of the electromagnetic field (depending on the efficiency of the filters) extends from units of hertz to hundreds of megahertz. similarly, the frequency range of the generated acoustic field (which is limited only by the emissivity of the elements).
Mechanism of generation of acoustic field by computer
The acoustic field is generated using electromagnetic (Ampere's law) and electrostatic forces (Lorentz's law) that exist in open space. In the presence of ferromagnetic materials in the structure, the magnetostriction effect is additionally manifested, and in the presence of ceramic capacitors, dielectrics of which have a piezoelectric effect - a piezoelectric effect. The latter multiply the conversion of the electromagnetic field into the acoustic one.
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Ampere Force
The electromagnetic force acting on a conductor with a current in a magnetic field and located perpendicular to the direction of the field is equal to the product of the current I, the magnetic induction B and the length of the conductor.
F = IBl
Lorenz force
Sometimes the Lorentz force refers to the force acting on the charge q moving at a speed v only from the magnetic field, often the total force from the electromagnetic field in general, in other words, from the electric E and magnetic B fields.
F = q [E + (v ∙ B)]
or for a capacitor
F = qE
The ampere force generated by the impulse current flowing through the free turns of the inductors (and the current-carrying conductors) induces them to vibrations, which are multiplied by their (and their surrounding elements) mechanical resonance. In a computer, these are the inductances of the power system, the current through which is modulated by the current supplying the processor. It also increases if the ferrite core of such a coil has the effect of magnetostriction.
But the main source of acoustic radiation in computers (processors) are SMD ceramic capacitors, which are located on a set of the processor and the motherboard and are included in the processor power supply circuit. They are intended to filter the supply voltage from the wideband interference generated by the processor in the power bus.
To obtain their high capacitance (0.1-100 microfarads), these capacitors are made of multi-layer capacitors and, of the dielectrics of classes II and III, have a significantly higher dielectric constant and, therefore, capacitance. They are piezoelectric, therefore, a mechanical effect on them produces voltage, that is, they are subject to a microphone effect. And vice versa, when an alternating voltage is applied to them, they tend to convert it into vibrations and, accordingly, an acoustic wave. And the more layers (the greater the capacity) of such a capacitor, the greater the amplitude of the acoustic wave. These effects do not affect the operation of most power sources, unless the operating frequency is in the audio range.
The voltage filtered by them is applied to the plates of multilayer ceramic SMD capacitors, where the variable component of the voltage creates an acoustic wave.
So what to do?
You can reduce the power of a computer-generated acoustic field and, accordingly, the probability of extracting encryption keys:
- Programmatically using special algorithms that provide variable intervals between key use cycles. This will create a blur of the analyzed acoustic wave and reduce its level.
- Properly calculating the filtering system of the processor supply voltage throughout the circuit from the source (multiphase inverter) along the distribution lines of the processor and further on the processor itself - the lower the level of the acoustic wave generated by the computer (the same applies to electromagnetic radiation).
- With the help of competent design of the computer case and the use of sound-absorbing materials, this will not cause any particular difficulties, because the frequency range of the acoustic wave is quite high (although this will not solve the problem of electromagnetic radiation and will allow you to read the information using external devices connected at least to the USB port).
But this is more true of computer hardware manufacturers and programmers, but for now we only have to put the computer on the vibration-absorbing surfaces, look around more often and not connect incomprehensible gadgets to the computer.
Source: https://habr.com/ru/post/206974/
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