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December 20, 2013 AT 5:38 am

Crack RSA Encryption by Listening to Sound

Read about this scary side channel attack on RSA encryption, the paper is written partly by Adi Shamir, who is the co-inventor of the RSA algorithm. It describes how RSA encryption can be broken by listening and analyzing the sounds that a CPU can make, using equipment as simple as a cellphone.

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Many computers emit a high-pitched noise during operation, due to vibration in some of their electronic components. These acoustic emanations are more than a nuisance: they can convey information about the software running on the computer and, in particular, leak sensitive information about security-related computations. In a preliminary presentation, we have shown that different RSA keys induce different sound patterns, but it was not clear how to extract individual key bits. The main problem was the very low bandwidth of the acoustic side channel (under 20 kHz using common microphones, and a few hundred kHz using ultrasound microphones), many orders of magnitude below the GHz-scale clock rates of the attacked computers.

Here, we describe a new acoustic cryptanalysis key extraction attack, applicable to GnuPG‘s current implementation of RSA. The attack can extract full 4096-bit RSA decryption keys from laptop computers (of various models), within an hour, using the sound generated by the computer during the decryption of some chosen ciphertexts. We experimentally demonstrate that such attacks can be carried out, using either a plain mobile phone placed next to the computer, or a more sensitive microphone placed 4 meters away.

What is making the noise?

The acoustic signal of interest is generated by vibration of electronic components (capacitors and coils) in the voltage regulation circuit, as it struggles to supply constant voltage to the CPU despite the large fluctuations in power consumption caused by different patterns of CPU operations.

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1 Comment

  1. Makes me wonder what you could do with RF instead of audio…

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