Israeli security researches at Tel Aviv University have published a paper called “RSA Key Extraction via Low-Bandwidth Acoustic Cryptanalysis”. They claim that they can extract keys used in 4096-RSA, one of the most secure encryption algorithms, by capturing the sound generated by CPU during decryption. The microphone can be a mobile phone placed very close to the PC or a sensitive microphone placed 4 meters away. One of the researchers is Adi Shamir who is the S in RSA and he co-invented the RSA encryption algorithm.
In order for the key extraction to be successful the encrypted text needs to follow a certain mathematical patterns. Then they listen at a high-pitched (10-150 KHz) sound of the CPU while it decrypts the data and by using acoustic cryptanalysis the key can be extracted. It is amazing that you can get decryption keys of such high-secured encryption algorithm without a connection to the PC but with just hearing it. There are more to be discovered but for sure acoustic cryptanalysis gained more publicity with such discovery.