Three Israeli Security Researchers at Tel Aviv University recently published an interesting paper. They used a side channel attack and through a process called “acoustic cryptanalysis”, they successfully extracted 4096-bit RSA key from GnuPG. The researchers listen to the high-pitched (10 to 150 KHz) sounds produced by your computer as it decrypts data. An attacker can e-mail suitably-crafted messages to the victims, wait until they reach the target computer, and observe the acoustic signature of their decryption, thereby closing the adaptive attack loop.
Source: https://thehackernews.com/2013/12/acoustic-cryptanalysis-extracting-rsa.html