Side-channel attacks can recover secret keys from cryptographic algorithms (including the pervasive AES) using measurements such as power use. However, these previously-known attacks on AES tend to require unrestricted, physical access to the device.

Using improved antenna and signal processing, Fox-IT and Riscure show how to covertly recover the encryption key from two realistic AES-256 implementations while: Attacking at a distance of up to 1 m ( 30 cm in realistic conditions; „TEMPEST“), 1. Using minimal equipment (fits in a jacket pocket, costs less than €200) and 2. Needing only a few minutes (5 minutes for 1 m and 50 seconds for 30 cm ).

3. To the best of our knowledge, this is the first public demonstration of such covert attacks from a distance.