Defeating any secret cryptography with SCARE attacks

This article aims at showing that side-channel analyses constitute powerful tools for reverse-engineering applications. We present two new attacks that only require known plaintext or ciphertext. The first one targets a stream cipher and points out how an attacker can recover unknown linear parts of an algorithm which is in our case the parameters of a Linear Feedback Shift Register. The second technique allows to retrieve an unknown non-linear function such as a substitution box. It can be applied on every kind of symmetric algorithm (typically Feistel or Substitution Permutation Network) and also on stream ciphers. Twelve years after the first publication about side-channel attacks, we show that the potential of these analyses has been initially seriously under-estimated. Every cryptography, either public or secret, is indeed at risk when implemented in a device accessible by an attacker. This illustrates how vulnerable cryptography is without a trusted tamper-proof hardware support.