Since the need for post-quantum cryptography emerged the interest in hash-based signatures (HBS) has significantly increased. Since their standardization especially stateful HBS like XMSS have been deployed in several products ranging from embedded devices up to servers. The Fraunhofer institute AISEC has authored a study on behalf of the BSI, which describes the practical evaluation of a new kind of Laser Fault Injection Attack on the Winternitz One-Time Signature (WOTS) scheme, which is also used in XMSS. The study describes the preparation and implementation of the attack on a standard microcontroller as well as the difficulties the attacker has to overcome. Additionally it presents a countermeasure, which is easy to implement and can increase the effort for an attacker significantly.

In practice, stateful HBS are most applicable to verify the integrity and authenticity of data that rarely changes, such as the firmware of embedded devices.

Due to their mobility embedded systems are not only exposed to attacks with quantum computers. Here also special attacks come into play that are not targeting weak spots in the software, but use properties of the hardware itself. These hardware attacks include Side Channel and Fault Injection Attacks.

In this study a Laser Fault Injection Attack on the WOTS scheme is practically evaluated. The attack can be mounted on different HBS schemes, such as LMS, XMSS and SPHINCS+.

Laser Fault Injection Attack on the eXtended Merkle Signature Scheme (XMSS)