Physical attacks are a known threat posed against secure embedded systems. Notable among these is laser fault injection, which is often considered as the most effective fault injection technique. Indeed, laser fault injection provides a high spatial accuracy, which enables an attacker to induce bit-level faults. However, experience gained from attacking 8-bit targets might not be relevant on more advanced micro-architectures, and these attacks become increasingly challenging on 32-bit microcontrollers. In this article, we show that the flash memory area of a 32-bit microcontroller is sensitive to laser fault injection. These faults occur during the instruction fetch process, hence the stored value remains unaltered. After a thorough characterisation of the induced faults and the associated fault model, we provide detailed examples of bitlevel corruption of instructions and demonstrate practical applications in compromising the security of real-life codes. Based on these experimental results, we formulate a hypothesis about the underlying micro-architectural features that explain the observed fault model.

Code-based public-key cryptosystems are promising candidates for standardization as quantum-resistant public-key cryptographic algorithms. Their security is based on the hardness of the syndrome decoding problem. Computing the syndrome in a finite field, usually F2, guarantees the security of the constructions. We show in this article that the problem becomes considerably easier to solve if the syndrome is computed in N instead. By means of laser fault injection, we illustrate how to compute the matrix-vector product in N by corrupting specific instructions, and validate it experimentally. To solve the syndrome decoding problem in N, we propose a reduction to an integer linear programming problem. We leverage the computational efficiency of linear programming solvers to obtain real-time message recovery attacks against the code-based proposal to the NIST Post-Quantum Cryptography standardization challenge. We perform our attacks in the worst-case scenario, i.e. considering random binary codes, and retrieve the initial message within minutes on a desktop computer. Our attack targets the reference implementation of the Niederreiter cryptosystem in the NIST PQC competition finalist Classic McEliece and is practically feasible for all proposed parameters sets of this submission. For example, for the 256-bit security parameters sets, we successfully recover the message in a couple of seconds on a desktop computer. Finally, we highlight the fact that the attack is still possible if only a fraction of the syndrome entries are faulty. This makes the attack feasible even though the fault injection does not have perfect repeatability and reduces the computational complexity of the attack, making it even more practical overall.