This post is part of a series of 3 where we will give our solutions to the Kudelski CTF. In this post, we give our solution on the first challenge. Kudelski organized a Capture The Flag (CTF) during last summer. The prize was very attractive: A Ledger Nano S with 100 USD in Ethereum! Kudelski CTFs are very interesting, challenging and cryptography related. At Ledger, we have the Donjon team which evaluates the security of our products, hardening them and doing security research. Our areas of expertise include Side Channel Attacks, Fault Attacks and Software Attacks on various architectures. Even though we were quite busy this summer, we found time to try to attempt the CTF. They were quite difficult, thus we are very proud to have solved them. Furthermore, we were the first to do this and we won the CTF! We could sadly not attend DEFCON this summer, but for winning the CTF, Kudelski has sent us our precious device 🙂 Our prize for winning the CTF: A Ledger Nano S with 100 USD in Ethereum We would like to thank Kudelski for this very smooth organization of this great challenge. Kudelski asked us to prepare a write-up explaining how we solved the challenges. […] L’article Ledger Donjon Wins the Kudelski Crypto Challenge: Behind the scenes (1/3) - One Fault is Enough to Break EdDSA est apparu en premier sur Ledger.