Ascon algorithm was selected in 2019, in the CAESAR competition as the first option for lightweight applications as an alternative to AES-GCM for authenticated encryption. As with other encryption algorithms, Ascon relies on some parameters and security assumptions to guarantee its security. For example, if the number of rounds of the initialization phase of the encryption is reduced, the key can be obtained using a cube attack. In this work we describe how by inserting a hardware trojan with low overhead in a hardware implementation of Ascon, it is possible to reduce the number of rounds of its initialization stage and perform a cube attack in order to obtain the key in 94 seconds on average.