This work presents two implementation attacks against cryptographic algorithms. Based on these two presented attacks, this thesis shows that the assessment of physical attack complexity is error-prone. Hence, cryptography should not rely on it. Cryptographic technologies have to be protected against all implementation attacks, have they already been realized or not. The development of countermeasures does not require the successful execution of an attack but can already be carried out as soon as the principle of a side channel or a fault attack is understood.