Safety-critical systems are embedded systems whose failure or malfunction could lead to unacceptable consequences. Despite the major worries about such systems are related to the design of its embedded software, the security is still a challenge to be faced, particularly in terms of data confidentiality, since they could store sensitive that, such as cryptographic keys, which could not be revealed by unauthorized people. Assuming that safety-critical systems are commonly arranged in unprotected areas, without being under surveillance, an attacker could easily capture the respective devices in order to disclosure its cryptographic keys. Thus, it is necessary to create solutions to keep cryptographic keys secret. In this paper is proposed methods to protect cryptographic keys based on code transformations. Since all major protections stand up to a determined attacker’s strategies till a certain period of time, we propose methods taking into account what strategies the attacker can perform. We conducted a case study and a discussion to show the difficulty to disclosure cryptographic keys if were used one or more methods proposed here.