hello julien.moinard,
had you refer to Security chapter, which describes the details of security features?
SecureBoot establishes the root of trust and maintains the chain of trust by authenticating each stage, boot component is signed using private key.
you may also check Jetson Xavier NX and Jetson AGX Xavier Series Boot Flow for reference,
BTW,
here’re also some similar forum discussion threads you should also check about Jetson security, thanks