4.1.1.3 First Mutable Code in Flash

Security Objectives:

• Integrity
• Authenticity
• Availability

The first mutable code is the first code in the system that could be updated through a firmware update. Secure boot and secure firmware update are use cases that are often used together. The first mutable code could be the end application code, a second stage boot loader/firmware update system or an operating system in more complex systems. Each layer in the system is responsible for booting the next layer in the mutable layer/code starting from the root of trust to form a chain of trust through each software loaded.