Adapting SBSFU AN5056
34/49 AN5056 Rev 8
7 Adapting SBSFU
7.1 Implementing a new cryptographic scheme for SBSFU
X-CUBE-SBSFU comes with some predefined cryptographic schemes (Refer to
Section 4.2: Cryptographic scheme selection on page 21). It is also possible to extend the
package with the user’s cryptographic scheme.
To implement a new cryptographic scheme for SBSFU, follow the steps illustrated in
Figure 31 and described below.
Figure 31. User’s cryptographic scheme implementation
Updating the code running on the device side:
1. Step 1: define a new value for SECBOOT_CRYPTO_SCHEME.
2. Step 2: look carefully at the signatures of the APIs that the bootloader requires. The
cryptographic services must have the same signatures to avoid updating the SBSFU
code.
3. Step 3: define a new SE_FwRawHeaderTypeDef structure and respect the constraints
to remain compatible with the existing SBSFU code.
4. Step 4: implement the code of the cryptographic services in se_crypto_bootloader.c.
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