Analog Devices ADSP-SC58 Series Hardware Reference Manual page 3470

Secure Boot
Secure boot increases protection against malicious, unsecured accesses to critical and confidential resources of the
processor. The boot stream application code and data must be digitally signed in order to build up a chain of trust in
the system. This allows the processor to distinguish between authentic and trusted code from non-authentic and
untrusted code.
Secure boot also provides confidentiality support. The digitally signed boot image can be optionally encrypted as
well. When loading an encrypted image, the ROM decrypts while loading, then authenticates, before any applica-
tion code is executed.
Secure boot is an optional feature of the processor and is disabled by default. The feature is enabled using the OTP
lock API, and secure boot cannot be disabled after it has been enabled. When security is enabled, developers are not
dependent upon on Analog Devices to provision the devices, sign code or provide security certificates. The required
tools for signing and encrypting the boot images are provided with the development tools for the processor.
Integrity and Authenticity Protection
Integrity protection is based on the secure hash SHA-2 224 bit algorithm. Authenticity protection is based on the
ECDSA algorithm.
ECDSA uses public key cryptography consisting of two keys, a private key and a public key. The public key is stored
in OTP memory on the processor so that the secure boot process can verify the authenticity of the signed boot im-
age. Only parties in possession of the private key are able to sign the images.
Confidentiality Protection
Confidentiality protection uses the AES algorithm. Two variants are supported, wrapped and unwrapped.
The wrapped variant utilizes a 128-bit Key Encryption Key (KEK) stored on the processor to decrypt the 128-bit
AES decryption key embedded in the secure header. The unwrapped variant stores the AES description key on the
processor and utilizes it to decrypt the entire image.
The privacy of the key stored on the device (whether AES or KEK) is paramount to the security of the system. Dis-
closure of this key compromises security of the entire system.
Anti-Cloning Protection
Anti-cloning protection is based on the confidentiality protection. If each processor uses a unique private key for the
confidentiality protection, then cloning between these devices can be prevented. The boot image is incompatible
with devices using a different private key for the decryption.
Anti-Rollback Protection
The secure boot process supports anti-rollback protection through a 32-bit counter in the OTP memory. A value of
0x00000000 in the OTP results in anti-rollback being disabled by default. If anti-rollback protection is required,
then the user may set the Rollback ID when signing the boot image. Upon successful authentication of the boot
image, the secure boot software then updates the counter in the OTP. The software updates the counter if the roll-
back ID in the boot image is greater than the value currently stored in the OTP counter.
53–50 ADSP-SC58x/ADSP-2158x SHARC+ Processor Hardware Reference