Cr51 Image Signature Library

Package libcr51sign

• Status: Ready

Libcr51sign is a library to verify images signed in the Cr51 format which can be shared between all systems requiring this functionality. Given an absolute start and end offset the library would scan for and validate the signature on the image descriptor, if the image validates, hashes the rest of the image to verify its integrity. Because this library will be used across many varied platforms, it does not assume the presence of any standard libraries or operating system interfaces. In order to handle this, a struct containing function pointers that implement each piece of platform-specific functionality will be passed to the library’s functions. Interface struct should typically be static data (could put in rodata) while the data in context is mutable.

Debug

Print will be handled via Macros. The user can define USER_PRINT or the library would use its default. The library will not assert on any error conditions,but will return error codes and expects the client to handle as deemed fit.

#ifndef USER_PRINT
#define CPRINTS(ctx, format, args...)printf(format, ##args)
#endif

Prod/Dev transitions

Prod --> Prod: Allowed
Prod --> Dev: Only if allowlisted/prod_to_dev_downgrade_allowed
Dev --> Prod: Allowed
Dev --> Dev: Allowed

verify_signature: The implementation should check if the signature size passed is same as the length of the key

Note: libcr51sign will also provide a companion library with default SW implementations of common functions like hash_init/final, read_and_hash_update().