tree ec2d532ef424db77362d3bd2fa95c6996620016c
parent e65e0597a83fbf74dcd8d91a639b3a77586a82d5
author Janos Follath <janos.follath@arm.com> 1546873292 +0000
committer Darryl Green <darryl.green@arm.com> 1567678738 +0100

Add warning for alternative ECDSA implementations

Alternative implementations are often hardware accelerators and might
not need an RNG for blinding. But if they do, then we make them misuse
the RNG in the deterministic case.

There are several way around this:
- Exposing a lower level function for replacement. This would be the
optimal solution, but litters the API and is not backward compatible.
- Introducing a new compile time option for replacing the deterministic
function. This would mostly cover the same code as
MBEDTLS_ECDSA_DETERMINISTIC and would be yet another compile time flag.
- Reusing the existing MBEDTLS_ECDSA_DETERMINISTIC macro. This changes
the algorithm used by the PK layer from deterministic to randomised if
the alternative implementation is present.

This commit implements the third option. This is a temporary solution
and should be fixed at the next device driver API change.