There is an academic paper from Tel Aviv University examining Samsung smartphones and how they implement the cryptographic security. They found that some models had a design flaw that allowed for the extraction of the secret keys.
Trust Dies in Darkness: Shedding Light on Samsung’s TrustZone Keymaster Design (iacr.org)
Here is a more digestible version from The Register which lists the models tested:
Samsung shipped ‘100m’ Android phones with flawed encryption • The Register
