[simonh]

It started off as an implementation of TrustZone but has likely diverged significantly from it since. In any case 64bit ARM had architectural features to support the implementation if such technology. Doing so on 32 bit ARM would have been a huge amount of work, and really not feasible.

[astrange]

The Secure Enclave never used TrustZone. It's a physically separate processor. (Not that this matters.)