Its not any different than any of the DSP or CSP tunes that EFILive claims as theirs yet it's 99.99% OEM Code. And no info is needed from GM. Just an understanding of how processors work. Just think LB7 & LLY locking. No real need to over complicate it.
I would argue that is not AT ALL the case - the older ECMs - LB7, LLY, LBZ, LMM and probably even LML, would generally accept whatever you tried to flash them (within reason), even if it had issues which caused it to brick - what has been done here is different. With previous generations, all tuning was done on a GM OS. With the DSP & CSP, yes, it was largely a GM (or Cummins) OS that was modified to accept multiple tunes based on specific inputs. But in the end, it was not corrupted and acceptable for the processor, so it ran. With the L5P, the same *could* apply, *except* for the signature verification part. I won't claim to know EXACTLY how it works - whether it's part of the CPU, the flash memory, or some combination, but the fact that they are replacing the CPU suggests that it's part of the CPU.
That being said, what Dave and Tony said makes total sense. They could have replaced the CPU with one that had no keys to the door - but that would have allowed other companies like EFILive to tune any ECM that they unlocked - In my opinion, I think that's a bit overboard, since at this point, they're charging a nice chunk to unlock, but whatever - point being, all they appear to have have done is changed the lock on the door (While I hadn't thought of this, I met Tony a number of years ago, and IMO, he is and was a straight shooter, so if he says that IS what they did, I personally have no reason to doubt him), not what is behind it any more than was the case for non-DSP or CSP OSes from EFILive - where all we did was read what was in the ECM, make changes and flash it back. In the end, I strongly suspect that the HPT L5P tuning is no different from HPT or EFI tuning of LB7, LLY, LBZ, LMM and even to a degree, LML tuning, (except for the DSP OSes), with the only exception being the signature verification (keys), which they have changed in their modded processors.
To break it down to the most basic level, it's no different than EFILive's ability to lock ECMs by changing it's seed/key pair which prevents reads and writes (except for the newer ECMs like the LBZ, LMM and maybe LML that allow writes but not reads, however that works). Just a different mechanism is used.