My bet:
1. Key inserted and turned to RUN
2. SKREEM reads chip in FOB
3. SKREEM compares secret code received to codes (8) stored in SKREEM
4. IF match, sends a unique start code to ECU (AKA PCM); IF NOT - failed start
5. ECU compares code received from SKREEM; IF match - engine starts

So, the Key FOB chip, SKREEM, and ECU all have VIN specific codes that are required to start.
As each VIN can have up to 8 keys, the SKREEM can accept 8 unique chip codes.

Hence, the FOB, SKREEM and ECU are required to successfully extract the unique start code from the SKREEM to be able to "spoof" the ECU with modified programming.

At least that's my guess...