NXP Semiconductors MWCT101 S Series, Reference Manual, Page: 779 / 1761

Verify Backdoor Access Key command as valid comparison values. While the Verify
Backdoor Access Key command is active, program flash memory is not available for read
access and returns invalid data.
The user code stored in the program flash memory must have a method of receiving the
backdoor keys from an external stimulus. This external stimulus would typically be
through one of the on-chip serial ports.
If the KEYEN bits are in the enabled state, the MCU can be unsecured by the backdoor
key access sequence described below:
1. Follow the command sequence for the Verify Backdoor Access Key command as
explained in Verify Backdoor Access Key command
2. If the Verify Backdoor Access Key command is successful, the MCU is unsecured
and the FSEC[SEC] bits are forced to the unsecure state
An illegal key provided to the Verify Backdoor Access Key command prohibits future
use of the Verify Backdoor Access Key command. A reset of the MCU is the only
method to re-enable the Verify Backdoor Access Key command when a comparison fails.
After the backdoor keys have been correctly matched, the MCU is unsecured by changing
the FSEC[SEC] bits. A successful execution of the Verify Backdoor Access Key
command changes the security in the FSEC register only. It does not alter the security
byte or the keys stored in the Flash Configuration Field (
Flash configuration field
description ). After the next reset of the MCU, the security state of the FTFC module
reverts back to the Flash security byte in the Flash Configuration Field. The Verify
Backdoor Access Key command sequence has no effect on the program and erase
protections defined in the program flash protection registers.
If the backdoor keys successfully match, the unsecured MCU has full control of the
contents of the Flash Configuration Field. The MCU may erase the sector containing the
Flash Configuration Field and reprogram the flash security byte to the unsecure state and
change the backdoor keys to any desired value.
32.5.13 Cryptographic Services Engine (CSEc)
The FTFC module has added features to comply with the SHE
6
specification. It is
assumed that the user is familiar with the SHE specification, therefore we do not replicate
the document here.
6. HIS SHE Specification - Secure Hardware Extension Functional Specification; Version 1.0.1; Rev429 from 23.03.2009
Chapter 32 Flash Memory Module (FTFC)
MWCT101xS Series Reference Manual, Rev. 3, 07/2019
NXP Semiconductors 779