16.5.12 Security
The FTFE module provides security information to the MCU based on contents of the
FSEC security register. The MCU then limits access to FTFE resources as defined in the
device's Chip Configuration details. During reset, the FTFE module initializes the FSEC
register using data read from the security byte of the Flash Configuration Field (see
configuration field description
).
The following fields are available in the FSEC register. Details of the settings are
described in the FSEC register description.
Flash security features are discussed further in
AN4507: Using the Kinetis Security and
. Some features described in the application note may not be
available on this device.
Table 16-52. FSEC fields
FSEC field
Description
KEYEN
Backdoor Key Access
MEEN
Mass Erase Capability
FSLACC
Factory Security Level Access
SEC
MCU security
16.5.12.1 Changing the Security State
The security state out of reset can be permanently changed by programming the security
byte of the flash configuration field. This assumes that you are starting from a mode
where the necessary program flash erase and program commands are available and that
the region of the program flash containing the flash configuration field is unprotected. If
the flash security byte is successfully programmed, its new value takes effect after the
next MCU reset.
16.5.12.1.1 Unsecuring the MCU Using Backdoor Key Access
The MCU can be unsecured by using the backdoor key access feature which requires
knowledge of the contents of the 8-byte backdoor key value stored in the Flash
Configuration Field (see
Flash configuration field description
are in the enabled state, the Verify Backdoor Access Key command (see
) can be run which allows the user to present prospective keys for
comparison to the stored keys. If the keys match, the FSEC[SEC] bits are changed to
unsecure the MCU. The entire 8-byte key cannot be all 0s or all 1s, i.e.
0x0000_0000_0000_0000 and 0xFFFF_FFFF_FFFF_FFFF are not accepted by the
Functional Description
Kinetis KE1xZ256 Sub-Family Reference Manual, Rev. 3, 07/2018
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