ATECC508A datasheet(24/109 Pages) MICROCHIP

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All OTP bits have a value of one upon shipment from the Microchip factory.

2.4

EEPROM Locking

There are two separate lock states for the device:

•

One to lock the configuration zone (that is controlled by LockConfig, byte 87).

•

One to lock both the OTP and data zones (that are controlled by LockValue, byte 86).

These lock values are stored within separate bytes in the configuration zone, and they can be modified

only by means of the Lock command. After a memory zone is locked, there is no way to unlock it.

The device should be personalized at the system manufacturer’s site with the desired configuration

information; after which, the configuration zone should be locked. Then, all necessary writes of public and

secret information into the data and OTP zones should be performed by using encrypted writes, if

appropriate, and then the data and OTP zones should be locked.

It is vital that the data and OTP zones be locked prior to release into the field of the system containing the

device. Failure to lock these zones may permit modification of any secret keys and may lead to other

security problems.

Any attempt to read or write the data or OTP zones prior to locking the configuration zone causes the

device to return an error.

Note: Contact Microchip for optional secure personalization services.

2.4.1

Configuration Zone Locking

Certain bytes within the configuration zone can never be modified in the field regardless of the lock

status, per Table 2-5. Write permission for most of the remaining bytes within the zone is controlled using

the LockConfig byte in the configuration zone as shown in Table 2-13. Throughout this document, if

LockConfig is 0x55, the configuration zone is said to be unlocked; otherwise, it is locked. The LockConfig

byte can only be set via the Lock command. Once the configuration zone has been locked it can never

be unlocked and no values within the config zone can be updated via direct write commands. Some

configuration values can be set by other commands such as the Lock command when doing individual

slot locking. Values within the configuration zone can always be read.

Table 2-13. Configuration Zone Locking

Read Access

Write Access

LockConfig == 0x55 (unlocked)

Read

Write

LockConfig != 0x55 (locked)

Read

<Never>

2.4.2

Data and OTP Zone Locking

Once the configuration zone has been locked, secret and/or read-only data can be written into the slots of

the data zone and the OTP zone. Most write access restrictions are ignored when the data zone is

unlocked. Throughout this document, if LockValue is 0x55, then both the OTP and data zones are said to

be unlocked; otherwise, they are locked. The LockValue byte can only be set with the Lock command.

Locking the data/OTP zone does not mean that the values in these zones cannot be modified; locking

indicates that the slot now behaves according to the policies set by the associated configuration zone’s

values. Once the LockValue byte has been set it can never be cleared.

Note: There is neither read nor write access to the OTP and Data zones prior to locking of the

Configuration zone.

ATECC508A

Device Organization

Datasheet Complete

DS20005927A-page 24

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