3.2.4 ECC608-TFLXWPC Detailed Slot Access Policies

The ECC608-TFLXWPC default configuration for WPC uses only the information associated with WPC Slot 0. All information in the device slots associated with WPC Slot 0 is mandatory as part of the authentication procedure or certificate chain, with the exception of the WPC Slot 0 digest stored in Slot 3.
Attention: Check with Microchip prior to using features beyond the default WPC Slot 0 configuration as not all features are initially implemented in the provisioning systems.
The ECC608-TFLXWPC provides flexibility in two areas.
  1. Whether slots are permanently locked or slot lockable.
  2. Whether secure boot is connected to keys and the persistent latch.

Slot Locking Options

Slot locking options are called out for each individual slot and will be one of two types:

Slot Lockable
A slot that has the slot lock option set allows the end user to lock the slot at some point in the future after the initial manufacturing phase. This can be used to allow for a key to be set during a subsequent manufacturing step outside of Microchip or by the end user. The slot can be locked using the Lock command. Once the slot is locked, no future modifications to the data in the slot is possible.
Permanent Lock
A permanently locked slot can never be updated once it leaves the Microchip manufacturing facilities. The correct data or key must be provided to Microchip prior to the provisioning of these devices.

Secure Boot Option

The secure boot access policies provide an option to limit what commands are run prior to a successful secure boot or to provide unlimited command access. The ECC private keys in Slot 0, 1 and 2 may be set to require a secure boot before these keys are authorized for use for most commands. To use this feature, a change to the secure boot configuration settings and to the key configuration values is required. These configuration changes will set the persistent latch upon a successful secure boot. The slot access policy changes for Slot 0 tie use of the key to the persistent latch being set.

Persistent Latch Operation

The persistent latch will retain its state even during Idle and Sleep modes. This allows for a single secure boot operation to be run only once after initial power-up. If the device supply voltage goes below the minimum allowed value, the persistent latch will be reset and a new secure boot operation will need to be performed.

Prototype Units

Prototype units come with a specific default configuration that cannot be changed. The default configuration has all the Slots’ options set to Slot Lockable. This provides maximum flexibility when developing software to reprogram keys by an application. The final configuration does not need to be set this way. The secure boot option is not available with the prototype units. This option can only be selected for production units. Prototype units are only available with an I2C interface.

Detailed Slot Configurations

The following tables provide a more detailed description of the slot configuration and key configuration settings for each configured slot on the device. Relevant commands and command modes applicable to each configured slot are included. The table provides all allowed key and slot configuration values available for the ECC608-TFLXWPC device on a slot by slot basis.

Table 3-6. Slot 0 Configuration Information
Slot Configuration Value Description of Enabled Features
0 Option 1: Not Connected to Persistent Latch
Key: WPC Slot 0 ECC Private Key
  • Contains P-256 NIST ECC private key
  • The corresponding public key can always be generated
  • Random nonce is required
Slot:
  • Slot is secret
  • Can sign external messages
Option 2: Connected to Persistent Latch
Key: Same as above plus:
  • Secure boot must be run before this key can be used
Slot: Same as above
Table 3-7. Slot 1 Configuration Information
Slot Configuration Value Description of Enabled Features
1 Option 1: Not Connected to Persistent Latch
Key: WPC Slot 1 ECC Private Key
  • Contains P-256 NIST ECC private key
  • The corresponding public key can always be generated
  • Random nonce is required
Slot:
  • Slot is secret
  • Can sign external messages
Option 2: Connected to Persistent Latch
Key: Same as above plus:
  • Secure boot must be run before this key can be used
Slot: Same as above
Table 3-8. Slot 2 Configuration Information
Slot Configuration Value Description of Enabled Features
2 Option 1: Not Connected to Persistent Latch
Key: TLS Session Private Key
  • Contains P-256 NIST ECC private key
  • The corresponding public key can always be generated
  • Random nonce is required
Slot:
  • Slot is secret
  • Can sign external messages
  • Can use with ECDH command
Option 2: Connected to Persistent Latch
Key:
  • Same as Option 1
  • Persistent Disable Option Enabled
Slot:
  • Same as Option 1
Table 3-9. Slot 3 Configuration Information
Slot Configuration Value Description of Enabled Features
3 Option 1: Permanently Locked
Key: WPC Slot 0 Digest
  • Contains 32-byte digest of WPC Slot 0 certificate chain
  • This slot is permanently locked
Slot:
  • Can always be read in the clear
  • Permanent
Option 2: Slot Lockable and Writable
Key:
  • Slot is lockable
Slot:
  • Slot can be written in the clear
  • Slot can always be read
Table 3-10. Slot 4 Configuration Information
Slot Configuration Value Description of Enabled Features
4 Option 1: Permanent Data
Key: WPC Slot Other Data
  • Used to store WPC Slot 0 other data
  • Slot is permanent
Slot:
  • Can always be read in the clear
  • Permanent
Option 2: Slot Lockable and Writable
Key:
  • Used to store WPC Slot 0 other data
  • Slot is writable
Slot:
  • Can always be read in the clear
  • Slot can be locked
Table 3-11. Slot 5 Configuration Information
Slot Configuration Value Description of Enabled Features
5 Option 1: Permanent Data
Key: WPC Slot 0 Other Data (Cont)
  • Used to store WPC Slot 0 other data
  • Slot is permanent
Slot:
  • Can always be read in the clear
  • Permanent
Option 2: Slot Lockable and Writable
Key:
  • Used to store WPC Slot 0 other data
  • Slot is writable
Slot:
  • Can always be read in the clear
  • Slot can be locked
Table 3-12. Slot 6 Configuration Information
Slot Configuration Value Description of Enabled Features
6 Option 1: Slot is Lockable
Key: I/O Protection Key
  • Can contain a SHA-256 symmetric key or other data. If the I/O protection key is not used, this slot can be used for other data.
  • A random nonce is required when this key is used
  • This slot can be individually locked
Slot:
  • Data can be written in the clear
  • The contents of this slot are secret and cannot be read
  • Slot cannot be used for the CheckMac Copy command
Option 2: Permanent Lock
Key:
  • Same as Option 1 except the slot is permanently locked
Slot:
  • Same as Option 1 except the slot cannot be written
Important: In general, the I/O protection key stored in Slot 6 must be left to be slot lockable. In most cases, the I/O protection key is often unique to each device. If for some use case the I/O protection key is the same for all devices, a Permanent Lock option can be selected.
Table 3-13. Slot 7 Configuration Information
Slot Configuration Value Description of Enabled Features
7 Key: Secure Boot Digest
  • This slot is designated to be used for other data
Slot:
  • This slot cannot be directly written or read
  • This slot is secret and cannot be used by the MAC command
  • This slot cannot be used for CheckMac Copy command
Table 3-14. Slot 8 Configuration Information
Slot Configuration Value Description of Enabled Features
8 Option 1: Slot Lockable
Key: WPC Slot 1 Data
  • This slot is designated for WPC Slot 1 data
  • Slot is lockable
Slot:
  • Clear text writes and reads are permitted to this slot
  • Slot cannot be used for the CheckMac Copy command
Option 2: Permanent Lock
Key:
  • Same as Option 1 except the slot is permanently locked
Slot:
  • Same as Option 1 except the slot cannot be written
Table 3-15. Slot 9 Configuration Information
Slot Configuration Value Description of Enabled Features
9 Option 1: Permanently Locked
Key: WPC Slot 0 Public Key
  • Slot is defined for ECC key
  • ECC key is a public key
Slot:
  • Data cannot be overwritten
  • Data can be read in the clear

Option 2: Slot Lockable
Note: This Configuration is Used for Prototype Units
Key:
  • All features as shown in Option 1
  • Slot is lockable
Slot:
  • Same as Option 1 except the slot can be written
Table 3-16. Slot 10 Configuration Information
Slot Configuration Value Description of Enabled Features
10 Option 1: Permanently Locked
Key: Device Compressed Certificate
  • Slot defined to store other data
Slot:
  • Data cannot be overwritten
  • Data can be read in the clear

Option 2: Slot Lockable
Note: This Configuration is Used for Prototype Units
Key:
  • All features as shown in Option 1
  • Slot is lockable
Slot:
  • Same as Option 1 except the slot can be written
Table 3-17. Slot 11 Configuration Information
Slot Configuration Value Description of Enabled Features
11 Option 1: Permanently Locked
Key: Signer Public Key
  • Slot is defined for ECC key
  • ECC key is a public key
Slot:
  • Data cannot be overwritten
  • Data can be read in the clear

Option 2: Slot Lockable
Note: This Configuration is Used for Prototype Units
Key:
  • All features as shown in Option 1
  • Slot is lockable
Slot:
  • Same as Option 1 except the slot can be written
Table 3-18. Slot 12 Configuration Information
Slot Configuration Value Description of Enabled Features
12 Option 1: Permanently Locked
Key: Signer Compressed Certificate
  • Slot defined to store other data
Slot:
  • Data cannot be overwritten
  • Data can be read in the clear

Option 2: Slot Lockable
Note: This Configuration is Used for Prototype Units
Key:
  • All features as shown in Option 1
  • Slot is lockable
Slot:
  • Same as Option 1 except the slot can be written
Table 3-19. Slot 13 Configuration Information
Slot Configuration Value Description of Enabled Features
13 Option 1: Permanently Locked
Key: WPC Slot 0 Device Compressed Certificate
  • Slot defined to store other data
Slot:
  • Data cannot be overwritten
  • Data can be read in the clear

Option 2: Slot Lockable
Note: This Configuration is Used for Prototype Units
Key:
  • All features as shown in Option 1
  • Slot is lockable
Slot:
  • Same as Option 1 except the slot can be written
Table 3-20. Slot 14 Configuration Information
Slot Configuration Value Description of Enabled Features
14 Option 1: Permanently Locked
Key: WPC Slot 0 MFG Compressed Certificate
  • Slot defined to store other data
Slot:
  • Data cannot be overwritten
  • Data can be read in the clear

Option 2: Slot Lockable
Note: This Configuration is Used for Prototype Units
Key:
  • All features as shown in Option 1
  • Slot is lockable
Slot:
  • Same as Option 1 except the slot can be written
Table 3-21. Slot 15 Configuration Information
Slot Configuration Value Description of Enabled Features
15 Option 1: Slot is Lockable
Key: Secure Boot Public Key
  • Slot is defined for ECC key
  • Slot is lockable
Slot:
  • Always writable unless locked
  • Slot can always be read
Option 2: Permanently Locked
Key:
  • Same as Option 1 except the slot is permanently locked
Slot:
  • Same as Option 1 except the slot cannot be written