Update HMAC Key Register

This command is used to update the HMAC-Key register corresponding to the received Counter Address with a new HMAC key calculated based on received input.

This command is issued on every power cycle event. This HMAC key is stored in volatile memory.

RPMC Update HMAC Key Register OOB Command:

Response:

After the command is issued, the device ensures that the received transaction is error free. This includes checking following conditions:

• RPMC message payload size is correct (including OP1 = 40 bytes)
• Counter Address falls within the range of supported counters.
• The Monotonic Counter corresponding to the requested Counter Address was previously initialized.
• Signature matches the HMAC-SHA-256 based signature computed based on received input parameters. This command performs two HMAC-SHA-256 operations.
  • HMAC-SHA-256 Operation 1 Output = HMAC_​Storage[255:0]
    • HMAC Message[31:0] = KeyData[31:0]
    • HMAC Key[255:0] = Root_​Key_​Register[CounterAddr][255:0]
  • HMAC-SHA-256 Operation 2 Output = HMAC-SHA-256 based signature[255:0]
    • HMAC message[63:0] = (OpCode[7:0],CmdType[7:0].CounterAddr[7:0].Reserved[7:0], KeyData[31:0])
    • HMAC Key[255:0] = HMAC_​Storage[255:0]

If the received transaction is error free the device successfully executes the command and posts “successful completion” extended status.

If the received transaction has errors, the device does not execute the transaction and posts the corresponding error in extended status.

Expected Extended Status [7:0] results:

Flow Diagram for Command:

Figure 3-2. Update HMAC Key