A Security Scheme for Dependable Key Insertion in Mobile Embedded Devices

Algorithm 5

Indirect flashing protocol over a trusted mediator (no online connection to OEM).

Requirements

  (i) The initialization protocol has been completed successfully.

  (ii) UD has knowledge of VK_OEM.

   (iii) SP has a valid trust key pair and has not reached the maximum quota 𝑁 of

    allowed flashing procedures.

Protocol

Step  1: SP contacts UD and sends 𝚂𝚒𝚐_{SK𝙾𝙴𝙼}(VK_𝚂𝙿,VK^TD_𝚂𝙿,𝑇,𝑁) to UD.

Step  2: UD verifies 𝑉(𝚂𝚒𝚐_{SK𝙾𝙴𝙼}(VK_𝚂𝙿,VK^TD_𝚂𝙿,𝑇,𝑁),VK_𝙾𝙴𝙼)=^!1

   and sends back 𝚂𝚒𝚐_SK𝚄𝙳(VK_𝚄𝙳,VK_𝚂𝙿) as an acknowledge.

Step  3: OWN authorizes the start of a key flashing procedure by presenting

   a valid TRK_orig. UD authenticates TRK_orig using the internally

   stored VK_{𝚃𝚁𝙺orig} and a PKC authentication protocol.

Step  4: SP sends the certified new key package 𝚂𝚒𝚐_SK^TD_𝚂𝙿(𝚂𝚒𝚐_{SK𝙾𝙴𝙼}(VK_{𝚃𝚁𝙺new},VK_𝚂𝙿),VK_𝚄𝙳) to UD.

Step  5: UD verifies that 𝑉(𝚂𝚒𝚐_SK^TD_𝚂𝙿(S_{SK𝙾𝙴𝙼}(VK_{𝚃𝚁𝙺new},VK_𝚂𝙿),VK_𝚄𝙳),VK^TD_𝚂𝙿)=^!1 and

   𝑉(𝚂𝚒𝚐_{SK𝙾𝙴𝙼}(VK_{𝚃𝚁𝙺new},VK_𝚂𝙿),VK_𝚄𝙳,VK_𝙾𝙴𝙼)=^!1. Then the new transponder TRK_new can be

    activated: TRK_new↦TRK_orig. The protocol is completed by sending a DONE-message to SP.