## 5 Proposed Solution
### Integration of SE in the SCM  
To demonstrate the integration of the solution, a distributed-ledger infrastructure for supply chain management is properly deployed. The infrastructure used is taken from [49] and the details are out of the scope of this research. In this context, the focus is on a common SCM functionality that provides ownership tracking capabilities of a given part inside the supply chain. From a high-level point of view, the SCM stores the current owner and exposes services to record ownership changes to follow the part inside the manufacturing process from the suppliers to the final customer. As baseline, an SE is provided with strong private keys, the manufacturing certificates, and a certificate showing part validity (which can be used as oracle certificates [50]).  
The SCM is coordinated by a smart contract, which is validated by all the stakeholders and stored in a permissioned blockchain.  
Figure 1 presents a functionality scheme of the interactions between the stakeholders, the SE, and our blockchain SCM system. Notice that the yellow diamonds shall be successful before passing to the next steps, delivering robust tracking capabilities and consistent information. Firstly, the supplier receives and accepts an order for a specific part. Then, the part manufacturing and shipping starts:  
1. A supplier physically packages the part to be shipped and prepares it to be traced in the SCM by performing the following: * The SE is enrolled to the blockchain, registering its identity, the SE's manufacturer certificates, and the physical part that it is linked to. * The smart contract verifies the certificates to assert the SE trustworthiness. * After verifying the certificates, the SCM approves the use of this SE as a part tag, stores its public key, and attaches it to the order. * The SE is finally attached physically to the part, and the tampering security controls are deployed. 2. The supplier physically and digitally delivers the part to the next actor in the supply chain, the distributor. The digital change in ownership requires the use of two random numbers (\"Challenge\" and \"Challenge-proposed\"), as explained in detail in Section 5.2, to avoid prediction attacks and delay attacks defined in Section 7.2. * The distributor uses the SE attached to the received part to sign a transaction for the blockchain.  
Figure 1: Overview of the proposed interactions.  
The blockchain verifies that the SE used to sign the transaction is authentic and, consequently, the delivery part. * The distributor uses their own credentials to send a transaction to the blockchain accepting the part. * Finally, the smart contract accepts and records the new part owner. * The change in ownership is repeated successively between the supply chain partners until the smart part reaches the final customer.  
The scheme shows that only when the distributed ledger verifies the part can it be accepted, and the change in ownership can be recorded permanently in the blockchain. With this system, all the important steps of the product life cycle are verified by consensus and then recorded. This guarantees a correct verification and of the recorded data and that it has not been tampered with. Thus, this approach enables any stakeholder, like the final customer or any other authorized third party, with read access to the smart contract to accurately monitor in real-time the status and the history of a part in the supply chain.