## 3 The Critical Importance of Product Identity in Agricultural Supply Chains
### Implementation Considerations for DIDs and Digital Twins  
The deployment of Decentralised Identifiers (DIDs) and digital twins in agricultural supply chains requires a thorough understanding of their technical foundations, standardisation efforts, and operational viability. This section offers a detailed analysis of how DIDs are created, resolved, and linked to physical assets through digital twins, addressing critical concerns from stakeholders. DIDs are generated following specific DID methods, such as did:ion, did:ethr, or did:key, which dictate the processes for identifier creation, registration, and resolution. In the presented framework, every supply chain entity, including farms, distributors, and product batches, receives a DID issued by a decentralised ledger system aligned with W3C standards. The issuance process may be managed by trusted authorities or automated via smart contracts triggered by verifiable production or certification events. The DID document holds important metadata, including public keys for authentication and encryption, service endpoints for interacting with digital twins or metadata APIs, and proof of control mechanisms. Resolving a DID involves querying a DID resolver that retrieves the associated DID document from the distributed ledger using protocols such as REST APIs or universal resolvers, enabling real-time verification of identity, and authorisation and credential validity across the supply chain. Digital twins in this model serve as virtual representations of physical products, such as grape batches or coffee sacks, augmented with IoT data such as temperature, humidity, and location. These digital twins are continuously updated with the physical state through sensor data streams, including RFID, GPS, and thermal probes, as well as manual verification logs such as quality control scans and video uploads. To securely associate physical and digital identities, cryptographic tags such as QR codes, NFC, or RFID embed unique nonces that are hashed and stored on-chain. Tag verification algorithms confirm that scanned tags correspond to the digital twin's DID, while anomaly detection methods, including geofencing checks and detection of duplicate tag reads, identify tampering attempts such as spoofing or tag switching. In Figure 4, the DID lifecycle--creation, resolution, and verification--is shown in conjunction with verifiable credentials and digital twins, highlighting how these components interoperate to ensure secure, standards-based identity and traceability.  
These mechanisms enable robust authentication and traceability of agricultural goods from origin to point-of-sale.  
This implementation follows the W3C DID core specification and incorporates several key components. verifiable credentials (VCs) are used as tamper-evident claims, such as organic certification, issued by recognised authorities and cryptographically linked to the  
Figure 4: Diagram illustrating emerging role of DIDs in agri-food supply chains.  
DID. The universal resolver (UR) is employed as a protocol-agnostic tool compatible with multiple DID methods, enabling flexible resolution. Additionally, DIDComm is utilised as a protocol for secure peer-to-peer messaging between supply chain participants, relying on DID-based authentication. Among the example frameworks and tools, DIDChain [55] illustrates supply chain DID workflows, including role-based access, credential issuance, and verification. Hyperledger Indy and Aries offer open-source tools that support the construction of interoperable DID and VC ecosystems, facilitating peer DIDs, credential exchanges, and integration with distributed ledgers.  
Figure 5 illustrates the sequential steps: DID issuance via standardised methods (e.g., Hyperledger Indy/Aries), product tagging and physical-digital linkage, creation of the digital twin, and synchronisation through a permissioned blockchain using verifiable credentials and DID resolution protocols.