## 3 Blockchain and Tracking Technologies in the Raw Material Sector
### Blockchain Architectures  
An essential element that can provide for the integrity of a blockchain architecture is that it is built on the distributed ledger technology (DLT) [18]. DLT means that an ordered list of transactions is replicated over multiple nodes [19]. Nodes are the instances that not only keep replicas of the data on the blockchain but also need to agree on an execution order of transactions [19]. As another essential element to provide for the integrity of the ledger and as illustrated in Figure 1, a blockchain establishes a consecutive chain of encrypted and hashed blocks of data, whereas every block is timestamped and immutably linked to the previous block by including a hash of the previous block [18]. In doing so, the blockchain technology takes advantage of an important distinction between encryption and hashing. Encryption is bi-directional: Data can be encrypted and decrypted. It always can be reverted back. Hashing is one-directional only: When a hash code is generated from data, this hash result is always the same. In case the respective data is modified, the generated hash code will be different. The same applies if encrypted data is hashed. The hash code generated from the encrypted data is always the same. Therefore, by comparing hash codes one can identify if the data matches or not (even if the data was encrypted). Because the users or owners of the nodes in a blockchain environment may not trust each other, its decentralized setup and an appropriate consensus mechanism ensures that the processing and replication of data is managed without depending on a trusted individual person or instance. And there is a growing variety of blockchain architectures that are usually designed in consideration and combination of the following principles and their variations [2; 10; 19; 20]:  
* The consensus protocol: for example, authorization and procedures to register and seal blocks are based on proof-of-work (PoW), proof-of-authority (PoA), proof-of-stake (PoS), proof-of-elapsed-time (PoET), or other variations or types of protocols [21]. These differing consensus protocols also determine the amount of energy a blockchain will consume in order to validate transactions. * Node control: the governing structure to run nodes in a blockchain. For example, anyone can join to run a node in a public blockchain without further authentication, whereas in a private blockchain, every node is authenticated and its identity is known to the other nodes. * Access control: for example, anyone may initiate or read transactions in a permissionless blockchain, whereas limitations may apply in a permissioned blockchain. * Smart contract execution: depending on the specifications and rules of the blockchain environment to initiate automated execution procedures referred to as \"smart contracts\", users may be allowed to customize transaction logics to suit their applications. In the context of supply chain transparency and traceability along complex supply chains, the main benefits of the blockchain technology can be its high level of immutability and transparency, because it can create unique digital documents, whose manipulation can be immediately detected by independent participants, since the information is stored on different blocks that are time-stamped and interlinked in a way that one block can't be modified without effect on the other blocks in the chain. These characteristic features of blockchain technology appear particularly suitable for creating transparency within complex supply chains, where collaboration across multiple supply levels is challenging due to a lack of knowledge or trust between suppliers. However, key limitations compared to other database architectures are:  
* Level of complexity [19]: Depending on the design of the consensus mechanism and other components of the blockchain environment, this can generate greater complexity compared to usual database architectures.