Page 15 - U4SSC Blockchain for smart sustainable cities

Furthermore, blockchain is increasingly being utilized in different smart city applications relating to
data access, control and sharing for the management of health records, energy and finance. Based
on the principles of its operation, various aspects related to blockchain including its taxonomies are
explored in this section. (For more details on the applications and use-cases examples, please refer to
section 4 of this report).

Concretely, blockchain can be described as a sequence of blocks, which holds a complete list of
transaction records like a conventional public ledger. These transactions or contracts are enclosed in
5
code and stored in transparent and shared databases where they are protected from deletion or change
without the need for the involvement of lawyers, banks or brokers or any other trusted third party.

In the blockchain's context, the data structure of records is organized as chained-blocks in such a way
that each new block includes information about the previous block using a cryptographic link in an
append-only pattern. Along with clear rules for participation and data appending, this structure is
designed to harden data records against tampering while providing transparent mechanisms to trace
information in a peer-to-peer (P2P) network. 6

By combining peer-to-peer networks, cryptographic algorithms, distributed data storage, and a
decentralized consensus mechanism, blockchain technology provides a way for untrusted entities to
agree on a specific state of things and to record this agreement in a resilient, accountable manner
and able to inspect the scheme when needed. Figure 1 illustrates a simplified data structure and the
main elements in a blockchain.

Figure 1: Simplified data structure

As an expected immutable chain of records, the first block in a Blockchain, i.e. the genesis block (also
referred to as block 0), plays a key role as the entity providing the service might use it to validate all the
following chain. From this point, every new valid block contains information related to its predecessor,
binding them permanently.

U4SSC: Blockchain for smart sustainable cities 5