# Mobility, Citizens, Innovation and Technology in Digital and Smart Cities
## 3 Cities Transportation Trends
### Blockchain for Managing Cities' Transportation Data and Contracts
#### 3.5.1 The Core of the Blockchain and Smart Contracts  
The Blockchain technology has been gaining attention since the appearance of Bitcoin cryptocurrency [159]. Despite hype applications on the financial sector, other vertical markets have been trying to integrate its features for different assets' management. To satisfy different business needs, several Blockchain platforms have emerged concomitantly with solutions presented by other distributed ledgers' technologies (DLTs) [160, 161, 162, 163]. At a glance, the blockchain is a distributed network with enhanced security attributes, in which the P2P architecture and cryptographic keys compose a protocol that keeps the network reliable through automatic verification processes. One of its distinguishing characteristics is how the protocol reflects the way the network behaves when a new operation is requested. For this end, the consensus algorithm is responsible for managing who should append new values on the distributed database (ledger) and the possible conflicts that might arise. Another feature is that any interaction with the platform is designated as a transaction and is recorded on a new blockchain state. Smart contracts are algorithms designed for being interpreted by specialized virtual machines, throughout its conversion to opcodes. Those virtual machines, usually, specifically designed for each blockchain project, often call precompiled scripts that optimize the calculus of commonly used functions. After being registered throughout a transaction, they are identified by a unique hash. In fact, in Bitcoin, NEO Blockchain and several other blockchain projects, the standard addresses that we often see are all smart contracts with a simple functionality of pushing a set of bytes and calling an opcode often known as a witness checker. This allows the creation of distributed applications (DApps) to serve different business demands [164, 165]. However, Blockchain follows a long time evolution of distributed protocols' technology. Section 3.4 highlighted decentralization via MAS, which has inspired the solutions focused on the Byzantine Fault Tolerance (BFT) problems [166], discussed around the 1980s, and currently integrates important aspects of Blockchain consensus. Some Byzantine-like variations have been discussed over the years. For instance, the Practical BFT protocol [167] is celebrating 20 years now, and its outcomes have inspired Blockchain world consensus such as the Delegated BFT used by the NEO Blockchain [160]. Moreover, blockchains are also recognized by different network governance levels that imply how the ledger read/write access is made. This gets a classification from permissioned to permissionless, i.e., from more centralized to decentralized network, and it is used to compose a range of Blockchain platforms. Besides the more well known such as the NEO, EOS, Ethereum, and Bitcoin, there are other relevant platforms that focus the most on industrial applications of permissioned chains. Among them, we highlight that the NEO Blockchain is a pioneer high-performance library for developing smart contracts. It was the first Blockchain project to successfully run a public chain with the finality of one block. This means that information appending is finalized as soon as the majority of those involved in the consensus signed the information. The diverse platforms available meet specific business application needs [168]. As a result, there are several DApps under development that cover the future transportation system, the electricity grid, and a variety of other service applications. For instance, considering smart grids [169], it is possible to manage Electric Vehicle (EV) recharging stations of different energy suppliers through a standard method of payment [170], in which the flow of money and service (the core of the IoV) would flow according to predefined rules.