Blockchain the reader understand the present research

    Blockchain is a technology developed to allow trustless sides to make transactions, without the need of a third-party organization. To achieve transparency in transactions, it uses a public ledger accessible to all participants, where the absolute majority decides for the validation of a transaction. The blockchain technology was introduced in 2008, but closely after it became widely known as it provided the infrastructure for a cryptocurrency payment system, Bitcoin 1.

    Since then, Blockchain has gained great interest in several research areas mainly because it provides absolute anonymity, satisfactory security, without any centralized control of the transactions and data. The great significance lies in the fact that every infrastructure and application can now run without any intermediary and succeed in terms of functionality and certainty.    Although research is in early stages, real time applications in large scale are already making their appearance. The New York state 2 has developed a blockchain-based community-powered microgrid in Brooklyn. This means that neighbors are buying and selling energy to one another through o blockchain platform. Furthermore, in Austria, the largest energy supplier, Wien Energie 3, is participating in a blockchain pilot project for gas trading. In another sector, a global startup company, Everledger 4, is using a blockchain application, smart contracts and a digital ledger to track and protect valuable assets, such as diamonds.     Large scale projects like these mentioned above, have triggered an explosion of interest in blockchain research.

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The main reasons behind this are the two essential properties of blockchain technology: anonymity and security. In Internet of Things (Iot) communication networks for example, all IoT devices of a same network could compose a blockchain network. Digital content providers and distributors could exploit smart contracts to support a new infrastructure. In Software-Defined Networks (SDN), the network control and forwarding could also be achieved through blockchain technology. Intelligent (or self-driving) vehicles technology still faces many issues in trust and reliability of data sharing, that could likely be resolved using blockchain as a back bone of their data sharing environment.    The objective of this work is to provide an overview of where the current research regarding blockchain is, mostly in the field of network infrastructures. Our goal is to help the reader understand the present research and thus emerge new use cases for Blockchain technology.

  Fig. 1. An example of blockchain processesII. BLOCKCHAIN OVERVIEW    Blockchain is an innovative approach in distributed data structures, as it is replicated and shared across every network member.

It is an actual “chain”, a virtual one, consisting of blocks that keep records and timestamps of all past activities.    As mentioned above, a blockchain is completely open to anyone. Its most interesting property is that once some data has been recorded inside, it becomes very difficult to change it. To clarify this, let’s take a closer look at a block. Each block contains data, the hash of this block and the hash of the previous block. The data that is stored inside a block depends on the type of blockchain. It could be anything, from money and IP Addresses to video and position of self-driven vehicles.

A block also has a hash. A hash can be compared to a fingerprint, as it identifies a block and all of its contents and it is always unique. The hash for a block is being calculated once the block is created.

Changing something inside a block, will cause its hash to change. So, it becomes clear that hashes are very useful for data modification detection. The third element inside each block is the hash of the previous block. This effectively creates a chain of blocks and it is this technique that makes a blockchain so secure.   Block0 Index, Timestamp, Data, Hash, Previous Hash     Block1 Index, Timestamp, Data, Hash, Previous Hash     Block2 Index, Timestamp, Data, Hash, Previous Hash             Fig. 2.

An example of blockchain processes    As you can see in Fig. 2, each block has a hash and the hash of the previous block. So, block number 3 points to Block number 2 and so on. Now the first block is a bit special because it has no previous block to point to. It is called the genesis block.

In case someone tries to tamper with a block, its’ hash changes as well. In turn that would make all following blocks invalid, because they no longer store a valid hash of a previous block. But using hashes is not enough to prevent tampering.

    Computers and IoT devices nowadays can calculate hundreds of thousands of hashes per second. So, someone could effectively tamper with a block and recalculate all the hashes of other blocks to make this new blockchain valid. So, to mitigate this, blockchains have something called Proof-of-Work (PoW).

It is a mechanism that slows down the creation of new blocks. In Bitcoin it takes about 10 minutes to calculate the required PoW and add a new block to the chain. This mechanism makes it very hard to tamper with the blocks, because if someone tampers with one block, they’ll need to recalculate the PoW for all the following blocks.

    The creative use of hashing and the PoW is main source of blockchain’s security. But there is one more way that blockchains secure themselves and that is by being distributed. Instead of using a central entity to manage the chain, blockchains create a peer-to-peer (P2P) network that anyone is allowed to join.

When someone joins the network, they get the full copy of the blockchain. The node can use this to verify that everything is still in order. Therefore, to successfully tamper with all blocks on the chain, someone needs to redo the PoW for each block and take control of than 50% of the P2P network. This is almost impossible to be done, mostly due to the power cost and computational time.

   Fig. 1 demonstrates the processes that take place during a Blockchain transaction. ?n the general case we can say that the transaction takes place in 6 basic steps: 1)       First off, a node requests a transaction.2)       This request is then broadcasted into the rest of the nodes that form a peer-to-peer (P2P) network. The nodes could be computers, IoT devices, ad hoc sensors, etc.

3)       The peers decide through majority about the validation, considering the transaction and the user’s status.4)       Once verified, the result of this negotiation is combined with all the previous to create a new block of data for the common ledger.5)       The new block is then added to the existing chain. The algorithms used to add new blocks ensure that no valid insertions can be removed.6)       And so, the transaction is completed.

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