A blockchain is a timestamped series of immutable transactions that are managed by a cluster of computers using special computer algorithms. These immutable records are not owned by any single entity. A blockchain is a decentralized P2P network of nodes. Each node in a blockchain shares the same copy of data, also called the digital ledger. Each node present in the network uses the same algorithm to reach a consensus.
This article is an excerpt from the book Mastering Blockchain Programming with Solidity by Packt Publishing, written by Jitendra Chittoda. This book covers insights about maintaining code quality with different tools, a basic understanding of blockchain and much more. In this article, you will learn basics about blockchain, its properties, and much more.
The ledger can record transactions between two parties in a verifiable and permanent way. Whenever there is a change in the ledger using transactions, changes are distributed to all the nodes, to verify and update their own copy of the ledger.
Each computer that participates in this P2P network is called a node. Each node maintains the records of transactions in multiple consecutive blocks. The P2P network is also used in torrents such as BitTorrent; however, torrent networks are not like blockchains, as they are designed to shares files only.
Blockchain technology is also called Decentralized Ledger Technology (DLT), as each node in the network keeps the same copy of the ledger. Please have a look at the following diagram:
Chain of connected blocks
In the preceding diagram, each block is connected with a link (also known as a chain). The chain is usually recognized as the chain of all the blocks. The link between two blocks is implemented by having a record of the cryptographic hash of the previous block in each block so that you can visit the chain in reverse chronological order.
It is extremely hard to reverse a blockchain transaction. However, there have been cases when a 51% attack allowed an attacker to double-spend coins. One such example is when Ethereum Classic (symbol: ETC) was attacked with a 51% attack, in which approximately $1.1 million worth of ETC was lost.
Blockchain solves the double-spending problem
As we know, we can share documents and pictures over the internet with someone. When we share those documents or pictures with another person, we actually share a copy of the file. Once that copy is sent to another person, you and the other person have the same copy of that document.
However, things such as money, bonds, and shares must not be shared as copies, as we do for documents/pictures when we need to transfer them over the internet. If you try to send money P2P, without using any intermediaries, then both parties end up having the same copies of the money. This is called the double-spending problem.
For example, if Alice gives a $10 bill to Bob, then Alice must not hold a copy of the $10 bill, as it’s given to Bob. These are called value transfers. To transfer those items that have values over the internet, we need to depend upon Trusted Third Parties (TTPs).
Banks and stock exchanges are the TTP on which we rely for transferring values (money and shares) from person A to B. For value transfers between two parties over the internet, they both have to depend upon a trusted middle party (centralized) to process the transactions and ensure the safety of transactions.
Blockchain solved this double-spending problem. Now, for value transfers between two parties, neither of them have to depend upon a middleman (trusted party). They both can do safe transactions directly. Blockchain’s decentralized network and consensus algorithm ensures the safety of transactions and prevents the double-spending problem.
Properties of blockchain
Blockchain has properties of both decentralized and distributed networks. Using those types of networks along with cryptography adds more properties. We are covering properties related to the Ethereum blockchain rather than other blockchain implementation properties. The other blockchain implementations might have different properties. Let’s discuss those properties.
1) Distributed ledger
Multiple nodes make up a distributed blockchain network. All nodes share a common ledger, where records of transactions are kept.
2) Fault tolerance
A blockchain network is distributed and each node maintains the same record of the ledger. Even if some nodes in the network are corrupted or go down, it can continue operating safely up to a certain limit, as well as processing transactions with running nodes.
3) Attack resistance
A blockchain network does not have centralized control. The network’s resistance to attacks is maintained by the miners who are putting their processing power (using nodes) into use to guard against malicious attacks. These miners earn some incentives to keep the network safe by behaving honestly. This is done by using the distributed network and cryptographic techniques.
4) Remove intermediaries
Blockchain technology removes the dependence on TTP/middle parties/intermediaries. Using blockchain technology, a transaction can be done directly between two entities/systems. In place of intermediaries, we can place blockchain systems.
5) Consensus protocol
This is a protocol that ensures that all nodes participating in the network ensure the safety of the network. All nodes use a consensus protocol (a specific algorithm) to reach a consensus and discard the blocks generated by the attacker/bad node, to avoid catastrophic system failure. For example, Bitcoin and the Ethereum blockchain, at the time of writing, work on the Proof-of-Work (PoW) consensus protocol.
Ethereum uses the Ethash PoW consensus algorithm, which is Application Specific Integrated Circuit (ASIC) resistance. In the future, Ethereum will switch its consensus algorithm from PoW to Proof-of-Stake (PoS).
The PoW protocol is a consensus algorithm in which nodes compete with other nodes to solve a cryptographic puzzle. The node that solves the puzzle first adds a new block to the blockchain (called mining). By doing this, they also earn some block reward in the blockchain’s native coin.
The PoS protocol is a consensus algorithm in which a person has to put the native blockchain coin up for stake (lock). The protocol selects a miner randomly or according to coinage. The miner is rewarded when the block added is valid, otherwise, they may lose their stake.
6) Faster settlement
Traditional banking systems can be slow in some cases, as they need additional time for processing a transaction; for example, cross-border payments. However, with blockchain technology, there are no intermediaries; therefore, the transaction happens directly between entities and the settlement is much faster, compared to traditional systems.
7) Lower transaction fees
Using the traditional banking system, doing cross-border payments is costly. The intermediaries take their commitment to process the transaction between two parties. But by using blockchain technology, the cost of doing transactions is significantly lower because we can remove the intermediaries and perform the transactions directly.
Some blockchain systems maintain transparency. Ethereum is a public blockchain network. All the transactions of the Ethereum blockchain are public and transparent. Anyone can see the balance and transaction history of any wallet at any time, just by accessing the Ethereum public blockchain via a block explorer. However, some work toward having privacy on the Ethereum blockchain is being done; for example, using the AZTEC protocol.
Every transaction that happens on the Ethereum blockchain is immutable. Smart contracts on the Ethereum blockchain are also immutable. Once the smart contract code is deployed, it cannot be changed. Smart contract code will remain on the blockchain forever. Anyone can see any deployed smart contract any time in the future as well, just by putting its contract address on the block explorers. Data that is being stored in smart contract variables is also immutable unless there are data removal techniques that have not been exposed by the contract code.
Also Read: How Blockchain Will Rebuild the World
10) Irreversible transactions
Once a transaction is executed on a blockchain and it receives sufficient confirmation, the transaction becomes irreversible. The irreversible transaction ensures the safety of the value transfer. The higher the number of confirmations received for a transaction, the harder it becomes to reverse the transaction from the attacker.
11) Artificial trust
When replacing trusted middle parties (intermediaries) with blockchain technology, I call it artificial trust. Blockchain technology will be trusted while doing P2P transactions. A person only has to trust the blockchain technology that is going to execute their transaction.
12) Trustless systems
Two people, without knowing each other, can do transactions using blockchain technology. They do not have to trust each other, they only have to trust blockchain technology. For both persons, it is a trustless system.
Centralized systems sometimes have to go through regular maintenance and downtime, resulting in inconvenience to the users. The blockchain is decentralized, so even if some nodes go down/are corrupted, the network will continue to function and will be available to process transactions 24/7.
14) Empower individuals
Each individual entity/person has their own wallet’s public and private keys on the blockchain network. Using those wallets, they are in full control of their assets and the privileges available for those wallets. Blockchain assures that the ownership of a person’s data is in their hands.
However, an individual can only maintain full control over their cryptocurrency or data when they own the private keys of their wallet. When the private keys of their wallet are maintained by another entity, such as centralized exchanges, they may not have full control.
A wallet is a software that keeps one or more cryptographic private and public keys. Using these keys, you can interact with different blockchains and are allowed to send and receive digital currencies. You can also interact with smart contracts using any of the accounts present in your wallet.
16) Chronological order of transactions
Blockchains keep their transactions in blocks. Multiple transactions are coupled together and stored in a new block. Next, that new block is appended to the chain of previous blocks. This keeps all the blockchain transactions maintained in chronological order.
Every transaction on the blockchain is stamped with the current time. This enables the blockchain to maintain all the transaction histories of an account. Also, this can be used to prove whether or not a transaction happened on a certain date and at a certain time.
18) Sealed with cryptography
Asymmetric cryptography is used for wallet generation and transaction signing using the Elliptic Curve Digital Signature Algorithm (ECDSA). All transactions are packed together using the Merkle tree and SHA-256 cryptographic algorithms. This makes blockchains secure and reliable to use.
When not to use blockchain
Use blockchain technology as a tool for the development of specific scenarios. As we have seen in previous sections, blockchain technology can solve some problems where you want to replace an intermediary/middleman/TTP and do P2P value transfer transactions. This also includes problems where it is possible to replace existing trust with software-defined trust, using smart contracts.
You should not use Blockchain to replace your existing database. If your specification requirements can be solved with other software tools and techniques, then you should use those only. If there is no requirement for blockchain in your system architecture, avoid using it.
For example, you do not need blockchain when building very high throughput, latency-critical transaction processing systems. However, when blockchain technology improves in terms of high throughput in the future, and you need some of the previously discussed properties of blockchain in your system, it would be a wise decision to use it.
Blockchain depends on off-chain oracles
On their own, a blockchain is a separate network. It uses P2P networking over the internet to keep sharing transactions between nodes, but it does not have a way to get the data from outside (such as any data present on the internet, other than blockchain data) of the blockchain network, also known as off-chain data.
For example, the Ethereum blockchain cannot fetch any data from the internet on its own. There are some third-party-developed Oracle services; by using them, you can fetch the data from the internet to the blockchain and do your transactions.
If your application is highly dependent upon third-party data available on the internet, then you should not use blockchain. If your off-chain data requirement is small enough, then you can use Oracle services and do your transactions on the Ethereum network. For example, when you just need currency version rates from the internet, you can use Oracle services.
When you are building a decentralized application on a public Ethereum blockchain and require off-chain data, you can use Oracle services such as Oraclize or ChainLink.
When you are building private applications using a private Ethereum blockchain and require off-chain data, you can write your own Oracle service application to read the data from off-chain. You can write your own Oracle to read some private data (such as data that’s internal to the company) as well.
You can set up your own private Ethereum blockchain on your private network. This private blockchain will not be connected to a public blockchain. You can customize your private blockchain according to your needs. However, applications deployed on a private blockchain would not be treated as purely decentralized applications.
In this article, you learnt the basics about blockchain, its properties, and much more. To know more about blockchain and Ethereum, check out the book Mastering Blockchain Programming with Solidity by Packt Publishing.