# A Novel and Robust Hybrid Blockchain and Steganography Scheme
## 3 Methodology and Proposed Method
### Blockchain: An Overview  
Blockchain technology is the second technological development with a similar effect on our lives after internet technology, and its impact continues to increase day by day. Blockchain technology has been introduced as the creative power of Bitcoin crypto money in response to the need for a system with a high level of transparency and anonymity to prevent misleading information from central authorities. Blockchain technology can be described as a distributed database. Similarly, it is also called distributed ledger technology. Because the blocks that make up the blockchain are accepted by the nodes that make up the system to record the transactions performed, and the current transaction records are available in all nodes, distributed ledger technology is ascribed. As the name suggests, all transactions carried out in the blockchain system are recorded and stored in blocks, just like the pages of a ledger. In this context, the blockchain system works like a ledger. However, this ledger is not stored in a single location but in all nodes that make up the blockchain. This way, targeting the database cannot be a realistic goal. As a result of this feature, blockchain systems have a high level of data security [39]. In the case of Bitcoin, it is the nodes that make up the system transfer crypto money between each other. The Bitcoin blockchain platform is a public blockchain. In other words, anyone who wants to join the system can become a participant as a node and examine all the transactions that have taken place since the first block. In the Bitcoin blockchain, the nodes are anonymous; that is, the affiliation of the nodes is unknown. Each node has a wallet, and this wallet has two keys. While the public key is the publicly known address of the node, the private key is the private key of the node owner to access the system. If the private key is lost, access to the system is not possible. Nodes can send Bitcoins to each other peer-to-peer through these wallets without the need for any third party. In this context, blockchain systems have a decentralized structure [40]. The most basic unit that makes up the blockchain is the blocks. Except for the first block, the genesis block, all blocks have two hash function values. One of them is the previous block's hash value, and the other is the hash value produced in its block. Hash functions are cryptological algorithms that work unidirectionally and give you fixed results. Today, secure hash algorithm SHA256 is a widely used algorithm that produces 256-bit values. It will be seen that the hash value changes as a result of the slightest change in the data used in the calculation of the hash value. This feature ensures that the transaction records recorded in the blockchain cannot be changed, thus providing a high level of security. The secure system, obtained by connecting the blocks using hash values, brings a tamper-proof feature to the blockchain. The Bitcoin blockchain database is accessible to the public, expressed in the Bitcoin example, and is not a condition that must be used in all blockchain solutions. Public blockchains are generally preferred in applications where the participation of cryptocurrencies or the entire society is expected. On the other hand, private blockchains [41] are frequently preferred in cases where privacy and access are desired to be limited. Blockchains, which are designed to be integrated into hospital systems, are the preferred models of the digital services offered by states to their citizens and are implemented with blockchain technology. Here, access to the system is authenticated, and it is determined beforehand who can see how much data and what actions they can take. The use of private blockchains will have significant advantages in studies requiring data security and blockchain technology [42]. In blockchain systems, those who record data in blocks are called miners.