# A Novel and Robust Hybrid Blockchain and Steganography Scheme
## 3 Methodology and Proposed Method
### Proposed Ozyavas-Takaoglu-Ajlouni (OTA) Algorithm
#### 3.3.1 OTA-Steganography Algorithm
Most importantly, the OTA coin is distributed free of charge to the nodes that have been granted access so that the system cost is limited only by the hardware processing power provided by the nodes. Developing the OTA-chain algorithm from scratch allowed many needed features to be added to the system at the beginning. The block structure of the proposed system that meets steganographic needs contains sender address, receiver address, timestamp, last hash, hash, nonce, difficulty, URL, and data. * Sender and Receiver Addresses: 256-bit unique addresses of the sending and receiving nodes in the blockchain system. * Timestamp: This is the date and time information created when a transaction is performed. * LastHash: In the blockchain, the hash value of the last block created, excluding the genesis block, is called lasthash. It is a 256-bit value, calculated with the SHA256 algorithm. * Hash: 256-bit value generated using the SHA256 encryption algorithm. Each block has its own hash value and lasthash, which is the previous block's hash value. * Nonce: A 32-bit value randomly generated when creating the block, which stands for Number Only Used Once. The Nonce value is used for the operation of the reward system in our PoW algorithm, in which the miners in the system participate. * Difficulty: The ease of resolution of the PoW algorithm is used to win the block writing right, and the reward is called difficulty. The difficulty level is automatically increased or decreased according to the status of participation in the system. * URL: In the proposed OTA algorithm, cover multimedia are saved in the server for system security, and its URL is kept in the OTA-chain block, which the receiver uses to reach the cover media. * Data: This is the field where the OTA coin information sent on the OTA-chain is kept. * StegoData: This is the 1 kB address array OTP-ciphered stego-data sent over to and stored in blocks of OTA-chain. The OTA-chain block structure is illustrated in Figure 3.

The OTA-chain algorithm proposes a private blockchain system. In this case, undesirable parties who do not have permission to access the system do not have the opportunity to examine the transactions. The transmitted stego-data is encrypted with the OTP algorithm and then recorded in blocks of the system in order to prevent the nodes that are granted access to the system from falling into the hands of undesirable parties or from manipulating the system by a node (insider attack). Nodes have the opportunity to examine only those transactions that take place in the OTA-chain system. The Proof-of-Work algorithm is used as the consensus algorithm in the proposed algorithm. The nodes that make up the system also work as miners. Nodes that get block writing rights are rewarded with 50 OTA coins. Additionally, the minimum transaction price to be performed on the OTA-chain has been determined as 1 OTA coin. Each up-to 1 kB-size transaction uses exactly 1 OTA coin. Stego-data used in the OTA-chain are all 1 kB-CSD-encrypted array produced in the OTA-steganography stage. Thus, the encrypted data is divided into 1 kB blocks, and the number of transactions is how many 1 kB blocks this confidential data contains. The OTA-chain algorithm is an on-chain blockchain system. The information of the data used in the system is recorded in OTA-chain blocks. Picture matrices are not hidden in system blocks, as seen in similar studies, and this saves time and processing power. Additionally, the proposed system does not suffer from the cost caused by the ready-made platforms used in previous studies shown in the literature. In the OTA-chain system, the URL address of the cover multimedia that the buyer needs are securely shared with encrypted stego-data. The block diagram expressing the OTA-steganography and OTA-chain architecture of the proposed OTA algorithm is illustrated in Figure 4.

Figure 3: OTA-chain block structure. ## 4 Results and Discussion

Tests were carried out using an Intel Core i7 7700 HQ processor and 8 GB Ram computer.