## 5 Image Chain (_i_Chain) to Prevent False Image Injection Attacks  
In recent times, blockchain has been investigated by a number of researchers [19; 20; 21; 22]. The common finding is that blockchain is helpful for healthcare domain security and privacy along with other applications. However, specific attacks such as false image injection attacks have never been addressed. Therefore, inspired by the effectiveness of this emerging technology, in this paper, a blockchain based remedy for false image injection attacks is proposed. Figure 5 reflects the conceptual framework of the proposed **iChain** approach to prevent false image injection attacks. The fundamental idea behind this approach is to use the blockchain technology as discussed in the previous section. Since, this paper is trying to establish the concept of false image injection attack prevention using blockchain technology, the classification of the blockchain is treated as part of future works. Blockchains are classified into three major categories [23] as follows: public, private and hybrid. All parties can read, and write in public blockchains. In private blockchains, specific individuals are allowed to participate in the verification process. Hybrid blockchains can be customized based on the combination of private and public chains. Sensitive medical images should be stored in a blockchain network to avoid any consequences of false image injection attack. Once the images are stored using blockchain, if an attacker tries to inject false images, all the parties in the blockchain network must agree otherwise it is impossible to make any changes. In case of the example shown in Figure 5, there are three parties in the network, doctor, patient and family members who all should agree to approve any changes in the medical images stored in the blockchain based medical image repository. The **iChain** framework (Algorithm 1) reflects the backbone of the proposed framework. Additionally, blockchain saves data in hash functions with time stamps, it is highly unlikely to be tampered with or to have any chance of being misled by false image injection attacks. Unlike other cryptographic techniques to secure data, such as AES, DES, and RSA algorithms, blockchain requires a validation stage, i.e., agreement among all parties involved. This unique characteristics enforces the integrity and effectiveness of the data being stored in a blockchain framework. ```
Begin A new image needs to be added/modified in the repository The image is broadcasted to all parties ifAll parties agreethen Add the image or approve the modification; else Ignore the change end end
```  
**Algorithm 1**_i_Chain AlgorithmFigure 6 reflects the underlying mechanism of the proposed framework. The first part of the figure shows a sample of **N** blocks in the image chain. It is shown that the hash values are stored in each block for both the current and previous blocks. Let us assume that an attacker injects a false image in Block 2. Once the image data is changed, the corresponding hash value will also change. However, Block 3 in this blockchain contains the original hash of Block 2. At this stage, due to the mismatch of hash values in the **iChain**, all the associated blocks are considered tampered with for not having the correct hash of the previous block. Thus the false image injection attacks can be prevented by the proposed framework. In terms of the usage of hash algorithms, based on the computational efficiency of MD5, SHA-1, SHA256, or SHA512. can be chosen. Although, blockchain based solutions are widely accepted for a variety of applications, they are still struggling to ensure security despite their promising characteristics [24]. Blockchain systems can  
Figure 5: Conceptual framework of **iChain**. Figure 6: Underlying mechanism of **iChain**. be found vulnerable and there is a trade-off between scalability and security. Since blockchain based systems are quite new, there is a significant lack of research to address the scalability issues in an blockchain environment.