# Trusted Third Party Application in Durable Medium e-Service
## 3 The Proposed TTP Application
### The Security Analysis of the Proposed e-Service  
Finally, let us briefly analyze the security aspects of the proposed technique. Note that experimental verification (based on the case-study example) is presented in Section 4 in detail. An important part of the presented approach refers to the security. Blockchain technology offers the prospective property for handling numerous security attacks, as it can disregard the prerequisite of a centralized authority for performing various operations. In the presented technique, users that participate in the transaction verification and validation utilize a structurally distributed database that stores data from all nodes in an encrypted form authorized by various checks; such as Merkle hash tree (MHT), and ECC. The database is distributed; thus, there is a threat of crashing or corruption. Therefore, the transactions are linked together with cryptographic keys and immutable ledgers, which create much more difficulty for invaders towards the manipulation or deletion of the recorded information. According to the current state of knowledge on the application of blockchain technology, many blockchain-based applications are strongly protected from DoS/DDoS attacks due to their decentralized design [36; 37; 38; 39; 40]. Here, all the services are copied and placed on various network nodes. In other words, we want to emphasize that if an attacker disables one node, they will never be able to disable all the other nodes. Also here, using blockchain, we have ensured that all transactions are expensive, which of course discourages the attacker from directing huge transactions. Our approach is to have message replay protection due to the use of blockchain technology [36; 37; 38; 39; 40]. Here all messages are considered to be a transaction. Every transaction is always timestamped, and every transaction has to go through the consensus part to be well thought out and considered legal. Therefore, the attacker will never be able to respond to the messages, because the consensus procedure will discard them. Our approach is also protected against Sybil attack [41]. In our approach, everyone can only have one identity at a time, and each identity will have only one key pair. Each communication message must be signed with the private key associated with this identity. Moreover, our blockchain-based approach requires the validation of all IDs, so an attacker cannot use a fake identity at all. Man-in-the-Middle (MITM) attack is also impossible because there is no single thread of communication to be intercepted. Therefore, by using blockchain technology, our system can be more secure and protected against MITM attacks. Furthermore, authentication and message integrity are perfectly preserved here. The certificate is used by each follower (for the first transaction). Initially, during the first process, the certificate is directed only to valid participants. All exchanged transactions are signed using private keys. As a result, signatures protect the authenticity of each signature and the integrity of the message. In other words, we can say that it guarantees that no one can join the network without a certificate. Moreover, the TTP signs the document with an electronic signature, and additionally applies AES to generate a 256-bit symmetrical key. Such an AES key is used for encryption of the document. Then ISP decrypts all the AES keys using the corresponding private RSA key. So, these cryptographic keys ensure enhanced security in our approach. The data is always stored in an immutable manner using timestamps, public audits, and consensus mechanisms. Furthermore, the IPFS uses the Secure Hash Algorithm (SHA) 256-bit version to generate the 256-bit hash of the document. Moreover, the SHA-256 algorithm guarantees data integrity. These techniques make the proposed approach secure by assuring data integrity and privacy, and make our approach protected from DDoS and MiTM attacks too.