## 4 Results: Threat Analysis
### Threat 2: Intentional or Accidental Misconduct by Users  
The framework gives users the flexibility to generate their own transactions, but it relies on their responsible behavior to maintain system integrity. Misconduct, whether intentional or accidental, can lead to inconsistencies, execution failures, or denial-of-service risks. The proposed framework addresses these concerns through the following mechanisms:  
* **Dependency Validation Responsibility:** Users are required to construct transactions based only on data from finalized transactions whose hash values have been recorded in a platform chain segment already anchored to the main chain. If a user references unconfirmed transactions that later fail, the resulting transaction is invalid and the responsibility lies entirely with the user. This rule prevents accidental inconsistencies and protects the platform from reliance on unguaranteed outcomes. * **Double Selling:** Double selling refers to an attempt by a user to sell the same digital asset to multiple recipients before the completion of the first transaction. Consider a case where a user \(u\) attempts to sell the same digital asset \(D_{K}\) to both \(v\) and \(w\), by submitting the transaction \(tx_{1}\) as in (9) to transfer \(D_{K}\) to \(v\), while simultaneously initiating another transaction \(\widetilde{tx}_{1}\) to transfer \(D_{K}\) to \(w\), before \(tx_{1}\) is finalized. In the proposed framework, both \(tx_{1}\) and \(\widetilde{tx}_{1}\) can be registered successfully, since neither \(D\) nor \(t_{M}\) checks transaction dependencies during the registration phase. However, transactions are executed one at a time in the order they were registered. For each transaction, the smart contract \(sc_{P}\) first validates its inputs, such as ownership and predefined execution conditions. Only if the transaction is valid is it executed. Therefore, once \(tx_{1}\) is successfully executed and \(D_{K}\) is transferred to \(v\), the subsequent transaction \(\widetilde{tx}_{1}\) fails the validity check because \(u\) no longer owns \(D_{K}\). Since the invalid transaction originates from \(u\)'s misconduct, \(sc_{P}\) does not refund the execution cost \(\eta\) that \(u\) paid to invoke \(\widetilde{tx}_{1}\). Instead, the smart contract redirects this cost to compensate \(w\), assuming \(w\) has already initiated a payment transfer as in (13) based on the expected receipt of \(D_{K}\). To enable this compensation, the framework requires that \(\eta\geq 2\epsilon\), where \(\epsilon\) is the execution cost of the _coin_ transfer on the reference chain \(\mathbb{R}\mathbb{C}\). This design ensures that the fee collected from \(u\)'s invalid transaction is sufficient to cover the refund cost to \(w\), while leaving no incentive for \(u\) to exploit the system. Bysetting the execution fee for asset transfer contracts higher than a standard _coin_ transfer, the framework effectively deters malicious users from attempting double selling. * **Replay Attack:** A replay attack occurs when a malicious actor attempts to reuse a previously submitted and valid transaction in a different context or time, aiming to duplicate its effect. In blockchain systems, such attacks can lead to unauthorized asset transfers or contract invocations if proper safeguards are not put in place. In the proposed framework, replay attacks are prevented by including a unique nonce in each user-generated transaction, as shown in (9). This nonce ensures that each transaction is executed only once and cannot be validly replayed in the future. If a transaction with the same nonce is submitted again, it will be rejected by the smart contract as a duplicate. This mechanism guarantees transaction uniqueness and defends the system against replay-based exploits. * **Payment Refusal:** A potential threat in digital asset transactions arises when a buyer refuses to complete payment after initiating or receiving a transaction.