## 5 Experimental Results and Discussion
### Performance and Cost of Video Data Authentication  
We use time latency to evaluate the performance of a data authentication scheme containing six stages. We evaluate the processing time of watermark embedding and extraction. In addition, we also evaluate the end-to-end delays incurred by the data distribution and retrieval stages. The data distribution procedure is divided into two steps: (i) save video frames into the IPFS network and prepare meta-data containing CIDs and Merkel root; (ii) trigger smart contracts transactions to record them on Ethereum blockchain. Similarly, the whole data retrieval procedure contains two steps: (i) call smart contracts to obtain meta-data; (ii) verify Merkel root and then retrieve frames from the IPFS network. We conducted 50 Monte Carlo test runs for each test scenario and used the averages to measure the results.  
Table 3 shows time latency incurred by key steps in the video data authentication process. The watermark embedding loads a cover frame and then hides a binary watermark mixed with features. Thus, the watermark embedding program takes an average of 1.09 s to create a watermarked frame on the owner's side. The watermark extraction loads a watermarked frame and then rebuilds a binary watermark. It takes an average of 0.62 s to verify a watermarked frame on the user side. We use ten sequential watermarked frames (about 110 KB per frame) to evaluate data distribution and retrieval time latency. Data owners (users) simply push (pull) frames through their local peers within an IPFS network. Uploading and downloading data on a DDS system only introduces small delays (about 0.5 s). The latency of recording metadata through smart contracts depends on block confirmation time, which is greatly impacted by the consensus protocol (Proof-of-Work used by our test blockchain network). Thus, it takes about 5.2 s to save metadata on blockchain. In contrast, visiting the local storage of smart contracts and querying meta information on blockchain takes much less time. Although watermark embedding and data distribution cause more delays (6.69 s) than verification (0.68 s), these overheads only occur once during data generation. In addition, our solution demonstrates efficiency in data verification procedures, which is important for scenarios that investigate and analyze large volumes of video data.  
We use gas fees to evaluate the cost of executing data authentication operations on Ethereum. Table 4 provides a summary of the cost incurred by the data authentication scheme. In Ethereum, gas is the fee paid by the user who launches transactions to update state of smart contracts. The amount of gas used for a smart contract transaction depends on the complexity of the transaction. We only evaluate the costs in smart contract deployment and transactions that update smart contracts, like storing \(TX\) and proofs during the data publish stage. Due to the fact that 1 ETH = 1 billion Gwei in Ethereum, we can present the cost in Ether units by dividing the total gas used by 1,000,000,000. Given the approximate exchange rate at the time of writing (1 Ether = USD 2357.76), we convert Ether cost to U.S. dollars.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Gas Used** & **Cost (Ether)** & **Cost (USD)** \\ \hline
**Deploy Smart Contract** & 190,573 & 0.000191 & 0.45 \\ \hline
**Update Smart Contract** & 875,974 & 0.000876 & 2.07 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Cost of data authentication scheme.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Stage** & **1** & **2** & **3** & **4** & **5** & **6** \\ \hline
**Latency** & 1.09 & 0.43 & 5.17 & 0.04 & 0.02 & 0.62 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Latency of data authentication process (Seconds).