## 4 Experimental Evaluation
### Performance Analysis
It  
\begin{table}
\begin{tabular}{l c c c c c} \hline \hline \multirow{2}{*}{**Properties**} & **Forward** & **Access** & \multirow{2}{*}{**Verification**} & **Dynamic** & \multirow{2}{*}{**Multi User**} \\  & **Security** & **Control** & & **Verification** & \\ \hline Scheme [11] & ✓ & \(\times\) & \(\times\) & \(\times\) & \(\times\) \\ Scheme [24] & ✓ & ✓ & \(\times\) & \(\times\) & ✓ \\ Scheme [25] & \(\times\) & ✓ & \(\times\) & \(\times\) & ✓ \\ Scheme [31] & \(\times\) & \(\times\) & ✓ & ✓ & \(\times\) \\ Scheme [33] & \(\times\) & \(\times\) & ✓ & \(\times\) & \is evident from the graph that the search time for all schemes is directly proportional to the number of users. However, compared to [32], both the scheme in ref. [26] and VSSE exhibit greater advantages. **Verification Performance. ** In this section, since the scheme in ref. [26] lacks the verification capability, we only compare the scheme in ref. [32] with VSSE. Figure 7 illustrates the correlations between the quantity of matching files and the storage capacity of the blockchain. As depicted in Figure 7, the storage requirement of the scheme proposed in ref. [32] escalates as the number of matching files increases. When the number of matching files rises from 1000 to 5000, the storage space usage also increases from 76.3 KB to 380.4 KB. This is because the scheme in ref. [32] requires storing the verification information for each file sequentially on the blockchain, and as the number of files increases, so does the required storage space. For VSSE, we only need to store a fixed bitmap index on the blockchain, which contains information about all the relevant files. Therefore, the storage cost of VSSE is hardly affected by the number of files, and our storage cost is much lower than that of the scheme in ref. [32] (e.g., for the number of matching files is 5000, VSSE incurs a storage cost of 13.8 KB, while the scheme in ref. [32] takes 380.4 KB). Moreover, we compare the verification efficiency of the two schemes. Figure 8 illustrates the correlation between verification time and factors such as the length of bitmap index and the count of matching files. In Figure 8a, the verification time of the scheme in ref. [32] is proportional to the number of matching files, and the verification time of VSSE remains nearly constant and is faster than the scheme in ref. [32] in most scenarios (e.g., for the number of matching files is 5000, the verification time of VSSE is 2.5 s, while the scheme in ref. [32] takes 5.4 s). This is because the scheme in ref. [32] requires the computation of verification information for each file during the verification phase, and the number of files directly affects the verification time. In contrast, VSSE only needs to compute verification information for the bitmap index, and the verification time is solely related to the length of the bitmap index, unaffected by the number of matching files. Figure 8b further illustrates the impact of the bitmap index length on the verification time of VSSE. Distinct colors of bars indicate varying numbers of matching files. With the bitmap length increasing from 1000 to 5000, the verification time also increases from 0.53 s to 2.53 s. However, when the bitmap index length is fixed, the verification time remains almost the same. Figure 5: Time of index generation. [PERSON] et al. (2020) refers to the scheme in ref. [32], and [PERSON] et al. (2022) refers to the scheme in ref. [26]. Figure 6: Time of search. (**a**) The influence of the quantity of keywords and the count of matching files on the search time. (**b**) The search efficiency of each scheme under different numbers of matching files. (**c**) The impact of varying numbers of users and matching files on search time. (**d**) The influence of varying numbers of users on the search time for each scheme. [PERSON] et al. (2020) refers to the scheme in ref. [PERSON] et al. (2020), and [PERSON] et al. (2022) refers to the scheme in ref. [PERSON] et al. (2020). Figure 7: The cost of storage. [PERSON] et al. (2020) refers to the scheme in ref.