# Secure Delivery Scheme of Common Data Model for Decentralized Cloud Platforms
## 3 Results
### Performance Evaluation  
By using IPFS to store files, the CDM cloud can provide a repository for CDM files with a method of persisting their CDM. When a CDM file is added to an IPFS node, the node returns a hash value of Content-Identifier (CID) for the CDM. The CID is the direct result of running the file through a cryptographic hash function. Every unique file will have a unique CID. This allows someone to retrieve a particular piece of content by providing the CID of the desired files. When a node is connected to the IPFS network, the content of that node is frequently broadcasted over the IPFS Distributed Hash Table (DHT). IPFS nodes treat stored data like a cache, meaning there is no guarantee that the data will continue to be stored, unless the CID is pinned. In this experiment, CDM files imported into the SC-CDM are stored and shared in IPFS. Therefore, in order to evaluate the IPFS storage performance according to the size of the CDM file, the storage processing performance is examined according to the file size. When the IPFS node retrieves data from the network, it keeps a local cache of the data for future usage and takes up space on that particular  
Figure 11: The overall process for building a secure CDM in SC-Blockchain. IPFS node. The used files for writing the CDM are designated to have the size of 1 KB, 10 KB, 100 KB, 1 MB, and 10 MB. Figure 12 presents the elapsed time for writing to IPFS that is linear with the file size. The fact that the elapsed time is greatly increased in a 10 MB file is explained by the characteristic that appears because IPFS stores blocks in units of 256 KB. In the case of 1 MB, four blocks are written, but in the case of 10 MB, the size of the block increases by 10 times to 40 blocks. In other words, since 1, 10, and 100 KB are stored in one block, it can be understood that there is little difference in write execution time. The SC-CDM's data analysis is processed by using the analysis tools inside the SC-CDM. Registered researchers are required to access CDM materials for this purpose, and researchers using CDM perform IPFS node access that operates inside the SC-CDM. This differs from the way the current CDM delivers and operates data to remote researchers. In this case, researchers perform this experiment in terms of the performance of SC-CDM, which analyzes data through access to data within the SC-CDM. This experiment composes a swarm cluster with private network function after registering two IPFS nodes as peers, to show the benefits of CDM data access of SC-CDM. To evaluate the performance of the configured swarm cluster, the elapsed time of operation execution is measured by accessing the CDM data of the local IPFS node inside the SC-CDM. In addition, to evaluate the data-access elapsed time of the existing CDM operation method, the execution time of the CDM data-access operation in the remote IPFS node was compared. The elapsed data-access time of the remote IPFS node was to ignore network delays for objective performance evaluation. To this end, after passing the hash value to read data to another peer of the swarm cluster, the elapsed time of CDM data for data access was obtained. The file is used for file accessing and is designated as the size of 1 MB, 10 MB, 100 MB, 200 MB, 500 MB, 750 MB, and 1 GB. After writing 20 consecutive times, leverage the elapsed time average and standard deviation of the execution time are determined, obtained as an experimental result. Table 4 presents the evaluation of accessing CDM data from IPFS in a swam cluster. Figure 12: Evaluation of the elapsed time writing to IPFS. Figure 13 shows the standard deviation of elapsed time and elapsed time (blue line) when CDM clients access the SC-CDM local IPFS node. In the traditional CDM environment, CDM clients showed standard deviation of elapsed time and elapsed time (yellow line) when accessing remote IPFS nodes. As shown in Figure 13, the elapsed time of data access of local IPFS and remote IPFS increases relatively as the size of CDM data increases.