# Rentable CDN Using Blockchain and Proof of Provenance
## 5 Conclusions  
Consumers are downloading and uploading contents more than ever, but there are almost no small or medium scale content providers due to the high initial risk associated with developing a content distribution network (CDN).  
Rentable CDN provides an alternative way to distribute contents then the traditional CDN and decentralized CDN. It uses Blockchain to decentralize the payment process and p2p communication for transferring the content between the users. Since the payment is decentralized, all payment operations are transparent. The contents are transferred using the hardware already owned by users to reduce the initial hardware investment.  
Collusion attack is one of the main concerns when operating a p2p based CDN. This is due to lack of robust verification method by a third party to check whether a content has been transferred from a user to another user. Thus, malicious users can use variety of collusion attacks to get paid for the services that they did not provide and reduce the content transfer speed. Existing work tries to make collusion attacks difficult by putting constraints on how content is transferred and penalizing malicious users to discourage collusion. Even though the loss due to collusion per content is small, the attacks are easily scalable and reduce the content transfer speed significantly. To demonstrate the scalable collusion attack, we simulate the collusion attack and compare the existing work with the proposed method. The simulation results show that Downloaders download the content faster, and do not incur loss due to collusion when the proposed method is used.  
The proposed method protects against collusion attacks using the proof of provenance. Proof of provenance tracks which Uploaders can upload specific contents, and penalize Uploaders and Downloaders based on that information. Compare to the existing work, the proposed method provides faster download speed and is not vulnerable against scalable collusion attacks. It is also secure against replay attacks that try to claim previously claimed proof of piece to get paid again without doing the work. This is achieved by designing proof of piece to be unique with respect to the content contract.  
To conclude, the proposed method provides faster download speed than existing work while being secure against scalable collusion attacks that existing p2p based CDNs are vulnerable against.  
**Author Contributions:** Conceptualization, S.K., V.S., and H.J.K.; methodology, S.K.; software, S.K.; validation, S.K., V.S., and H.J.K.; formal analysis, S.K.; investigation, S.K.; resources, S.K.; data curation, S.K., V.S., and H.J.K.; writing--original draft preparation, S.K.; writing--review and editing, S.K. and V.S.; visualization, S.K.; supervision, V.S. and H.J.K.; project administration, S.K.; funding acquisition, S.K. and H.J.K. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was supported by an Institute for Information & communications Technology Promotion(IITP) grant funded by the Korea government (MSIP) (No.2018-0-00365, Development of on-off hybrid blockchain technology for real-time large-scale data distribution).  
**Conflicts of Interest:** The authors declare no conflict of interest.