Carleton University - School of Computer Science Honours Project
Summer 2021
Threshold Cryptosystem Scheme: Secure Delegation Through the Distribution of the Private Key Across Multiple CDN Servers
Tan Tran
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ABSTRACT
Content Delivery Networks (CDNs) improve the performance and security of web sites. They are used to reduce the latency of web access by redirecting the user to a surrogate server close in proximity, as well as to lighten the load of original web servers. A CDN is usually composed of many surrogate servers distributed all around the world. If a web site uses the CDN service, a subset of the surrogate servers in the CDN will replicate that web site’s content. When users access the web site, they will be directed to the CDN and finally get the content from a nearby surrogate server rather than the web site’s origin server. To provide a higher level of security against attacks, CDN’s may also use a threshold cryptosystem scheme. A threshold cryptosystem is a cryptosystem that protects information by requiring some subset of surrogate CDN servers to authenticate itself through a TLS connection before any data is sent to the client. The objective of this project is to implement a crypto-thresholding scheme, where a CDN's private key would be split across multiple CDN surrogate servers. The project goal would be to allow secure delegation through the distribution of the private key across multiple servers and analyze the relationship between usability and security by measuring this time through varying simulations. A consensus then must exist among a threshold group of servers to sign a transaction (typically a TLS transaction) for authentication (concatenate the private key). This way, if part of the key was leaked, or one server got compromised, the attacker won't be able to act on its own to terminate a TLS session. This implementation can then be used by CDN providers in deploying secure TLS delegated credentials to the end-user from the hosted server.