Studies on Verifiable Secret Sharing.

Date of Submission

December 2011

Date of Award

Winter 12-12-2012

Institute Name (Publisher)

Indian Statistical Institute

Document Type

Master's Dissertation

Degree Name

Master of Technology

Subject Name

Computer Science


Applied Statistics Unit (ASU-Kolkata)


Gupta, Kishan Chand (ASU-Kolkata; ISI)

Abstract (Summary of the Work)

In this Thesis we will discuss three important tools in cryptography namely, Secret Sharing, Verifiable Secret Sharing and Weak Secret Sharing. In all secure systems that use cryptography in practice, keys have to be protected by encryption under other keys when they are stored in a physically insecure location. But the keys used for protection have to be protected themselves, so no matter what we do, we cannot avoid having one or more keys in our system that are only protected because they are stored in a physically secure way. These are typically very high priority keys, such as the secret key that a certification authority (CA) uses to create certificates. Precisely because such a key is so important, it would be a disaster if it was revealed to an adversary. But it would be equally bad if the key was lost and could not be retrieved. In other words, there is a big need to keep such keys secret and available at the same time.This seemingly puts designers of security systems in a rather difficult dilemma: to make sure that a key is not revealed to anyone, one is inclined to store it only in a single, very secure location; while the need to make sure the key is always available seems to imply that you should store the key in as many different locations as possible. Secret sharing is a technique that allows us to nevertheless address both of these concerns at the same time.Alike other methods secret sharing also have some limitations. To over come the shortcomings of secret sharing the notation of Verifiable secret sharing (VSS) is introduced. V SS is a two phase protocol (Sharing and Reconstruction) carried out among n players in the presence of an adversary who can corrupt up to t players. The goal of the V SS protocol is to share a secret S, among the n players during the sharing phase, such that in the reconstruction phase, the secret is reconstructed correctly. In this thesis we will discuss some known V SS protocols under the information theoretic setting over synchronous network, considering an active unbounded adversary. Weak secret sharing (W SS) is a variant of verifiable secret sharing, where the reconstructed value may also be some default value, in case the dealer is corrupted.In the present thesis we have proposed a 1-round W SS protocol having communication complexity of O(n). Previously, a 1-round W SS protocol with communication complexity of O(n ) was proposed. Thus, we get an improvement of θ(n) in the communication complexity.


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Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.


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