An attribute based encryption scheme (ABE) is a cryptographic primitive in which every user is identified by a set of attributes, and some function of these attributes is used to determine the ability to decrypt each ciphertext. Chase proposed the first multi authority ABE scheme in TCC 2007 as an answer to an open problem presented by Sahai and Waters in EUROCRYPT 2005. However, her scheme nee...

Secret image sharing (SIS) technique protects an image by sharing it among many users. Most existing SIS schemes produce meaningless shadow images, which tends to cause attackers’ suspicion. In this paper, a meaningful secret image sharing scheme is proposed that, for the first time, uses mosaic images as the shadow images. The secret image is divided into several parts, and each part is transf...

In the second chapter, the notion of a social secret sharing (SSS ) scheme is introduced in which shares are allocated based on a player’s reputation and the way she interacts with other parties. In other words, this scheme renews shares at each cycle without changing the secret, and it allows the trusted parties to gain more authority. Our motivation is that, in real-world applications, compon...