ABSTRACT
This chapter presents attribute-based encryption. It is a type of public-key encryption in which the secret key of a user and a ciphertext are dependent upon the attributes of the user. This scheme involves two additional components: access tree, and set of attributes. When multiple parties need same data, that may contain sensitive information including personal, financial, or medical details. It requires some additional measures to hide specific details of the user, compared to conventional public key cryptography, where private key is different for each user. The access structure can be seen as the threshold function, that is, at least k number of parties must use their share to construct the secret. Furthermore access structure can be represented as a tree such that there is a threshold function associated with each node of the tree. A user will be able to decrypt a ciphertext, if and only if his attributes satisfy the access structure associated with ciphertext.
