Efficient Multi-level Threshold Attribute Based Encryption

Anonymous access control is a very desirable property in various applications e.g. encrypted storage in distributed environments; and attribute based encryption (ABE) is a cryptographic scheme that is targeted to achieve this property. ABE is an encryption mechanism that is useful in settings where the list of users may not be known apriori, but all users may possess certain credentials which can be used in determining access control and at the same time providing a reasonable degree of anonymity. Ciphertext policy attribute based encryption is a scheme that gives a natural way to link the access policy with the ciphertext, and attributes with the keys; and cleverly combine them at a later stage to provide secure access to protected data. In most ABE schemes the size of the ciphertext is quite large and is of the order of the number of attributes. In this work we present our approach for a multi-level threshold attribute based encryption scheme whose ciphertext size depends only on the size of the policy and is independent of the number of attributes.