A time-bound hierarchical key assignment cryptosystem with no lifetime limit

Key assignment schemes for controlling access in a partially ordered hierarchy has been studied for years. Recently, the research of this topic has focused on assigning hierarchical keys which are also sensitive to time. Most of the proposed time-bound hierarchical key assignment schemes in the literature are extremely difficult to extend the life of a system since it may require to re-assign existing keys. Changing existing keys leads to a very time-consuming process: data reencryption. By the author's best knowledge, this issue was not yet studied in the literature. In this paper, a new scheme is proposed, in which the system's life can be extended without affecting any existing key so that no data re-encryption is necessary.