1. 1. S. G. Akl and P. D. Taylor, ―Cryptographic Solution to a Problem of Access Control in a Hierarchy,‖ ACM Transactions on Computer Systems (TOCS), vol. 1, no. 3, pp. 239–248, 1983. 
   2. G. C. Chick and S. E. Tavares, ―Flexible Access Control with Master Keys,‖ in Proceedings of Advances in Cryptology – CRYPTO ’89, ser. LNCS, vol. 435. Springer, 1989, pp. 316–322.
   3. W.-G. Tzeng, ―A Time-Bound Cryptographic Key Assignment Scheme for Access Control in a Hierarchy,‖ IEEE Transactions on Knowledge and Data Engineering (TKDE), vol. 14, no. 1, pp. 182–188, 2002.
   4. G. Ateniese, A. D. Santis, A. L. Ferrara, and B. Masucci, ―Provably-Secure Time-Bound Hierarchical Key Assignment Schemes,‖ J. Cryptology, vol. 25, no. 2, pp. 243–270, 2012.
   5. J. Benaloh, M. Chase, E. Horvitz, and K. Lauter, ―Patient Controlled Encryption: Ensuring Privacy of Electronic Medical Records,‖ in Proceedings of ACM Workshop on Cloud Computing Security (CCSW ’09). ACM, 2009, pp. 103–114
   6. R. Canetti and S. Hohenberger, “Chosen-Ciphertext Secure Proxy Re-Encryption,” in Proceedings of the 14th ACM Conference on Computer and Communications Security (CCS ‟07). ACM, 2007, pp. 185–194.
   7. L. Hardesty, “Secure computers aren‟t so secure,” MIT press, 2009, http:// www. physorg. com/news 176107396.html.
   8. C. Wang, S. S. M. Chow, Q. Wang, K. Ren, and W. Lou, “Privacy-Preserving Public Auditing for Secure Cloud Storage,” IEEE Trans. Computers, vol. 62, no. 2, pp. 362–375, 2013.
   9. B. Wang, S. S. M. Chow, M. Li, and H. Li, “Storing Shared Data on the Cloud via Security-Mediator,” in International Conference on Distributed Computing Systems - ICDCS 2013. IEEE, 2013
   10. G. C. Chick and S. E. Tavares, “Flexible Access Control with Master Keys,” in Proceedings of Advances in Cryptology – CRYPTO ‟89, ser. LNCS, vol. 435. Springer, 1989, pp. 316–322.
   11. W.-G. Tzeng, “A Time-Bound Cryptographic Key Assignment Scheme for Access Control in a Hierarchy,” IEEE Transactions on Knowledge and Data Engineering (TKDE), vol. 14, no. 1, pp. 182–188, 2002.