Cryptosystems for hierarchical groups
This paper addresses the problem of information protection in hierarchical groups. Higher level groups of participants can control the information flow (the decryption ability) to lower level groups. If a higher level group decides to allow a lower level group to read the message, it passes a go ahead ticket so the lower level group can decrypt the cryptogram and read the message. The formal model of top-down hierarchical cryptosystems is given.
Two practical and efficient schemes are described. The first is based on the ElGamal system. The second applies the RSA system. In proposed schemes the dealer publishes a public key such that an individual can use it to send an encrypted message to the (hierarchical) group. Publication of both the group public key and the encryption method does not reveal the decision of the group. The proposed cryptosystems are immune against conspiracy attack.
The lack of verifiability of retrieved messages in threshold ElGamal cryptosystems is also discussed.
Unable to display preview. Download preview PDF.
- 1.T. Hwang C.M. Li and N.Y. Lee. Remark on the Threshold RSA Signature Scheme. In Advances in Cryptology — Proceedings of CRYPTO '93, Ed. D. Stinson, Lecture Notes in Computer Science, Vol. 773, pages 413–419. Springer-Verlag, 1993.Google Scholar
- 2.Y. Desmedt. Society and group oriented cryptography: A new concept. In Advances in Cryptology — Proceedings of CRYPTO '87, Ed. C. Pomerance, Lecture Notes in Computer Science, Vol. 293, pages 120–127. Springer-Verlag, 1988.Google Scholar
- 3.Y. Desmedt. Threshold Cryptosystems. In Advances in Cryptology — Proceedings of A USCRYPT '92, Eds. J. Seberry and Y. Zheng, Lecture Notes in Computer Science, Vol. 718, pages 3–14. Springer-Verlag, 1993.Google Scholar
- 4.Y. Desmedt and Y. Frankel. Threshold cryptosystems. In Advances in Cryptology — Proceedings of CRYPTO '89, Ed. G. Brassard, Lecture Notes in Computer Science, Vol. 435, pages 307–315. Springer-Verlag, 1990.Google Scholar
- 5.W. Diffie and M.E. Hellman. New Directions in Cryptography. IEEE Trans. on Inform. Theory, IT-22(6):644–654, November 1976.Google Scholar
- 6.T. ElGamal. A Public Key Cryptosystem and a Signature Scheme Based on Discrete Logarithms. IEEE Trans. on Inform. Theory, IT-31:469–472, 1985.Google Scholar
- 7.A. Shamir R.L. Rivest and L. Adleman. A Method for Obtaining Digital Signatures and Public-Key Cryptosystems. Communications of the ACM, 21(2):120–126, 1978.Google Scholar
- 8.A. Shamir. How to Share a Secret. Communications of the ACM, 22(11):612–613, November 1979.Google Scholar