1. Cryptanalyses and improvements of two cryptographic key assignment schemes for dynamic access control in a user hierarchy
Source: Computer & Security, Vol22, No 5, pp ,2003
Author: Chien-Lung Hsu ,Tzong-Sun Wu
Speaker: Yi-Fang Cheng
Date: /8

2. Outline Introduction Wu-Chang scheme Shen-Chen scheme Cryptanalyses
Improvement
Conclusion

3. Introduction C1 C2 C3 C5 C4 C6 (u11,u12,u13,u14) (u21,u22)

4. Wu-Chang scheme (1/2)
Key generation stage : C1 C2 C3 C5 C4 C6

5. Wu-Chang scheme (2/2)
Key derivation stage : C1 C2 C3 C5 C4 C6
u31
u52

6. Shen-Chen scheme (1/2)
Key generation stage : C1 C2 C3 C5 C4 C6

7. Shen-Chen scheme (2/2)
Key derivation stage : C1 C2 C3 C5 C4 C6

8. Cryptanalysis of Wu-Chang scheme
C3 can get the private key of C4 C1 C2 C3 C5 C4 C6

9. Cryptanalysis of Shen-Chen scheme
C3 can get the private key of C4 C1 C2 C3 C5 C4 C6

10. Improvement of Wu-Chang scheme
Modify the polynomial function by using a one-way hash function

11. Improvement of Shen-Chen scheme
Modify the polynomial function by using a one-way hash function

12. Conclusion
To eliminate the security leaks by using a one way hash function