Source : Computer & Security, Volume 22, No 5, 2003, pp. 453-456

Cryptanalyses and improvements of two cryptographic key assignment schemes for dynamic access control in a user hierarchy Source: Computer & Security, Volume 22, No 5, 2003, pp. 453-456 Author: Chien-Lung Hsu ,Tzong-Sun Wu Speaker: Yi-Fang Cheng Date: 2004 11/8

Outline • Introduction • Wu-Chang scheme • Shen-Chen scheme • Cryptanalyses • Improvement • Conclusion

C1 C2 C3 C4 C5 C6 Introduction (u11,u12,u13,u14) (u21,u22) (u31,u32,u33) (u41) (u61) (u51,u52)

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

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

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

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

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

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

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

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

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

Source : Computer & Security, Volume 22, No 5, 2003, pp. 453-456