1 A secure broadcasting cryptosystem and its application to grid computing Eun-Jun Yoon, Kee-Young Yoo Future Generation Computer Systems (2010),doi: /j.future Received date: 25 February 2010 Revised date: 13 September 2010 Accepted date: 24 September /10/14 廖俊威

2 Broadcasting Cryptosystem The main purpose of a broadcasting cryptosystem is to –establish a secure communication channel from a sender to a group of legal receivers. In the broadcasting cryptosystem, –a sender can broadcast an encrypted message to a group of legal receivers. –Then, only legal receivers can decrypt the message, –and illegal receivers cannot acquire any important information from the broadcast message.

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4 The disadvantages of previous researches: –Need many broadcasting messages for a group of legal receivers. –Hard to add new users into the previous constructed groups Liaw [21] proposed a secure broadcasting cryptosystem with fewer broadcasting messages based on the RSA cryptosystem and symmetric cryptosystem, which allows easy addition of new users into the active groups. Sun [22] showed that Liaw’s broadcasting cryptosystem becomes actually infeasible since a prohibitively large amount of information must be kept by each user, and be sent as the rekey message for each broadcast. Tseng and Jan [23] also pointed out the several security weaknesses in the Liaw’s cryptosystem in To remedy this attack, Tseng and Jan also proposed a modification broadcasting cryptosystem. in 2006, Masque and Peinado [24] pointed out that Tseng and Jan’s broadcasting cryptosystem [23] actually does not work due to incorrect arithmetic and then presented a redefined Liaw’s broadcasting cryptosystem, in 2008, Zhu-Wu [29] showed that the redefined Liaw’s scheme [24] is still insecure in that an unauthorized user is able to obtain the shared secret, which is only intended for certain privileged users. Zhu-Wu did not provide an improvement. This paper found that the redefined Liaw’s broadcasting cryptosystem has another security problems, and proposed a new secure authenticated broadcasting cryptosystem.

5 The redefined Liaw’s broadcasting cryptosystem System setup phase

6 Broadcasting phase a sender S = U 1 wants to broadcast a message M to a group of users G = {U i } a i =2

7 Decryption phase Zhu-Wu’s cryptanalysis: unauthorized user U j can get sk

8 Future cryptanalysis 1.Integrity violence of the session key from illegal modification

9 2.Session key modification attack

10 3.Message modification attack This message modification attack can be succeed by the attacker because the legitimate receivers do not verify the integrity of the decrypted message.

11 Proposed authenticated broadcasting cryptosystem System setup phase

12 Broadcasting phase a sender S = U 1 wants to broadcast a message M to a group of users G = {U i } a i =2

13 Decryption phase

14 Application to grid computing environments

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16 Conclusions This research presents a new secure broadcasting cryptosystem. It is suitable for grid computing environments. It provides strong security compared with related cryptosystems. It provides secure authentication and secure session key establishment.