Subject: [MSEC] I need your help

From: "QinKe" <[email-masked]>
Date: Wed, 6 Apr 2005 21:46:29 +0800

Dear all:
I am a Chinese student who has strong interests in multicast. Now I have a thought about key management. When it comes to this thought, I have ever written to Prof Canetti and Thomas hardjono long ago. Maybe they are too busy to reply me. 
My thought is this: given that most of key managements need to send re-keying messages when someone join in or leave a group, I want to design such a mechanism that GC needn't send any re-keying messages when the membership has changed.
In detail, each legitimate member, for instance, member u_1 has his own key k_1, u_2 has k_2…u_n has his own key k_n, and GC has a series of keys denoted as kg_1,kg_2…kg_r. Each member sends his key to GC and then GC calculates K=f(k_1, k_2…k_n, kg_1, kg_2…kg_r). The sender uses K to encrypt messages need sending, denoted as C=E(K,M). After each legitimate member receives C, he can use his only key k_i to decrypt this ciphertext. When someone, for instance u_j will be kicked out, the GC only needs to calculate K'=f(k_1, k_2…k_(j-1), k_(j+1)…k_n, kg_1, kg_2…kg_r). Although the encryption key has changed from K to K', other members can also use their previous keys to decrypt ciphertext encrypted by K'.
I'd like to know whether there are similar schemes. If there are, would you please telling me where I can find such information? And if not, how can we realize this proposition? 
Thank you all in advance!
Best regards!

　　　　　　　　QinKe
　　　　　　　　[email-masked]
　　　　　　　　　　2005-04-06
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