Subject: [MSEC] Algorithm and implementation of Diffie-Hellman

From: Yan Li <[email-masked]>
Date: Mon, 08 Dec 2003 21:37:50 -0600

Hi, there,

I hope to compute n-party group keys with DH within one group. Is there an 
algorithm to implement it?

Thanks for any help!

Regards,

Yan Li

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From: Mark Baugher <[email-masked]>
Date: Tue, 09 Dec 2003 08:08:28 -0800

hi
   Have you looked at Cliques?

Mark

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From: Scott Fluhrer <[email-masked]>
Date: Tue, 09 Dec 2003 08:54:02 -0800

>algorithm to implement it?

What security properties are you hoping to achieve?

-- 
scott

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From: Sead Muftic <[email-masked]>
Date: Tue, 09 Dec 2003 12:25:16 -0500

>algorithm to implement it?

Depends what you want to do: either to use DH bilaterally between each group
member and GSAKMP controller to securely DISTRIBUTE group key to each 
individual
group member or to use extended DH protocol to ESTABLISH group key within
a group.

In the former case, you may use DH implementation in JCE, for the later 
case I guess the best
protocol is by I. Ingemarsson, but I don't know of any implementation, so 
that would be your
R&D exercise.

Since we have the implementation of the full GSAKMP protocol, supporting 
secure instant messaging
and secure forum, but not using DH (in fact we use SSL between group 
members and GSA Controller)
if you will do any of the above in Java, we would be glad to integrate your 
results in our system and
later swap them.

Regards,

Sead Muftic
CSPRI/GWU

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From: Yongdae Kim <[email-masked]>
Date: Tue, 09 Dec 2003 15:23:58 -0600

Yan,

Currently Cliques, TGDH, STR, and BD are implemented and available from 
http://sconce.ics.uci.edu/cliques/download.html ... Communication is 
supported by Spread group communication system and integrated version is 
available from http://cnds.jhu.edu/research/group/secure_spread/.

Cheers,
Yongdae

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From: Yan Li <[email-masked]>
Date: Wed, 10 Dec 2003 15:17:36 -0600

Thanks for all your response.

I developed an application to provide P2P synchronous services to groups. 
These services include group and private text chat, this application is a 
Java application that uses the JXTA P2P framework to provide these services.

I am planning to encrypt the group message with a symmetric algorithm, such 
as RC4 or DES, and multicast the encrypted message to the members within 
one group. I hope to establish a group key for the group communication. No 
authentication will be considered in this case. To be more precise, the 
communication model assumes all peers authenticated in advance to work in a 
trusting environment but the communication to be not private. The trusted 
peers cannot be involved in unauthorized activities such as eavesdropping 
and MIME. The attacks are assumed to be active and passive, i.e. the 
attacker may eavesdrop on arbitrary communication and interfere it. The 
group size is assumed to scale up to hundreds of peers.

Now my problem is how to establish a group key? How to select the big 
random number, exponentiation and the large prime for DH? How can 
I  generate the key for RC4 or DES?  The requirement for my application is: 
simple, secure, efficient and practical. I know Cliques and GSAKMP are good 
for secure multicast group management, but they are too complex to be 
implemented and need high computation cost.

regards,

Yan

At 03:23 PM 12/9/2003 -0600, you wrote:
>>>I hope to compute n-party group keys with DH within one group. Is there 
>>>an algorithm to implement it?
>>

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From: [email-masked]
Date: Tue, 9 Dec 2003 14:29:29 -0500

There is a Tree-based Group Diffie Hellman (TGDH) that has been shown to be
scalable to groups of 50 nodes. I am not aware of any standardization effort
on this. Please refer to the following paper.

An Efficient Tree-based Group Key Agreement using Bilinear Map 
by Sangwon Lee, Yongdae Kim, Kwangjo Kim, and Dae-Hyun Ryu.

Subrata

> What security properties are you hoping to achieve?

Subrata Goswami, Ph.D.