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SET ID: 03SETMSW0819

A NOVEL HUFFMAN TREE SCHEME FOR

GROUP REKEYING

D.Ramya , A.Anitha, P.Lakshmi

Abstract:

Muliticast is a one-to-many or many-to-many communication mode for

special group members, group communication is basis for many

multimedia and web application. The group management is a criticalproblem in a large dynamic group. All group keying protocols incur

communication and computation at the group key controller and at the

group member.

Introduction:

Multiplexing is a techniques for communicating mode for a group

members. Multicasting techniques are based on the Logical Key

Rekeying (LKH) scheme. The group members proposes organizing the

LKH trees by the key management and the key by the path from the root,

all the leaf is corresponding to a members. The root of the tree is

respected of group key. This management is controlled by the group

controller.

The biggest challenge in multicast security is to maintain a group key that

is shared by all the group members. The key can be used to provide secrecy

and integrity protection for the communication.

The cost of compromise recovery operation in LKH is proportional to

the depth of the LKH tree. It proposes maintaining a balanced tree and it

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gives a uniform cost of 0(log n) rekeys for n-member group. Similarly,

Huffman key tree can be adjusted adaptively with the frequency of users

joining in or leaving from multicast group. Our analysis proves that the

scheme can provide the security of multicast rekeying, as well as can ensure

that the average cost of rekeying is least even when adjusting

Huffman key tree dynamically.

We restrict our attention to algorithms which do not require changing the

location of the existing members.

The main structural decision for the tree organization is where to put a

new members at insertion time. The insertion operation should observe the

current locations of existing members.

Root Root

Y Put(M,X) Y

X N

M X

The node m is insert in to the group and n is a internal node, inserted in

the tree. The member m is inserted in the group and a new internal node

n id inserted in the tree, m is linked underneath. The new member m,

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we written as Put (m,x) at a given location for insertion operation. The

traditional LKH, trees each node x has a probability field x.p which is

cumulative probability of the members in the subtree rooted at x (similar to

as it is in Huffman tress), i.e., x.p is equal to x.left.p+x.right.p if x is an

internal node. The Put procedure shown above should also update the p

field of all nodes affected by the insertion, as well as setting up the

appropriate links for m and n.

The principle of insert1 is to insert a new node in a way which obtains the

best partitioning at every level so the resulting tree will have an AEPL closeto the optimal bound of the sum(p_i*-log(p_i)).

K_r

K_0 K_1

K_OO K_01 K_10 K_11

K_000 K_001 K_010K_011 K_100 K_101 K_110 K111M_1 M_2 M_3 M_4 M_5 M_6 M_7 M_8

In this figure ,member M_1 holds a copy of the keys

K_000,K_00,K_0, and K_r; member M_2 holds a copy of

K_001,K_00,K_0, and K_r; and so on.

In case of a compromise, the compromised keys are

changed

and the new keys are multicast to the group encrypted by

their children

keys. For ex. Assume the keys of M_2 are compromised. First

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K_001 is

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changed and sent to M_2 over a secure unicast channel. Then K_00 is

changed, two copies of new key are encrypted by K_000 and

K_001, and sent to the group. Then K_0 is changed and sentto the group, encrypted by K_0 and K_1.

From each encrypted message, the new keys are

extracted by the group members who have a valid copy of

one of the(child)

encryption keys.

If the security policy requires backward and forward

secrecy for group communication (i.e., a new member

should not be able to encrypt the communication that took

place before its joining and a

former member should not be able to decrypt the

communication that takes place after its leaving ) then the

keys on the leaving /joining

members path in the tree should be changed in a way .

similar, to that describe above for compromise recovery.

Result:

We showed the methods which improve the rekey message

complexity cost of the LKH tree for multicast key management bt

probabilistic organization of the LKH tree. Besides LKH scheme of

Wallner.