Establishing authenticated channels and secure identifiers

in ad-hoc networks

Authors: B. Sieka and A. D. Kshemkalyani

(University of Illinois at Chicago)

Source: IJNS review paper

Reporter: Chun-Ta Li (李俊達 )

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Outline Introduction Problem statement Solution Analysis and Discussion Comments

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Introduction Motivation

Establishing a secure communication channels between nodes in a wireless ad-hoc network No trusted third party No requirement to share a prior context No out-of-band authentication channels

Proposing the use of secure identifiers use the hash of the public key for the identifier of a node

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Problem statement Given a set of nodes To establish an authenticated network (AN) For any given node j in the AN would satisfy the

following property

Node i possesses the corresponding private key Network layer functions are not available yet

radio broadcast in a wireless network

// All nodes in the AN know the authentic public keys of all other nodes in the AN //

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Solution

Notations Identity model

idi = hash(PKi) Message

MSG(contents) Type of message

JOIN, ACCEPT, UPDATE Public and private key

PKi and SKi

Digital signature SSK(M)

Radio broadcast

Sequence number copied from the last JOIN message from i (an integer) seqi

Local time when the most recent message from node idi was seen timei

Two columns of node j’s key table: the PK and seq column KeyTablej

The set of (PK,seq) entries from j’s key table KeyTableDeltaj

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Solution Outline of protocol to establish authenticated channels

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Solution 1. Send JOIN

A node i outside of an AN wants to join AN If it is a member of another AN

sub-networks merges

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Solution 2. Receive JOIN

First verify the validity of the digital signature computes idi = hash(PKi) and check if there exists an

entry with idi for node i in j’s key table (a) idi entry does not exist new entry should be added to

key table broadcast ACCEPT and UPDATE message (b) idi entry does exist (idi = idk)

i. PKi ≠ PKk and seqi < seqk discard JOIN message

ii. PKi = PKk and seqi < seqk discard JOIN message

iii. PKi = PKk and seqi > seqk seqk should be updated to seqi

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Solution 3. Send ACCEPT

A node i that is not a member of AN without an identifier conflict Node j broadcast the ACCEPT message

4. Receive ACCEPT (ANjoin+accept) check the signature of the message add entries from the KeyTable field of the ACCEPT mess

age to its key table broadcast an UPDATE message

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Solution 5. Send UPDATE

A node that is a member of the ANjoin or ANaccept

New entries are added to the key table in the following cases

The KeyTableDelta field of the message should contain all the (PK,seq) pairs

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Solution 6. Receive UPDATE

A node that is a member of ANjoin or ANaccept

check the signature of the message add entries from the KeyTableDelta field to its key table execute step 5

7. Key Timeout Every node should maintain a timestamp associated with every

entry in its key table An entry should be deleted from the key table if the timestamp

is order than a specified threshold value

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Analysis and Discussion Security analysis

Against impersonation attacks Digital signature and a node’s identity is bound to its

public key

Against replay attacks Use of sequence number

Sybil attack threat (an entity from generating multiple

public, private key-pairs and multiple identities) Reputation management approaches

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Analysis and Discussion Complexity analysis

// N be the number of entries in the sender’s key table

// M be the number of fresh entries in the sender’s key table

• Overall Bootstrapping Cost – Broadcasts

O(n2) // n be |AN| after JOIN operations

• Overall Bootstrapping Cost – Message Space

O(|AN|2)

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Comments The solution for establishing authenticated

channels in ad-hoc network is simple There are no notable problems found in this

paper Descriptions of Table 2 4 typos

Evaluation of Paper: Confirmatory

Recommendation: Accept after minor revision