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SAODV

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Title: SAODV

1
SAODV

2
Introduction

3
Security Requirements

Import authorization Route information will be
imported only if it concerns to the node that is
sending the information.
Source authentication To be able to verify that
the node is the one it claims to be.
Integrity To be able to verify the received
routing information has not been altered.
Data authentication The combination of the two
last ones.

4
Security Attacks in AODV (1/2)

Impersonate a node S by forging a RREQ with its
address as a originator address.
When forwarding a RREQ generated by S to discover
a route to D, reduce the hop count field to
increase the chances of being in the route path
between S and D, so it can analyze the
communication between them. A variant of this is
to increment the destination sequence number to
make the other nodes believe that this is a
'fresher' route.
Impersonate a node D by forging a RREP with its
address as a destination address.
A malicious node M impersonate a node by forging
a RREP that claims that the node is the
destination and, to increase the impact of the
attack, claims to be a network leader of the
subnet SN with a big sequence number and send it
to its neighbors. In this way it will became (at
least locally) a blackhole for the whole subnet
SN.

5
Security Attacks in AODV (2/2)

Selectively, do not forward certain RREQs and
RREPs, do not reply certain RREPs Or, and do not
forward certain data messages. This kind of
attack is specially hard to even detect because
transmission errors have the same effect.
A malicious node M forges a RERR message
pretending it is the node S and sends it to its
neighbor D. The RERR message has a very high
destination sequence number dsn for one of the
unreachable destinations (U). This might cause D
to update the destination sequence number
corresponding to U with the value dsn and,
therefore, future route discoveries performed by
D to obtain a route to U will fail (because U's
destination sequence number will be much smaller
than the one stored in D's routing table.
Generating a RREP with a maximum destination
sequence number.
And many more.

6
SAODV Digital Signatures

Digital signatures are used to protect the
non-mutable data in the RREQ and RREP messages.
(Solves attacks 1 3)
Problem Replies generated by intermediate nodes.
Solutions
They don't
Double Signature Extension Messages

7
SAODV Hash Chains

Hash chains are used in SAODV to authenticate the
hop count of the AODV routing messages (not only
by the end points, but by any node that receives
one of those messages). This solves the attack
2. A hash chain is formed by applying a one way
hash function repeatedly.
Every time a node wants to send a RREQ or a RREP
it generates a random number (seed). Sets
Max_Hop_Count to the TimeToLive value in the IP
header, and Hash to the seed value. Then, it
calculates Top_Hash by hashing seed Max_Hop_Count
times.
Hash seed Top_Hash hMax_Hop_Count(seed)
Every time a node receives a RREQ or a RREP it
verifies the hop count of the message. Before
rebroadcasting a RREQ or forwarding a RREP, a
node hashes one time the Hash value in the
Signature Extension.
Top_Hash hMax_Hop_Count Hop_Count(seed) Hash
h(Hash)

8
What about RERR messages?

They have a huge amount of mutable information.
It is not relevant if it is a generated or
forwarded RERR.
A node sending a RERR signs the whole message and
nodes receiving verify the signature.
Nodes do not update dsn from a RERR (solves
attack 6).

9
Rebooting and Sequence Numbers

Nobody tells me what is my dsn (solves attack
7).
If I have memory I will remember my dsn after
rebooting. Otherwise I wait.
No cyclic sequence numbers. And once I have
reached the maximum seq num, I should probably
get new key pair (to avoid reply attacks).

10
Analysis

Hop count authentication by using hash chains is
not perfect A malign node might forward a
message without increase the hop count.
More secure approaches are too expensive, and
they don't solve tunneling attacks.
Tunneling attacks are not solved by SAODV. But,
who can solve them?
Theoretically, misbehaving detection schemes. But
not in practice.

11
Misbehaving Detection Obscurity

It is hard to distinguish misbehaving from
transmition failures and other events.
It has no real means to guarantee the integrity
and authentication of the routing messages!

Obscurity is not the way to obtain security.
There is no such thing as a tampering resistant
device.
We want open standards.

12
Future Work

Try to reduce the processing power requirements
of SAODV due to the use of asymmetric
cryptography.
Add SAODV extension to the NRC-AODV
implementation (done by me). NRC-AODV has all the
basic AODV features, and was tested in the first
AODV interoperability test. (NRC stands for Nokia
Research Center)

13
Thanks To

N. Asokan He has contributed to the saodv draft
with several improvements and corrections. He
suggested the use of hash chains to authenticate
the hop count and, that intermediate nodes should
sign the lifetime of the RREPs.
Everybody who has been discussing SAODV with me
or Asokan.
To you For your attention.

14
More Info