# Presentation: 174883

##  Toward Mitigating Denial of Service Attacks inPower-Constrained Sensor Networks

- Ortal Arazi, Hairong Qi
- College of Engineering
- Dept. of Electrical & Computer Engineering
- The University of Tennessee
- Cyberspace Sciences & Information Intelligence Research Group (CSIIR)
- Oak Ridge National Laboratory, Oak Ridge

## Instigating  Communication 

- Instigating  Communication

- Insecure channel

- Bob

- Alice

**Alice and Bob: legitimate users**
**They would like to start communicating**** **

- key?
- “talk”?

- Lets “talk”

## Denial of Service Mitigation

- Insecure channel

- Bob

- Trudy

**Trudy wants to:  **** ****1) Drain Bob’s energy**
**	****	****       ****2) Impede him from talking to **
**                        ****other legitimate users **
**	****   ****How can we prevent that? **

## Denial of Service Mitigation Procedure

- Alice

- Bob

- Part A:

- Alice proving to Bob her validity

- A relatively energy draining procedure on Trudy’s side

- If Proved

- Part B:

- Bob proving to Alice his validity

- A relatively non energy draining procedure on Bob’s

- side

- If the authentication is

- successful, as a result

- Alice and Bob will also

- have a shared key

## The Denial of Service Mitigation 

- Part A

-     (nA, e)→ Alice’s public key
-     (nA, dA)→ Alice’s private key
-     CRA → Alice’s certificate
-     IDA → Alice’s identification

- CR- A certificate
- The CA’s signature on the association between nA and IDA

## The Denial of Service Mitigation 

- Part A (cont)

## Timing and energy considerations 

- (Part A)

- ~ 160 mJ
- ~250 msec
- (for a 512 bit key)
- All other energy and time
- consumptions (from the
- other procedures)
- are _negligible_

## Calculating the keys

- Pi- Pseudo random prime number

-    ( nA,e)→ Alice’s public key
-    (nA,dA)→ Alice’s private key

- Euler’s Totient Function            returns the number of Integers less
- than nA

## Checking the Certificate 

- nCA and dCA are calculated using the exact procedure
- indicated above

## The Denial of Service Mitigation Procedure

## The Denial of Service Mitigation 

- Part B

- How can Bob prove his validity?
- Several solutions:
- Using the self-certified fixed key method
- Using RSA
- Using ECDSA

- I am Bob!

- ??

## The Denial of Service Mitigation 

- Part B

**(1) Using the self-certified fixed key method**

- When calculating the self-certified fixed key, Bob is authenticated!
- Both have the message m Bob sent in part A

- xA[H(IDB , UB)* UB + R ]  ,

- xB[H(IDA , UA)* UA + R ]

- The final ephemeral key:
- f( fixed key, m/without the Y LSB sent on the open channel)

- t

- Y LSB of m

## Self certified DH key generation: Fixed key

- Node i

- Node j

- IDj , Uj

- IDi , Ui

- IDv: identification of node v                                     - scalar
- Uv    : node v’s public key, generated by the CA          - a point on the curve
- Xv   : node v’s private key, generated by the CA         - scalar

- Each node is given by the CA (Certifying authority) a set of public and private keys:
- (Uv, Xv)

- Node i calculates: xi[H(IDj , Uj),* Uj + R ]        =

- xj[H(IDi , Ui),* Ui + R ]  :Node j calculates

## Self certified DH key generation: Fixed key

- R    : the CA’s public key  = d*G                                           - a point on the curve
- d    : the CA’s private key                                                    - scalar
- G    : a generating group-point, used by all relevant nodes   - a point on the curve
- hv    : a random 160 bit number generated by the CA           - scalar

- Node i calculates:
- xi[H(IDj , Uj),* Uj + R ]
- =xi[H(IDj , Uj),* hj * G  + d*G ]
- =xi[H(IDj , Uj),* hj + d] *G
- =     xi* xj *G

-  mathematical assertions ...
- As given by the CA:
- Ui= hi * G                                                        Uj= hj * G
- xi= [H(IDi, Ui),* hi + d ] mod org G                xj= [H(IDj, Uj),* hj + d ] mod org G

- Node j calculates:
- xj[H(IDi, Ui),* Ui + R ]
- =xi[H(IDi, Ui),* hi * G  + d*G ]
- =xi[H(IDi , Ui),* hi + d] *G
- =      xj* xi *G

## The Denial of Service Mitigation 

- Part B

**(2) Using RSA**

- If so, the final ephemeral key:   **Z**

- Bob calculates:
- Bob send Alice:
- Alice calculates:

- CRB
- IDB
- nB
- SB

## The Denial of Service Mitigation 

- Part B

**(3) Using ECDSA**

- If so, the final ephemeral key:   **Z**

- Bob:
- Generates a random number: u. Calculate                  .             C- the scalar representation of point V.
- Calculates                                            .                                                  The signature is the pair (C,L)
- Sends Alice  (C,L)
- Alice:
-   Computes:
- Obtains the curve point:                                                           C’- the scalar representation of point P
- If C=C’, then the signature is valid, it is Bob!

## The Denial of Service Mitigation, Part B

- Comparing the three methods

|  | Method 1
(Fixed key) | Method 2
(RSA) | Method 3
(ECDSA) |
| --- | --- | --- | --- |
| Part A
Alice proving her identity | Alice: 6

Bob: ~0
 | Alice: 6

Bob: ~0
 | Alice: 6

Bob: ~0
 |
| Part B
Bob proving his identity | Alice: 2 
Bob: 2 | Alice: ~0 
Bob: 6 | Alice: 2 
Bob: 1
 |
| Overall computational overhead | ~10  | ~12 | ~9 |

- The time is measured in: ECC point by scalar multiplications
- Approximately: 40 msec

## Conclusions

- PKC implementation in WSN is feasible
- ECC shows promise as crypto technology
- DoS is a primary threat
- Introduced a hybrid RSA/ECC framework for mitigating DoS attacks
- Using the fixed key approach or the ECDSA approach proved to be highly beneficial

-   Thank You
-   Questions ?