Adrian Furtunǎ, PhD, CEH

(adif2k8@gmail.com)

DefCamp 2012

About me

PhD in information security, CEH

Penetration tester at KPMG Romania

Web apps

Infrastructure

Mobile apps

Source code reviews

+ some other annoying stuff

Always like to prove my point…

2

What is this all about?

3

The FUN part

What is this all about?

4

Our subject(s)

5

Our subject(s)

Digipass = security token

Disconnected, display, keypad

Used for:

User authentication (2nd factor) - OTP

Transaction signing (e.g. Internet Banking)

Vendors: Vasco, CryptoCard, RSA, etc

6

What is this all about? (still the fun part)

7

A machine that simulates human behavior when using a digipass

Brains • Command the machine

• Keep track of the logic

state

• Select the desired muscles

and send the necessary

signals

• Read an image from the

eyes

• Interpret the image and

make the next move

Neurons

• Transport the signal from

the brain to muscles

• Give the muscles the

necessary power/energy to

action

Muscles

• Push when powered on

• Release when powered

off

Eyes

• Provide images for

the brain

• Tell the brain what

is happening outside

OK… But why?

Motivation

8

The profit part

Remember the old rounding attacks against Internet Banking apps?

When working with two decimals most banks do the rounding to the closest value

8.3478 EUR ~= 8.35 EUR

8.3436 EUR ~= 8.34 EUR

max profit = 0.005 EUR

About rounding attacks:

“Assymetric Currency Rounding” by M'Raïhi, Naccache and Tunstall of Gemalto – 2001 - http://tinyurl.com/d5akdkk

“Is Your Online Bank Vulnerable To Currency Rounding Attacks?”, Mitja Kolsek of ACROSSecurity - 2012 – http://tinyurl.com/6wpg7ew

9

Rounding in currency exchange (1)

10

Use the Internet Banking application to transfer money between your own

accounts (e.g. RON -> EUR)

RON EUR EUR

(rounded)

Exchange rate

(RON / EUR rounded)

4.40 1 1.00 4.40 Official

2 0.4545 0.45 4.44

1 0.2272 0.23 4.34

0.5 0.1136 0.11 4.54

0.05 0.0113 0.01 5

0.03 0.0068 0.01 3

0.023 0.0052 0.01 2.3 The best

0.02 0.0045 0.00 not good

100 * (0.023 RON -> 0.01 EUR) => 2.3 RON = 1 EUR

Rounding in currency exchange (2)

11

The Bank said…

Known issue but we have the digipass to protects us:

1. User initiates currency exchange in IB application

2. Application sends challenge code to user

3. User inputs code into digipass

4. User reads digipass response

5. User sends the response to IB application

6. Application finalizes the transaction

12

The Bank said…

Known issue but we have the digipass to protects us:

1. User initiates currency exchange in IB application

2. Application sends challenge code to user

3. User inputs code into digipass

4. User reads digipass response

5. User sends the response to IB application

6. Application finalizes the transaction

13

Now automated!

We can make lots of transactions automatically

How much?

C1 = minimum amount of currency 1 (e.g. 0.023 RON)

C2 = minimum amount of currency 2 (e.g. 0.01 EUR)

Ex_b = exchange rate for buying C2 with microtransactions (e.g. 2.3). Ex_b = C1 / C2

Ex_s = exchange rate for selling C2 (e.g. 4.4) – real exchange rate – fixed by the Bank

Ex_b Ex_s

x RON y EUR z RON

14

z = y * Ex_s = (x / Ex_b) * Ex_s = x * (Ex_s / Ex_b)

multiplication rate = Ex_s / Ex_b

transactions required = x / C1

Currency 1 Multiplication

rate

Initial

amount (x)

Final

amount (y)

Gain Transactions

required

RON 4.4 / 2.3 = 1.9 100 RON 190 RON 90 RON ~ 20 EUR 100 / 0.023 = 4347

How the Banks should protect themselves

Limit the number of transactions that can be performed in a given time

Limit the minimum currency amount that can be exchanged in a transaction

Monitor for suspicious transactions (very small amounts)

State in the contract that such transactions are illegal

Introduce a small fee for currency exchange operations (e.g. 0.01 EUR)

15

Behind the curtains…

16

Back to the FUN part

External vs Internal instrumentation

Internal instrumentation (direct electrical connections):

Pros:

more reliable and faster

almost error free

Cons:

might not be always possible – some digipasses

deactivate if opened

must know the pinout of LCD screen (lots of pins!)

sensitive soldering required

mistakes can lead to deactivation

External instrumentation:

Pros:

No interference with digipass’s internals

Can be applied to any digipass model

Cons:

Pretty slow (but good for the “low and slow” approach)

Some (mechanics) errors occur on pressing buttons (resolvable by a more professional construction)

OCR process needs special (lightning) conditions to produce correct results

17

Electric diagram

18

D3 D2 D1 D0 Sx Digipass

key

0001 S1 0

0010 S2 1

0011 S3 2

0100 S4 3

0101 S5 4

0110 S6 5

0111 S7 6

1000 S8 7

1001 S9 8

1010 S10 9

1011 S11 =

1100 S12 S

1101 S13 ON/OFF

Optical Character Recognition

19

Original Cleared

background

Blurred Threshold applied OCR-ized

gocr / ocrad

7169309

-_16g309

1757450

1_5_G50

043i __ i_ì

OG3i _i_i

9a__641 4

9__6G1G

10 transactions / minute (6 seconds / transaction)

max 21600 transactions / day

enter PIN, type challenge code, read response image, do OCR

Our previous example:

100 RON 190 RON (gain ~20 EUR)

=> 4347 transactions * 6 sec/trans = 26082 sec = 7h:14m:42 s

Maximum amount to multiply per day:

21600 * 0.023 RON = 496.8 RON => final: 943.9 RON

gain 447 RON ~= 101 EUR/day

Money making machine?

Current performance

20

Photo gallery

21

The first POC

22

Development stages (1)

23

Development stages (2)

24

Development stages (3)

25

Development stages (4)

26

Final version - back

27

Final version - front

28

Demo

29

Thank you!

QUESTIONS ?

30

Adrian Furtunǎ, PhD, CEH

adif2k8@gmail.com

http://pentest-tools.com