Hacker Chronicles 2 (Alt)/The_Hacker_Chronicles_Volume_II-CD2.iso/misc/atm.txt

Text File | 1995-01-03 | 21.5 KB | 892 lines

(>View: automatic teller machines
From ames!amdahl!nsc!voder!wlbr!gins Mon Jul 13 12:41:23 PDT

Article 479 of sci.crypt:

Path: ames!amdahl!nsc!voder!wlbr!gins

>From: [e-mail] (Fred Ginsburg)

Newsgroups: sci.crypt

Subject: Re: ATM secret codes

Summary: ATM stuff

 LONG...

Message-ID: <[e-mail]>


Organization: Eaton IMS, Westlake Village, CA

Lines: 445



A

In article <[e-mail]>, [e-mail] (Vu Qui Hao-Nhien) writes:

> In article <[e-mail]> [e-mail] (Karl Denninger) writes:

> >In article <[e-mail]>, [e-mail] (Karl Lehenbauer) writes:

>

> The transactions done by ATM sometimes (not always) are kept by the

> machine until remove by human hands and fed to the bank's computer at

> its headquarters.  Hence not much communication between ATM and the

> outside world.

> --

on computer security.  Any questions, give a call (818-706-4146)



or send to {trwrb,ihnp4}!wlbr!gins





***************  Track Layouts ************************



This is off the top of my head, but is 99% there.  Also I'll ignore

some obsolete stuff.



The physical layout of the cards are standard.  The LOGICAL makeup

varies from institution to institution.  There are some generally

followed layouts, but not mandatory.



There are actually up to three tracks on a card.



Track 1 was designed for airline use.  It contains your name and

usually your account number.  This is the track that is used when

the ATM greets you by name.  There are some glitches in how things

are ordered so occasionally you do get "Greetings Bill Smith Dr."

but such is life.  This track is also used with the new airline

auto check in (PSA, American, etc)



Track 3 is the "OFF-LINE" ATM track.  It contains suc@e603ty

information as your daily limit, limit left, last access, account

number, and expiration date.  (And usually anything I describe in track

2).  The ATM itself could have the ability to rewrite this track to

update information.



Track 2 is the main operational track for online use.  The first thing

on track to is the PRIMARY ACCOUNT NUMBER (PAN).  This is pretty

standard for all cards, though no guarantee.  Some additional info

might be on the card such as expiration date.  One interesting item

is the PIN offset.   When an ATM verifies a PIN locally, it usually

uses an encryption scheme involving the PAN and a secret KEY.

This gives you a "NATURAL PIN" (i.e. when they mail you your pin, this

is how it got generated.)  If you want to select your own PIN, they

would put the PIN OFFSET in the clear on the card.  Just do modulo 10

arithmetic on the Natural PIN plus the offset, and you have the

selected PIN.  YOUR PIN IS NEVER IN THE CLEAR ON YOUR CARD.  Knowing

the PIN OFFSET will not give you the PIN.  This will required the

SECRET KEY.



Hope that answers your question









************ Deposits at ATMs ************************



Deposits on ATM:



Various banks have various systems.  As an example, at CITIbank

a deposit was made to a specific account.  Your account was updated

with a MEMO update, i.e. it would show up on your balance.  However

it did not become AVAILABLE funds until it was verified by a teller.

On the envelope was Customer ID number, the envelope number and

the Entered dollar amount, the branch # and the Machine #.



There was also a selection for OTHER PAYMENTS.  This allowed you to

dump any deposit into the ATM.



What are you assured then when you deposit to an ATM ?



1) You have a banking RECORD (not a reciept at Citibank).  If you

   have this record, there is a VERY high percentage that you

   deposited something at that ATM.



2) Some banks have ways of crediting your deposit RIGHT NOW.

   This could be done by a balance in another account (i.e. a long

   term C.D. or a line of credit.)  That way they can get you if

   you lied.





**************  ATM Splitting a Card in half ***************



   I've worked with about 75% of the types of machines on the market

and NONE of them split a card in half upon swallow.  However, some

NETWORKS have a policy of  slicing a card to avoid security

problems.



Trusting an ATM.

Intresting you should bring this up, I'm just brusing up a paper

describing a REAL situation where your card and PIN are in the clear.

This involves a customer using a bank that is part of a network.

All the information was available to folks in DP, if they put in some

efforts to get it.











          Mis-Implementation of an ATM PIN security system





1.  Synopsis

In an EFT (Electronic Funds Transfer) network, a single node which  does

not  implement  the  proper  security  can  have  effects throughout the

network.  In this paper, the author describes an example of how security

features  were  ignored, never-implemented, and/or incorrectly designed.

The human factors involved in the final implementation are  explored  by

showing  several major vulnerabilites caused by a Savings and Loan and a

regional EFT network's lack of vigilance in installing  an  EFT  network

node.   While  using  an  EFT  system as an example, the concepts can be

extrapolated into the implementation of other secured systems.





2.  Background

A small Savings and Loan  was  setting  up  a  small  (10  to  16  ATMs)

proprietary  Automatic  Teller  Machine (ATM) network.  This network was

then intended to link up to a regional network.  The manufacturer of the

institution's  online  banking  processor  sent an on-site programmer to

develop the required interfaces.



An ATM network consists of three main  parts.   The  first  is  the  ATM

itself.   An ATM can have a range of intelligence.  In this case the ATM

was able to decode a  PIN  (Personal  Identification  Number)  using  an

institution  supplied  DES  (Data Encryption Standard) key.  It was then

required to send a request for funds to the host where it would receive

authorization.



The second portion of the network is the ATM controller.  The controller

monitors the transaction, and routes the message  to  the  authorization

processor.   The  controller  would  also generally monitor the physical

devices and statuses of the ATM.



The third portion of the network is the authorization system.   In  this

case  customers  of  the  local  institution  would have the transaction

authorized on the same processor.  Customers  from  foreign  (i.e.   one

that  does not belong to the institution that runs the ATM) institutions

would be authorized by the regional  network.   Authorization  could  be

from  a  run-up  file which maintains establishes a limit on withdrawals

for a  given  account  during  a  given  period.   A  better  method  is

authorization direct from the institution which issued the card.





3.  Security

The system has a two component key system to allow access to the network

by the customer.  The first  is  the  physical  ATM  card  which  has  a

magnetic stripe.  The magnetic stripe contains account information.  The

second component is the Personal Identification Number (PIN).   The  PIN

is hand entered by the customer into the ATM at transaction time.  Given

these  two  parts,  the  network  will  assume  that  the  user  is  the

appropriate customer and allow the transaction to proceed.



The Magnetic stripe is in the clear and may be assume to be reproducible

using various methods, thus the PIN is crucial security.







Security

PIN security





3.1.  PIN security





3.1.1.  PIN key validation method



PINs can be linked up to a particular card in a  number  of  ways.   One

method  puts  the  PIN  into  a central data base in a one-way encrypted

format.  When a PIN is presented, it  would  be  encrypted  against  the

format  in  the  data base.  This method requires a method of encrypting

the PIN given at the ATM, until it can be verified at the central  site.

Problems  can  also  occur if the institution wants to move the PIN data

base to another processor, especially from a different computer vendor.





Another  method  is  to take information on the card, combine it with an

institution PIN encryption key (PIN key) and use that  to  generate  the

PIN.   The institution in question used the PIN key method.  This allows

the customer to be verified at the ATM itself and no transmission of the

PIN  is  required.   The  risk  of  the  system  is  the PIN key must be

maintained under the tightest of security.



The PIN key is used to generate the natural PIN.   This  is  derived  by

taking  the  account number and using DES upon it with the PIN key.  The

resulting number then is decimialized by doing a lookup on  a  16  digit

decimalization  table  to  convert  the  resulting hexadecimal digits to

decimal digits.  An ATM loaded with the appropriate  PIN  key  can  then

validate  a customer locally with no need to send PIN information to the

network, thereby reducing the risk of compromise.



The PIN key requires the utmost security.  Once the PIN  key  is  known,

any  customer's  ATM card, with corresponding PIN can be created given a

customer account number.  The ATM allows for the PIN to  be  entered  at

the  ATM  in  two parts, thus allowing each of two bank officers to know

only one half of the key.  If desired, a terminal  master  key  can  be

loaded and then the encrypted PIN key loaded from the network.



The  decimalization table usually consists of 0 to 9 and 0 to 5, ("0" to

"F" in hexadecimal where "F" = 15).  The decimalization table can be put

into any order, scrambling the digits and slowing down an attacker.  (As

a side note, it could be noted that using the "standard" table, the  PIN

digits  are  weighted  to 0 through 5, each having a 1/8 chance of being

the digit, while 6 through 9 has only a 1/16 chance.)



When handling a foreign card, (i.e.  one that does  not  belong  to  the

institution that runs the ATM), the PIN must be passed on to the network

in encrypted form.  First, however, it must be passed from  the  ATM  to

the  ATM controller.  This is accomplished by encrypting the PIN entered

at  the  ATM  using  a  communication  key  (communication   key),   The

communication  key  is  entered  at  the  ATM much like the PIN key.  In

addition, it can be downloaded from the network.  The PIN  is  decrypted

at  the controller and then reencrypted with the network's communication

key.



                                 - 2 -



Security

PIN security

PIN key validation method





Maintaining  the  the  security  of  the  foreign  PIN  is  of  critical

importance.   Given  the  foreign PIN along with the ATM card's magnetic

image, the perpetrator has access to an account  from  any  ATM  on  the

network.    This  would  make  tracking  of  potential  attackers  quite

difficult, since the ATM and the institution they extract funds from can

be  completely  different from the institution where the information was

gleaned.



Given  that  the  encrypted  PIN  goes  through   normal   communication

processes,  it  could  be  logged  on  the normal I/O logs.  Since it is

subject to such logging, the PIN in any form should be denied  from  the

logging function.





3.2.  Security Violations

While  the EFT network has potential to run in a secured mode given some

of the precautions outlined above, the potential for abuse  of  security

is  quite easy.  In the case of this system, security was compromised in

a number of ways, each leading to the potential loss of funds, and to  a

loss of confidence in the EFT system itself.





3.2.1.  Violations of the PIN key method

The  two  custodian  system simply wasn't practical when ATMs were being

installed all over the state.  Two examples show this:   When  asked  by

the  developer  for the PIN key to be entered into a test ATM, there was

first a massive search for the key, and then it was read to him over the

phone.   The  PIN  key  was  written  on  a scrap of paper which was not

secured.  This is the PIN key that all the customer PINs are  based  on,

and which compromise should require the reissue of all PINs.)



The  importance of a system to enter the PIN key by appropriate officers

of the bank should not be overlooked.  In  practice  the  ATM  installer

might  be the one asked to enter the keys into the machine.  This indeed

was demonstrated in this case where the ATM installer not only had  the

keys  for  the  Savings and Loan, but also for other institutions in the

area.  This was kept in the high security area of the  notebook  in  the

installer's front pocket.



Having  a  Master key entered into the ATM by officers of the bank might

add an additional layer of security to the system.  The actual  PIN  key

would then be loaded in encrypted form from the network.  In the example

above, if the installer was aware of the terminal master key,  he  would

have to monitor the line to derive the actual PIN key.



The  use  of  a downline encrypted key was never implemented, due to the

potential complications and added cost of such a  system.   Even  if  it

was,  once violated, security can only be regained by a complete reissue

of customer PINs with the resulting confusion ensuing.







                                 - 3 -



Security

Security Violations

Network validated PIN Security violations





3.2.2.  Network validated PIN Security violations

Given  the  potential  for untraced transactions, the maintenance of the

foreign PINs security was extremely important.  In the PIN  key  example

above,  any  violation  would  directly  affect  the  institution of the

violators.  This would limit the scope of an investigation, and  enhance

the  chance of detection and apprehension.  The violation of foreign PIN

information has a much wider sphere of attack,  with  the  corresponding

lower chance of apprehension.



The  communication  key  itself  was  never  secured.  In this case, the

developer  handed  the  key  to  the  bank  officers,  to   ensure   the

communication  key  didn't get misplaced as the PIN key did (This way he

could recall it in case it got lost).  Given the communication key,  the

security  violation  potential  is  simple enough.  The programmer could

simply  tap  the  line  between  the  ATM  and  the  controller.    This

information  could  then generate a set of PIN and card image pairs.  He

would even have account balances.



Tapping the line would have been an effort, and worse yet he  could  get

caught.   However,  having  the  I/O  logs could serve the same purpose.

While originally designed to obscure PIN information in  the  I/O  logs,

the  feature was disabled due to problems caused by the regional network

during testing.  The I/O logs would be sent to the developer  any  time

there was a problem with the ATM controller or the network interface.



The  generation of PIN and card image pairs has a potential for even the

most secured system on the network  to  be  attacked  by  the  lapse  in

security  of  a weaker node.  Neither the communication key, nor the PIN

should ever be available in the clear.  This requires  special  hardware

at  the  controller  to  store  this  information.   In  this  case, the

institution had no desire to install a  secured  box  for  storing  key

information.   The  communication key was available in software, and the

PIN was in the clear during the process of decrypting from the  ATM  and

re-encrypting  with  the network key.  Any programmer on the system with

access to the controller could put in a log file to tap off the PINs  at

that point.



The largest failure of the system, though, was not a result of the items

described above.  The largest failure in the system was in the method of

encrypting  the  PIN  before  going  to the network.  This is due to the

failure of the network to have a secured key between sites.  The PIN was

to  be  encrypted  with  a  network  key.   The  network key was sent in

encrypted form from the network to the ATM controller.  However, the key

to  decrypt  the network key was sent almost in the clear as part of the

start-of-day sequence.



Any infiltrator monitoring the  line  would  be  able  to  get  all  key

information  by  monitoring the start-of-day sequence, doing the trivial

decryption of the communication key, and proceeding to gather card image

and PIN pairs.  The infiltrator could then generate cards and attack the

system at his leisure.



                                 - 4 -



Security

Security Violations

Network validated PIN Security violations





The network-ATM controller security failure is the most critical feature

since it was defined by a regional network supporting many institutions.

The network was supposedly  in  a  better  position  to  understand  the

security requirements.





4.  The Human Factors in Security  Violation

It is important the users of a system be appraised of the procedures for

securing the system.  They should understand the risks,  and  know  what

they  are  protecting.   The  bank officers in charge of the program had

little experience with ATM systems.  They were never fully indoctrinated

in  the  consequences of a PIN key or communication key compromise.  The

officers showed great surprise when the developer was able  to  generate

PINs  for  supplied  test cards.  Given the potential risk, nothing more

was done to try to change the PIN key,  even  though,  they  were  quite

aware  that  the  PIN  key was in the developer's possession.  They once

even called the developer for the PIN key when they weren't able to find

it.



The  developer  had a desire to maintain a smooth running system and cut

down on the development time of an  already  over-budget  project.   Too

much security, for example modifying I/O logs, could delay the isolation

or repair of a problem.



The regional network was actually a marketing company who  subcontracted

out  the  data processing tasks.  They failed to recognized the security

problem of sending key information with extremely weak encryption.   The

keys  were  all but sent in the clear.  There seemed to be a belief that

the use of encryption in and of itself caused a network to  be  secured.

The  use  of DES with an unsecured communication key gave the appearance

of a secured link.



The lack of audits of the system, both in design and implementation  was

the  final security defect which allowed the system to be compromised in

so many ways.  An example of the Savings and Loan's  internal  auditors

failure  to  understand  the problems or technology is when the auditors

insisted that no contract developers would be  allowed  physically  into

the  computer room.  The fact was, access to the computer room was never

required to perform any of the described violations.





5.  Security Corrections

As in any system where security was required, the time to  implement  it

is  at  the  beginning.  This requires the review of both implementation

and operational plans for the network.  Audits should  be  performed  to

verify  that  the  procedures  are  followed  as  described in the plan.

Financing, scheduling and man power for such audits must be allocated so

security issues can be addressed.



For this institution, the first step would have been to indoctrinate the





                                 - 5 -



Security Corrections



banking  officers  of  the risks in the ATM network, the vulnerabilites,

and the security measures required.





Custodians  of  all  keys should be well aware of their responsibilities

for those keys.  A fall back system of key recovery must be in place  in

case an officer is not available for key entry.



The  cost  of installing hardware encryption units at the host should be

included in the cost of putting in the  system.   The  host  unit  could

generate  down-line  keys for both the PIN key and the communication key

thus making it more difficult to derive  these  keys  without  collusion

from at least three people.



A  secured  communications key should be established between the Network

and the institution.  This would  allow  for  the  exchange  of  working

communication  keys.   This  key  should  be  changed  with a reasonable

frequency.



All these areas should be audited in both the system  specification  and

implementation  to  make sure they are not being abridged in the name of

expediency.





6.  Summary

In this view of a single  institution,  a  number  of  failures  in  the

security  system  were  shown.   There  was  shown a definite failure to

appreciate what was required in the way of security for  PINs  and  keys

used  to  derive  PIN  information.   An avoidance of up front costs for

security lead to potentially higher cost in the future.   The  key  area

was the lack of audits of the EFT system by both the institution and the

network, causing potential loss to all institutions on the network.


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