Decimalization table attack
Encyclopedia
A decimalization table attack is a technique that may allow a corrupt insider at a bank to discover Personal Identification Number
s (PINs) by exploiting a design flaw in the Hardware Security Module
used to protect the PIN.
PINs for payment card
s are usually generated by encrypting the card number under a secret key held securely by the issuing bank. The encryption produces a hexadecimal
value with digits in the range 0 to 9 and A to F. A decimalization table is then used to convert this value to a PIN with digits in the range 0 to 9, for instance mapping A to 0, B to 1, etc.
When a transaction is authorized, the PIN is verified when the bank's software sends the encrypted PIN to a hardware security module (HSM). The HSM then indicates whether the PIN was correct or not.
Some HSMs require the bank's software to send the decimalization table to the HSM. A decimalization table attack is the technique where a corrupt insider with access to the bank's HSM manipulates the decimalization table in order to guess the PIN more rapidly than should otherwise be possible.
In 2002 two PhD students at Cambridge University
, Piotr Zieliński and Mike Bond, discovered a decimalization table attack in the PIN verification system of the IBM 3624
, which was duplicated in most later hardware. The attack allowed someone who has access to a bank's computer system to determine the PIN for an ATM card
in an average of 15 guesses, instead of the average 5000 guesses expected for a 4-digit PIN.
This type of attack is known as an API attack because it relies on exploiting a weakness in the Application Programming Interface
(API) of the HSM.
Personal identification number
A personal identification number is a secret numeric password shared between a user and a system that can be used to authenticate the user to the system. Typically, the user is required to provide a non-confidential user identifier or token and a confidential PIN to gain access to the system...
s (PINs) by exploiting a design flaw in the Hardware Security Module
Hardware Security Module
A hardware security module is a type of secure cryptoprocessor targeted at managing digital keys, accelerating cryptoprocesses in terms of digital signings/second and for providing strong authentication to access critical keys for server applications...
used to protect the PIN.
PINs for payment card
Payment card
The term payment card covers a range of different cards that can be presented by a cardholder to make a payment.-Types:Typically a payment card is backed by an account holding funds belonging to the cardholder, or offering credit to the cardholder. Payment cards can be classified into types...
s are usually generated by encrypting the card number under a secret key held securely by the issuing bank. The encryption produces a hexadecimal
Hexadecimal
In mathematics and computer science, hexadecimal is a positional numeral system with a radix, or base, of 16. It uses sixteen distinct symbols, most often the symbols 0–9 to represent values zero to nine, and A, B, C, D, E, F to represent values ten to fifteen...
value with digits in the range 0 to 9 and A to F. A decimalization table is then used to convert this value to a PIN with digits in the range 0 to 9, for instance mapping A to 0, B to 1, etc.
When a transaction is authorized, the PIN is verified when the bank's software sends the encrypted PIN to a hardware security module (HSM). The HSM then indicates whether the PIN was correct or not.
Some HSMs require the bank's software to send the decimalization table to the HSM. A decimalization table attack is the technique where a corrupt insider with access to the bank's HSM manipulates the decimalization table in order to guess the PIN more rapidly than should otherwise be possible.
In 2002 two PhD students at Cambridge University
University of Cambridge
The University of Cambridge is a public research university located in Cambridge, United Kingdom. It is the second-oldest university in both the United Kingdom and the English-speaking world , and the seventh-oldest globally...
, Piotr Zieliński and Mike Bond, discovered a decimalization table attack in the PIN verification system of the IBM 3624
IBM 3624
A successor to the IBM 3614, the IBM 3624 was a late 1970s second-generation Automatic teller machine that was designed at the IBM Los Gatos lab. IBM 3624 units, along with the later IBM 4732, were manufactured at IBM facilities in Charlotte, North Carolina and Havant, England until all operations...
, which was duplicated in most later hardware. The attack allowed someone who has access to a bank's computer system to determine the PIN for an ATM card
ATM card
An ATM card is a card issued by a bank, credit union or building society that can be used at an ATM for deposits, withdrawals, account information, and other types of transactions, often through interbank networks.Some ATM cards can also be used:* at a branch, as identification for in-person...
in an average of 15 guesses, instead of the average 5000 guesses expected for a 4-digit PIN.
This type of attack is known as an API attack because it relies on exploiting a weakness in the Application Programming Interface
Application programming interface
An application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...
(API) of the HSM.