Browse Prior Art Database

Method for Improving Cryptographic Ciphers Against Power-Analysis Attacks

IP.com Disclosure Number: IPCOM000013787D
Original Publication Date: 2001-Apr-14
Included in the Prior Art Database: 2003-Jun-18
Document File: 4 page(s) / 36K

Publishing Venue

IBM

Abstract

A novel approach to secure the implementations of security-sensitive applications using cryptographic means implemented on hardware tokens susceptible to external power-analysis attacks is described. In particular, two complemental techniques are presented that thwart a class of attacks known as Differential Power Analysis (DPA) against smart cards. An example is given of how these techniques can be applied in a non-invasive way to an existing e-cash protocol.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 30% of the total text.

Page 1 of 4

Method for Improving Cryptographic Ciphers Against Power-Analysis Attacks

  A novel approach to secure the implementations of
security-sensitive applications using cryptographic means
implemented on hardware tokens susceptible to external
power-analysis attacks is described. In particular, two
complemental techniques are presented that thwart a class of
attacks known as Differential Power Analysis (DPA) against smart
cards. An example is given of how these techniques can be applied
in a non-invasive way to an existing e-cash protocol.

Background

A smart card is a hardware token the size of a credit card. It
bears a microprocessor executing instructions controlled by some
control software loaded in its internal memory. In order to
execute security-sensitive applications like handling electronic
cash or performing login operations, a smart card typically
contains software or hardware implementing cryptographic
algorithms. Due to the size and cost constraints of a smart card,
no card-internal power source is typically present on a card.
Therefore, all power for executing the instructions on the smart
card has to be provided by the card-external world, so-called
smart card terminals.

Problem solved

The environment of a smart card as described above facilitates a
class of attacks against smart card hardware known as
(differential) power-analysis (DPA). In this attack, a malicious
agent monitors the power consumption of the smart card in a very
thorough way: Power-usage samples are taken every few
microseconds. The basics of this attack is the knowledge that any
smart card hardware 'leaks' some information about the machine
instructions executed at any one time, as every machine
instruction has a typical power-consumption pattern. The amount
of information leakage differs widely for different smart card
hardware, necessitating different approaches to protecting a
particular hardware against DPA attacks. Given these
prerequisites, it is now possible to match the appearing patterns
of executed machine instructions to typical patterns of
well-known algorithms. As the implementation of a cryptographic
cipher like DES is typically well known, and exhibits a
particular power-consumption pattern, given sufficient samples,
skilled attackers can derive the cryptographic keys used in these
operations. This is one of the most dangerous attacks currently
known to smart cards, as the secrecy of the crypto-graphic keys
safeguards the security of all smart card aware applications like
e-cash systems, computer login procedures, or signature

1

Page 2 of 4

operations.

The method described in this disclosure shows a simple, yet novel
approach to protecting a smart card from this class of attacks to
its integrity.

Proposed solution: Counting key usage and internal key derivation

The suggested solution is a two-fold one: Protecting the smart
card from negative and positive DPA attacks. Under negative
attacks, one understands trials to execute a cryptographic
algorithm without the knowledge of the actu...