ISO/IEC 20085-1:2019

INTERNATIONAL ISO/IEC
STANDARD 20085-1
First edition
2019-10
IT Security techniques — Test tool
requirements and test tool calibration
methods for use in testing non-
invasive attack mitigation techniques
in cryptographic modules —
Part 1:
Test tools and techniques
Techniques de sécurité IT — Exigences de l'outil de test et méthodes
d'étalonnage de l'outil de test utilisées pour tester les techniques
d'atténuation des attaques non invasives dans les modules
cryptographiques —
Partie 1: Outils et techniques de test
Reference number
©
ISO/IEC 2019
© ISO/IEC 2019
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ii © ISO/IEC 2019 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 3
5 Test tools . 3
5.1 General . 3
5.2 Types of side-channels . 4
5.2.1 General. 4
5.2.2 Power consumption . 4
5.2.3 Electromagnetic emissions . 4
5.2.4 Computation time . 4
5.3 Categorization of test tool . 4
5.4 Test tool components . 5
5.4.1 General. 5
5.4.2 Measurement tool . 5
5.4.3 Analysis tool . 7
5.4.4 Functional items of test tools components . 7
6 Test techniques and associated approaches . 8
6.1 Operation . 8
6.2 Interaction between the measurement tool and the IUT . 9
6.3 Interaction between the analysis tool and the IUT . 9
6.4 Interaction between the analysis tool and the measurement tool . 9
Annex A (informative) Selection of test methods and approaches .10
Annex B (informative) Example of measurement tool .15
Annex C (informative) Data exchange and storing technologies .17
Bibliography .18
© ISO/IEC 2019 – All rights reserved iii

Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that
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This document was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 27, Information security, cybersecurity and privacy protection.
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iv © ISO/IEC 2019 – All rights reserved

Introduction
Cryptographic modules provide cryptographic services and protect critical security parameters
(CSPs). Protection of CSPs can either be logical, physical, or both. However, information such as
knowledge of CSPs can leak out of the cryptographic module when manipulated, if the module is
not designed to mitigate such leakage. Without mitigation, a malicious attacker can record available
side-channel leakage. This leakage is a physical quantity related to the CSPs and can be analysed in a
manner to extract knowledge of those parameters. Such analysis is passive, in that it simply collects
the side-channel leakage utilizing measurement apparatus which is freely available. Notice that the
measurement tool can be adaptively controlled. This kind of extraction and analysis is referred to as
non-invasive. Techniques which allow the extraction of CSPs out of this non-invasive leakage is termed
an “attack” on the module.
This document focuses on the measurement and analysis of side-channel information. Side-channel
non-invasive test tools can be automated to collect such leakage. To characterize the quality of the
test tools, metrics are needed, such as signal-to-noise ratio (S/N) (described in ISO/IEC 20085-2).
ISO/IEC 20085 (all parts) addresses the measurement and analysis techniques. Those are automated in
a test tool. The functionality and the operation of a test tool are described in ISO/IEC 20085 (all parts).
© ISO/IEC 2019 – All rights reserved v

INTERNATIONAL STANDARD ISO/IEC 20085-1:2019(E)
IT Security techniques — Test tool requirements and test
tool calibration methods for use in testing non-invasive
attack mitigation techniques in cryptographic modules —
Part 1:
Test tools and techniques
1 Scope
This document provides specifications for non-invasive attack test tools and provides information
about how to operate such tools. The purpose of the test tools is the collection of signals (i.e. side-
channel leakage) and their analysis as a non-invasive attack on a cryptographic module implementation
under test (IUT).
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO/IEC 19790:2012, Information technology — Security techniques — Security requirements for
cryptographic modules
3 Terms and definitions
For the purposes of this document, the terms and definitions given ISO/IEC 19790 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
advanced side-channel analysis
ASCA
advanced exploitation of the fact that the instantaneous side-channels emitted by a cryptographic
device depends on the data it processes and on the operation it performs to retrieve secret parameters
Note 1 to entry: Not to be confused with algebraic side-channel analysis (SCA).
Note 2 to entry: The adjective “advanced”, opposed to “simple”, qualifies side-channel analyses which require
multiple side-channel measurements (see 6.2).
[SOURCE: ISO/IEC 17825:2016, 3.1, modified — Notes to entry have been added.]
3.2
analysis tool
test tool component with the ability to control the measurement process, read the recorded
measurements, perform post-processing of the recorded measurements, and identify any valid attacks
© ISO/IEC 2019 – All rights reserved 1

3.3
application-specific tool
tool dedicated to the measurements and analyses required by ISO/IEC 20085 (all parts)
Note 1 to entry: Antonym of laboratory-assembled tool.
3.4
batch measurement
measurement that includes signals related to repeated execution of one cryptographic operation with
a single or with different inputs
Note 1 to entry: See Figure A.1.
3.5
cartography
procedure involving placing a sensor at various positions and taking measurements at each of them to
create a spatial (or visual) representation of some data
Note 1 to entry: See A.8.
3.6
horizontal attack
HA
modus operandi where sensitive information is extracted from a single measurement split into
several parts
Note 1 to entry: The single measurement can be an averaged measurement obtained from a batch of
measurements where repeated operations are conducted with the same cryptographic inputs.
[SOURCE: ISO/IEC 17825:2016, 3.8, modified — Note to entry has been added.]
3.7
implementation under test
IUT
implementation which is tested based on methods specified in ISO/IEC 17825:2016
[SOURCE: ISO/IEC 17825:2016, 3.9, modified — The words “in this International Standard” have been
replaced with “in ISO/IEC 17825:2016”.]
3.8
laboratory assembled tool
tool made by assembly of commercial off-the-shelf (COTS) products
Note 1 to entry: Antonym of application-specific tool (3.3).
3.9
measurement tool
test tool component with the ability to measure signals in digital format (scalar or vector), time-
synchronized with a trigger signal, and that records permanently or transiently the measurements for
subsequent analysis
3.10
multivariate trace
trace made up of several samples
EXAMPLE The measurement of an electromagnetic field over time is a multivariate trace.
Note 1 to entry: Usually, a “trace” is considered multivariate.
2 © ISO/IEC 2019 – All rights reserved

3.11
non-invasive attack
attack that can be performed on a cryptographic module without direct physical contact with
components within the cryptographic boundary of the module
Note 1 to entry: An attack that does not alter or change the state of the cryptographic module.
[SOURCE: ISO/IEC 19790:2012, 3.78]
3.12
signal-to-noise ratio
S/N
measure that compares the level of a desired signal to the level of background noise
Note 1 to entry: It is defined as the ratio of signal power to the noise power.
[SOURCE: ISO/IEC 27033-6:2016, 3.8, modified — The abbreviated term has been added.]
3.13
univariate trace
trace made up of one sample
EXAMPLE A measurement of duration is a univariate trace.
3.14
vertical attack
VA
modus operandi where sensitive information is extracted from different algorithm executions
Note 1 to entry: If the algorithms executions are the same, then the traces can be averaged in a view to increase
their signal-to-noise ratio (3.12), and then a horizontal attack (3.6) can be carried out.
Note 2 to entry: The definition is equivalent to: “Modus operandi where sensitive information is extracted from
measurements of repeated execution of one cryptographic operation with different inputs".
[SOURCE: ISO/IEC 17825:2016, 3.17, modified — Notes to entry have been added.]
4 Symbols and abbreviated terms
For the purposes of this document, the symbols and abbreviated terms given in ISO/IEC 19790 and the
following apply.
API Application Programming Interface
COTS Commercial Off-The-Shelf
CSP Critical Security Parameter
SPA Simple Power Analysis
5 Test tools
5.1 General
ISO/IEC 20085 (all parts) relates to ISO/IEC 17825:2016, which specifies the non-invasive attack
mitigation test metrics for determining conformance to the requirements specified in ISO/IEC 19790
for Security Levels 3 and 4. The test metrics are associated with the security functions specified in
ISO/IEC 19790.
© ISO/IEC 2019 – All rights reserved 3

This document also relates to ISO/IEC 20085-2, which details how the test tool shall be calibrated, to
adjust to the requirements (threshold values, for Security Levels 3 and 4) of ISO/IEC 17825.
5.2 Types of side-channels
5.2.1 General
ISO/IEC 17825:2016, Clause 6, specifies three types of side-channels concerned with non-invasive
attacks, namely:
a) the power consumption of the IUT,
b) the electromagnetic emissions of the IUT, and
c) the computation time of the IUT.
These side-channels are represented in Figure 1, and are addressed in the Introduction, 5.2.2, 5.2.3 and
5.2.4. These side-channels are measured passively insofar as the IUT behaviour is not disturbed by the
measurement tool.
Figure 1 — Three types of side-channels
Other types of side-channels are emerging (see ISO/IEC 17825:2016, B.6).
5.2.2 Power consumption
The power side-channel can be measured by various means. Power measurements are typically
measured as a voltage difference.
5.2.3 Electromagnetic emissions
The measurement is indicated by a voltage difference measured by an antenna. Therefore, the
measurement can be carried out remotely, and without contact with the cryptographic module.
5.2.4 Computation time
The measurement is indicated by a difference of timing for the selected cryptographic operation,
obtained as the subtraction of times corresponding to the cryptographic resources to triggers (start
and end).
5.3 Categorization of test tool
Test tools can be broadly categorized in two types: "Laboratory Assembled", and "Application Specific".
— For Laboratory Assembled tools the non-invasive attack test tool is assembled from two or more
commercial off-the-shelf (COTS) products, each of which can have another purpose in the laboratory.
4 © ISO/IEC 2019 – All rights reserved

— Application Specific tools, which can also be available as COTS products are dedicated to the
measurements and requirements of ISO/IEC 20085 (all parts). They cannot be used for other
laboratory testing tasks.
NOTE A test tool is not necessarily a crafted tool. It can be built from parts of equipment used in other
contexts.
5.4 Test tool components
5.4.1 General
A test tool is made up of two components: a measurement tool and an analysis tool. Their requirements
are detailed in this subclause.
5.4.2 Measurement tool
Measurement tools are required to collect the side-channel emanations from the IUT. There shall be
at least two measures: time (horizontal side-channel) and voltage/electromagnetic field (vertical side-
channel).
The measurement tools can be two distinct tools i.e. a timer and a digitizer. Both functions can be
presented by a single tool (e.g. an oscilloscope), which is able to measure vertical quantities as well as
timing as a "function" feature. Such a setup can perform all the tests found in ISO/IEC 20085 (all parts)
serially without the need for hardware setup reconfiguration. The single-tool solution is recommended
as more convenient for the tester and supports accuracy since the experimental conditions are
maintained unchanged during the whole test procedure.
Such measurement tool shall reflect the internal operations carried out within the IUT. For instance,
the horizontal side-channel shall relate to the number of required computations, while the vertical
side-channel shall show up when a critical security parameter (CSP) is used. In this second case, the
CSP can directly influence the vertical side-channel, or indirectly, e.g. because it is mixed with parts of
the plaintext/ciphertext (assuming the operation is a symmetrical encryption).
Horizontal side-channel can be measured as the duration between a request and a response. However,
unpredictable latency can decrease the S/N of such measurement. A more accurate option consists in the
derivation of the operation duration from a vertical side-channel trace. In this case, the actual duration
[5]
can be measured . The sensor involved is a timer. The test requirements listed in ISO/IEC 17825
demand a resolution less than or equal to the clock frequency of the cryptographic module making up
or embedded in the IUT.
Vertical side-channel can be measured either globally or locally. Global vertical side-channel
measurement consists in the acquisition of an aggregate quantity, e.g. the total power consumption of the
whole IUT. This method is well suited for single-chip modules. Local vertical side-channel measurement
consists in using a sensor smaller than the IUT, which is placed at various locations around or inside the
IUT, where the S/N is stronger. This procedure is referred to as a cartography (see details in A.8). It is a
preferred method for the localization of the leakiest position in the case the IUT is a multi-chip module.
The sensor shall be able to probe leaked information without tampering with the IUT.
Examples of such sensors are:
— an antenna (microscopic, mesoscopic or macroscopic) which measures the electromagnetic field
emitted by the IUT;
— a current probe placed on the communication or power cables of the IUT can measure leakage
[6]
outside the boundary of the IUT .
An illustration of horizontal versus vertical attacks, and univariate traces versus multivariate traces, is
given in Figure 2.
© ISO/IEC 2019 – All rights reserved 5

Figure 2 — Illustration of vertical versus horizontal attacks, and multivariate versus univariate
side-channel traces
Horizontal side-channel analysis shall be performed with one single measurement and shall be collected
as noise-free as possible. Such analyses include asymmetric cryptography where the security parameter
is updated upon each cryptographic operation, or symmetrical cryptography which can be analysed
using a profiled attack (also known as a "template" attack). Regarding vertical side-channel analysis,
the S/N can be enhanced by adding more traces. If the noise is independent from one measurement
to the next, the S/N (in power) increases linearly with the number of measurements. Therefore, setup
quality can be traded for more measurements in vertical side-channel analysis. In addition, vertical
side-channel analyses require traces to be properly aligned, otherwise the contrast of the analysis is
reduced. The traditional modus operandi when both horizontal and vertical analyses are prescribed:
— first a horizontal analysis is carried out: if the control flow depends on the key, then it is likely to be
exploitable at this stage;
— otherwise, the control flow does not depend on the key material, therefore traces are (by design)
aligned, which is a favorable situation for vertical side-channel analyses.
Environmental conditions shall be carefully monitored during the measurements. The external
environment conditions shall be controlled as they can influence the side-channel emanation changes
during the measurements; temperature and supply voltage shall be monitored as specified in
ISO/IEC 19790:2012, 7.7.4.3. The measurement tool shall be stable. For example, some oscilloscopes
require some warm up time after power-up to carry out reproducible and accurate measurements.
Symmetrically, the IUT shall be powered up sufficiently in advance so that it has reached a stable state,
allowing for measurements with as little trend noise as possible.
An example of measurement tool and its attributes can be found in Annex B.
Measurement of power consumption (see 5.2.1), electromagnetic emanations (see 5.2.2) and
computation time can be carried out as explained below.
a) Power consumption measurements are carried out across a current probe or a conductor that is
inserted between the measurement ground (or voltage supply) and that of the IUT. The conductor
can be a resistor (or, respectively, a capacitance, or an impedance), in which case the measurement
is a voltage difference, proportional to the current drawn by the resistance (or, respectively,
proportional to its integral or derivative). The acquired signal can be amplified. Depending on the
targeted algorithm, the trace:
1) can focus on the first (or the last) clock cycles of the cryptographic operation [case of ASCA on
symmetric encryption, where the plaintext (or the ciphertext) is known];
6 © ISO/IEC 2019 – All rights reserved

2) encompasses the whole operation, as is the case of HA on asymmetric cryptography.
b) As for power consumption, the electromagnetic signal can be amplified. The location of probe is an
important parameter. In a view to optimize the S/N, a cartography can be done. It can scan over the
chip die, or the whole printed circuit board (PCB), including decoupling capacitors.
c) Computation time measurement can be carried out in a variety of way. A first option is the timing
difference between the time when the operation is launched, and result is returned. A second
option is the timing difference between the cryptographic modules start and stop, observed for
instance from a multivariate side-channel trace, be it power or electromagnetic side-channel. In
this respect, the measurement consists in a post processing of a power or of an electromagnetic
emission measurement.
5.4.3 Analysis tool
The analysis tool is made up of three components.
The first component controls the measurement process. This is an automation task which can be
implemented in several ways e.g. through a scripting language or through use of a more advanced
program. This control can simply request traces sequentially. However, when a large number of
measurements is required, batch measurement can be useful (refer to A.7).
The second component is data post-processing where the recorded measurements are conditioned to:
— remove abnormal traces (clearly invalid traces identified as outliers are filtered out);
[9]
— alignment using points of interest within the traces (this step is natural for vertical attacks;
however, it is also beneficial to horizontal attacks when the trace is obtained from an averaging of
identical operations);
— reduce the dimensionality, thanks to principal components analysis (PCA), linear discriminant
analysis (LDA) or variance tests [for data compression, statistics (e.g. probability density function)
simplification, and computation load alleviation];
— allow for data fusion, especially in the case of multi-sensor or multiple modality (e.g. power and
[3] [4]
electromagnetic field concomitant measurements, refer to Bibliographic references and ).
Such post-processing is typically carried out by a software program. It can require a caching of the
measurements. The purpose of the cache is to provide a local temporary storage of part, or all, of the
measurements.
The third component analyses the post-processed data in order to identify any valid attacks. The
methodology is explained in ISO/IEC 17825. The goal of this tool is to verify that the measurement and
the analysis were carried out properly. It consists in a CSP recovery attack, wh
...