=Paper=
{{Paper
|id=Vol-1844/10000727
|storemode=property
|title=Usable Security Versus Secure Usability: an Assessment of Attributes
Interaction
|pdfUrl=https://ceur-ws.org/Vol-1844/10000727.pdf
|volume=Vol-1844
|authors=Oleksandr Gordieiev,Vyacheslav Kharchenko,Kate Vereshchak
|dblpUrl=https://dblp.org/rec/conf/icteri/GordieievKV17
}}
==Usable Security Versus Secure Usability: an Assessment of Attributes
Interaction==
https://ceur-ws.org/Vol-1844/10000727.pdf
Usable Security Versus Secure Usability:
an Assessment of Attributes Interaction
Oleksandr Gordieiev1, Vyacheslav Kharchenko2 and Kate Vereshchak3
1Banking University, 1 Andriivska Street, Kyiv, Ukraine
alex.gordeyev@gmail.com
2National Aerospace University «KhAI», 17 Chkalova Street, Kharkiv, Ukraine
V.Kharchenko@csn.khai.edu
3Luxoft, 10/14 Radisheva Street, Kyiv, Ukraine
vereshchak@gmail.com
Abstract. Attributes of information systems quality described in standard
ISO/IEC25010 (2010) are analyzed. Some of them are contradictory,
dependent and competing. One of the most competing characteristics are
usability and security (U&S). The article considers two main aspects of U&S
interaction called “usable security” and “secure usability”. The technique of
qualitative assessment of the U&S interaction based on analysis of
subcharacteristics and metrics is suggested. An example of the technique
application to assess U&S interaction for university web-site is discussed.
Keywords. Usability and security interaction, usable security, secure usability
ISO/IEC25010, ISO/IEC25023
Key Terms. Usability, security, software characteristics, software metrics,
interaction
1 Introduction
1.1 Motivation
Information systems are characterized by a set of characteristics/attributes that are
defined by international standards. The standard ISO/IEC 25010 «System and
software quality model» [1] defines the following 10 characteristics of information
systems: functional suitability, performance efficiency, compatibility, usability,
reliability, security, maintainability, portability. Such nomenclature was formed in
result their evolution during about 60 years [2]. Certain characteristics
(subcharacteristics) of information systems interact at each other. I.e. there are
situations when strengthening (weakening) of one of the characteristics requires or
generates strengthening (weakening) of another or even a group of information
systems. In the article we will consider a couple of the most important, mutually
influence and competitive characteristics – usability and security (U&S).
1.2 State of Art
First of all, we need give of description for U&S attributes. Usability – degree to
which a product or system can be used by specified users to achieve specified goals
with effectiveness, efficiency and satisfaction in a specified context of use [1].
Security - degree to which a product or system protects information and data so that
persons or other products or systems have the degree of data access appropriate to
their types and levels of authorization [1]. Information systems must have of Usability
and Security characteristics, because they must be comfortable in use and secure
simultaneously. Depending on field of information systems application, levels of
U&S requirements and characteristic values are not the same. In most cases,
information systems are more usable, including at the expense of security, or more
secure at the expense their usability.
Problems of U&S characteristics interaction are well known, researched and
presented in materials of conferences, in articles and books. Analysis of works in this
field gave us possibility make some conclusions and divide of accessible works on
following groups in some fields:
most part of works are about concrete problems in U&S field and mechanisms
for their solutions [3, 4, 5, 6, 7]. In particular, in [3] are viewed alphanumeric
passwords problems and are presented ways for their decision;
following group of works about general conceptual questions in the U&S field
[8, 9];
part of works about problems and peculiarities of U&S interaction on required
levels [6], on processed levels [10, 11] and on model levels (including UML models)
[12];
small group includes works about U&S problems for mobile applications
[13,14];
separate works about analysis of literature in U&S problems field [15];
some articles about U&S characteristics evolution. Authors of such works
represent the evolution and interaction of usability and security characteristics [16, 2].
1.3 Goal and Structure
Preliminary analysis of works in U&S field permitted to make the following
conclusions and determine goal of the paper:
firstly, characteristics of U&S which described in last program engineering
standards [1, 17, 18] are one from other results of 40 years evolution [2, 16]. They
represented as complex characteristics with set of depended subcharacteristics;
secondly, analysis of U&S subcharacteristics and metrics did not conduct in
existing works [3-16], which describe problems interaction of U&S characteristics;
thirdly, separate subdivision was organized at National Institute of Standards
and Technology (NIST) of USA [20], which solves tasks of U&S interaction.
However, well known works describe, first of all, influence of Usability on Security
and did not take into account aspects of influence on level of their subcharacteristics.
Thus, goal of article is determination, analysis and assessment of U&S interaction
on subcharacteristics and metrics levels.
The paper has the following structure. Main second section contains:
description of "Usable security" and "Secure usability" interaction problem;
analysis of U&S interaction on subcharacteristics level and variants U&S
subcharacteristics interaction;
analysis of U&S interaction on metrics level.
The third section analyses and assesses U&S interaction for university web-site and
the fourth section concludes and describes directions of the future research.
2 Usability and Security
2.1 Two Sides of the Same Coin
Exist of two possible aspects of research and development (i.e. two sides of the same
coin): usable security and secure usability. Let’s consider in more details what are the
differences between these two aspects.
Usable Security
First aspect gives an answer on a question: how to develop functions secure access to
resources such, in order to ensure acceptable/necessary level of usability of user
interfaces. In order to link of U&S characteristics in the usable security aspect was
more understandable, we need represent example of such an interaction. Very often
procedure of registration on web-site requires from users to confirm their presence
near personal computer. It needs to exclude automatic registration on the Internet. As
a rule, web-site offers to users input data for CAPTCHA
(Completely Automated Public Turing test to tell Computers and Humans Apart)
[20]. In majority of cases, the CAPTCHA is information, which automatic generator
on picture of web-page and which necessary input to textbox. Sometimes users have
problems with input of information from CAPTCHA (i.e. have problem with Public
Turing test), because information which is represented on picture periodically cannot
be discernible. (Fig. 1). Defect of such technique of identification can provoke
discomfort for user. For solution of such problem user necessary, periodically
manually reload the picture of CAPTCHA waiting for recognizable information. User
can wait long time of appearance recognizable information. User can also delay or
cancel, for example, web-site registration procedure. This is an example, when
«complex» security kills usability – (cSkU) Information systems developers necessary
take into account such aspect, when they make project of user interfaces. We have to
exclude situation, when high level of security «kills» the usability.
It should be noted, that subdivision at National Institute of Standards and
Technology (NIST) of USA researches such U&S problems [19].
Fig. 1. Examples of CAPTCHAs.
Secure Usability
Second aspect has relationships with development of user interfaces thus, in order to
ensure necessary level of information security. Lets describe an example of such
interaction between usability and security. Public Turing test can be maximum simple
and represents one checkbox element, which necessary will set up in significance
«check» (Fig. 2). From usability position such variant of Public Turing test is more
better than his variant on Fig 1. But from security position such variant (Fig. 2) is
more worse, because as against previous variant (Fig. 1) such variant is more simply
pass (by software bots) during automatic registration without user. In other words, in
such a context there is another competition. This is situation, when «simple» usability
“kills” security – sUkS).
Fig. 2. More simple Public Turing test.
2.2 Criteria
General
Thus, U&S characteristics really have interconnection in the form of two aspects and
formally differences can be described through «castle» of objective function and
limitations.
in first case it is necessary to ensure the required level of usability (Ureq), at
that maximize of security (Smax), i.e. S →max, U ≥ Ureq;
in second case it is necessary ensure the required level of security (Sreq), at
that maximize of usability (Umax), i.e. . U→ max, S ≥ Sreq.
We pay attention, that U&S characteristics and their sub characteristics described
in article as their interpretation in group of standards ISO 25000.
Attributes of Security and Usability
Examined positions can be represented out in detail as:
security – is combination of following subcharacteristics [1]: confidentiality,
integrity, non-repudiation, accountability and authenticity
S = {Conf, Integr, N-rep, Acc, Aut};
usability – is combination of following subcharacteristics [1]: appropriateness
recognizability, learnability, operability, user error protection, user interface
aesthetics, accessibility.
U = {AppRec, Learn, Oper, UEP, UIA, Acs}.
2.3 U&S Subcharacteristics Interaction Analysis
We will consider interaction between U&S subcharacteristics. For that we will
describe more detail formulations their subcharacteristics [1], which represented in
table 1.
Table 1. U&S subcharacteristics formulations.
№ Characteristics
Description
(subcharacteristics)
degree еto which a product or system can be used
by specified users to achieve specified goals with
1 Usability
effectiveness, efficiency and satisfaction in a
specified context of use
Appropriateness degree to which users can recognize whether a
1.1
recognizability product or system is appropriate for their needs
degree to which a product or system can be used
by specified users to achieve specified goals of
1.2 Learnability learning to use the product or system with
effectiveness, efficiency, freedom from risk and
satisfaction in a specified context of use
degree to which a product or system has attributes
1.3 Operability
that make it easy to operate and control
degree to which a system protects users against
1.4 User error protection
making errors
User interface degree to which a user interface enables pleasing
1.5
aesthetics and satisfying interaction for the user
degree to which a product or system can be used
1.6 Accessibility
by people with the widest range of characteristics
and capabilities to achieve a specified goal in a
specified context of use
NOTE 1 The range of capabilities includes
disabilities associated with age.
NOTE 2 Accessibility for people with disabilities
can be specified or measured either as the extent
to which a product or system can be used by
users with specified disabilities to achieve
specified goals with effectiveness, efficiency,
freedom from risk and satisfaction in a specified
context of use, or by the presence of product
properties that support accessibility.
degree to which a product or system protects
information and data so that persons or other
products or
2 Security
systems have the degree of data access
appropriate to their types and levels of
authorization
degree to which a product or system ensures that
2.1 Confidentiality data are accessible only to those authorized to
have access
degree to which a system, product or component
2.2 Integrity prevents unauthorized access to, or modification
of, computer programs or data
degree to which actions or events can be proven
2.3 Non-repudiation to have taken place, so that the events or actions
cannot be repudiated later
degree to which the actions of an entity can be
2.4 Accountability
traced uniquely to the entity
degree to which the identity of a subject or
2.5 Authenticity
resource can be proved to be the one claimed
We have received set of variants of U&S subcharacteristics interaction because of
U&S subcharacteristics analysis. Set of variants of U&S subcharacteristics represents
table 2.
We will comment received variants. First of all, we will set the numeration as two
numbers (from table 2), which includes the first number as usability characteristic and
the second number as security characteristic:
1-1. Appropriateness recognizability subcharacteristic has interaction with
confidentiality subcharacteristic. It is obvious, because before ensuring
`Confidentiality`, user must, for example, see text boxes for input confidential
information and inputted such information;
1-2, 1-3, 1-4, 1-5. In authors opinion, such variants of interaction between
U&S characteristics are possible, but they require additional research for set up more
exact of interaction type;
Table 2. Variants of interaction of U&S subcharacteristics.
Authenticity
Confidentiality
Accountability
Integrity
repudiation
Non-
Usability characteristics/
№
Security characteristics
1 2 3 4 5
1 Appropriateness
↑↑/↓↓ ? ? ? ?
recognizability
2 Learnability ↑↓ – – – –
3 Operability ↑↑/↓↓ ↑↑/↓↓ ↑↑/↓↓ ↑↑/↓↓ ↑↑/↓↓
4 User error
↑↑/↓↓ ↑↑/↓↓ ↑↑/↓↓ ↑↑/↓↓ ↑↑/↓↓
protection
5 User interface
↑↑/↓↓ ? ? ? ?
aesthetics
6 Accessibility ↑↓ ↑↓ ↑↓ ↑↓ ↑↓
– - interaction is absent;
↑↑ - increase of level of one characteristic incurring to increase of
level of other characteristic;
↑↓ - increase of level of one characteristic incurring to decrease of
level of other characteristic;
↓↓ - decrease of level of one characteristic incurring to decrease of
level of other characteristic;
? - interaction is exist, but type of interaction to set very difficult
(exist necessity of additional research)
2-1. Such variant of interaction between subcharacteristics Learnability and
Confidentiality exists, because if user receives more information abaut
Confidentiality, than the level will be lower. Thus, if level of Learnability will
increase, level of Confidentiality will decrease. And vice versa, if level of
Learnability will decrease, level of Confidentiality will increase;
2-2, 2-3, 2-4, 2-5. In authors opinion, such variants of interaction between
subcharacteristics are absent;
3-1, 3-2, 3-3, 3-4, 3-5. Such variants of interaction between subcharacteristics
of Operability and Confidentiality, Integrity, Non-repudiation, Accountability,
Authenticity exist, because of increase of Operability level leads to increase in such
subcharacteristics, and vice versa, because of decrease of Operability level leads to
decrease such subcharacteristics;
4-1, 4-2, 4-3, 4-4, 4-5. Variants of interaction between User error protection
and Confidentiality, Integrity, Non-repudiation, Accountability, Authenticity exist,
because decrease of count of user errors incurring to increase of level of
characteristics Confidentiality, Integrity, Non-repudiation, Accountability and
Authenticity, but increase of count of user errors incurring to decrease their level;
5-1. User`s interface aesthetics subcharacteristic has interaction with
Confidentiality subcharacteristic, because, when user works with information systems
interface, which has attractive design and well tidy colors, user has esthetical
satisfaction, consequently, he can see textboxes for input confidential information and
input her;
5-2, 5-3, 5-4, 5-5. In authors opinion, such variants of interaction between
U&S subcharacteristics are possible, but require additional research for set up more
exact of interaction type;
6-1, 6-2, 6-3, 6-4, 6-5. In this variants if the level of Accessibility
characteristic will increase then levels of all subcharacteristics of security
characteristic will decrease and vice versa, if level of Accessibility characteristic will
decrease then levels of all subcharacteristics of security characteristic will increase. It
is obvious, because of ensuring of Accessibility characteristic in information systems
for people with disabilities in user`s interfaces it is necessary to do coordinal redesign
of user interfaces. As a rule, such redesign of interfaces, on the one hand, lighten of
interaction with software for people with disabilities, on the other hand, it is source of
level decrease for all subcharacteristics of security characteristic.
2.4 U&S Metrics Analysis
We will analyze of U&S metrics. For that, first of all, we will represent short
description of metrics and primitives (table 3).
Table 3. Brief description of U&S metrics.
Characteristics/
№ Name of metric Description Primitives
Subcharacteristics
1. Description What proportion A= Number of functions Usability/
completeness of functions (or types of functions) Appropriateness
(or types of described as recognisability
function) are understandable in the
described as product description
understandable B= Total number of
in the product functions (or types of
description? functions)
2. Demonstration What proportion A= Number of functions
capability of implemented with
functions demonstration capability
requiring B= Total number of
demonstration functions requiring
have such demonstration capability
capability?
3. Completeness What proportion A= Number of functions Usability/
of user of described correctly Learnability
documentation functions are B= Total of number of
and/or help correctly functions
facility described in the Implemented
user
documentation
and/or help
facility?
4. Operational How consistently A = number of Usability/ Operability
consistency can similar operations that behave
operations be inconsistently
carried out ? B= total number of
operations that behave
similarly
5. Message clarity How easily can A = number of messages
messages from a that are understood
system be easily
understood ? B = total number of
implemented messages
6. Customizing How many A=Number of
possibility functions and implemented functions
operational which can be customised
procedures during operation
can a user B=Number of functions
customize for his requiring the
convenience? customization capability
7. Input validity What proportion A = Number of input Usability/ User error
checking of input items items checked for valid protection
provide checking data
for valid data. B = Number of input
items which need
checking for valid data
8. Avoidance of How many A = number of functions
incorrect functions have implemented to
operation incorrect avoid critical or serious
operation malfunctions being
avoidance caused by incorrect
capability. operation
B = total number of
incorrect operation
patterns
9. Appearance What proportion A=Number of types of Usability/
customizability of user interface interface elements that User interface
of user elements can be can be customised. aesthetics measures
interface customised in B=Total number of types
appearance. of interface Elements
10. Physical What proportion A = number of functions Usability/
accessibility of accessible by the Accessibility
functions can a disabled person. measures
user with a B = total number of
physical functions implemented
handicap access
11. Access How controllable A= Number of detected Security/
controllability is the accesses to different types of Confidentiality
the system? illegal operations
B= Number of types of
illegal operations in
the specification
12. Data encryption How correctly is A = number of data
the items correctly
encryption/decry encrypted/decrypted
ption of data B = number of data items
items to be required
implemented encryption/decryption
as stated in the
requirement
spec.
13. Data corruption To what extent A = number of data Security/ Integrity
prevention can the data corruption instances
corruption be actually occurring
prevented? B = number of accesses
where data
damage or breakage is
expected to occur.
14. Utilization of What proportion A = number of events Security/ Non-
digital of events processed using repudiation
signature requiring non- digital signature
repudiation B = number of events
are processed requiring nonrepudiation
using property.
digital signature?
15. Access How complete is A = number of accesses Security/
auditability the audit trail to system and data Accountability
concerning the recorded in the system
user log
access to the B = number of accesses
system and actually occurred
data?
16. Authentication How well does A = number of provided Security/
methods the system authentication methods Authenticity
authenticate the (e.g., ID/password or IC
identity of card)
a subject or
resource?
Results of U&S metrics descriptions analysis gave us possibility to set up variants
of their interaction (table 4).
If we compare data from table 2 and 4 we can see, that sets of variants of
interaction of U&S subcharacteristics and their metrics do not identical, but very
similar. Some interactions were changed in the subcharacteristics context. In table 4
such changes were marked be the grey background. Such result is obvious, because
U&S metrics interact with subcharacteristics
Table 4. Variants of interaction metrics of U&S subcharacteristics.
2.1 2.2 2.3 2.4 2.5
Usability metrics (sub-
subcharacteristics)/
Authentication methods
Access controllability
Security metrics(sub-
Utilization of digital
Access auditability
subcharacteristics)
Data encryption
Data corruption
prevention
signature
1.1 Description
↑↑/↓↓ ? ? ? ? ?
completeness
Demonstration
↑↑/↓↓ ? ? ? ? ?
capability
1.2 Completeness
of user
documentation ↑↓ - - - - -
and/or help
facility
1.3 Operational
↑↑/↓↓ ? ↑↑/↓↓ ↑↑/↓↓ ↑↑/↓↓ ↑↑/↓↓
consistency
Message clarity ↑↑/↓↓ ? ↑↑/↓↓ ↑↑/↓↓ ↑↑/↓↓ ↑↑/↓↓
Customizing
↑↑/↓↓ ? ↑↑/↓↓ ↑↑/↓↓ ↑↑/↓↓ ↑↑/↓↓
possibility
1.4 Input validity
↑↑/↓↓ ? ↑↑/↓↓ ↑↑/↓↓ ↑↑/↓↓ ↑↑/↓↓
checking
Avoidance of
incorrect ↑↑/↓↓ ? ↑↑/↓↓ ↑↑/↓↓ ↑↑/↓↓ ↑↑/↓↓
operation
1.5 Appearance
customizability
↑↑/↓↓ ? ? ? ? ?
of user
interface
1.6 Physical
↑↓ ? ↑↓ ↑↓ ↑↓ ↑↓
accessibility
1. Usability subcharacteristics: 2. Security subcharacteristics
1.1 Appropriateness 2.1 Confidentiality
recognizability 2.2 Integrity
1.2 Learnability 2.3 Non-repudiation
1.3 Operability 2.4 Accountability
1.4 User error protection 2.5 Authenticity
1.5 User interface aesthetics
1.6 Accessibility
.
3 Case Study
We will represent simple example of U&S interaction. First of all, worth noting, that
metrics U&S equal to subsubcharacteristics (i.e. U&S subcharacteristics of second
level). In this case, with usage of calculated significances, from U&S metrics, in
author’s opinion, it is possible to do quantitative analysis of U&S interaction. We will
do such analysis for separate subcharacteristics of U&S characteristics. For example,
we will consider interaction of Operability and Confidentiality subcharacteristics on
basis of such interaction with metrics. For that see table. 3, which includes the
description of metrics and required primitives for calculation. Object of our research
will be web-site of Banking University (http://ubs.edu.ua/en/), which is on the stage
of the development. We will calculate metrics of significances for web-site before
making changes in this web-site (i.e. before testing). Results of calculation
represented in table. 5.
Table 5. Metrics significances.
Subcharacteristics/metrics 1 2
Operability Operational consistency
0,3 0,1
Message clarity 0,8 1
Customizing possibility 0,6 0,8
Confidentiality Access controllability 0,6 0,8
1. Metrics significances before make changes ( i.e. before testing);
2. Metrics significances after make changes.
For calculation of single significance for Operability subcharacteristic use additive
convolution, in which weighting coefficients for significances of metrics will be
equal. In result of calculation, we give following significances:
before making changes
Operabilitybefore = 0,3*0,33+0,8*0,33+0,6*0,33=0,099+0,264+0,198=0,561;
after making changes
Operabilityafter = 0,1*0,33+1*0,33+0,8*0,33=0,033+0,33+0,264=0,627.
Further, we will compare received significances for Operability and Confidentiality
subcharacteristics:
before making changes Operability= 0,561, а Confidentiality=0,6;
after making changes Operability= 0,627, а Confidentiality=0,8.
In result, we received significances for Operability and Confidentiality
subcharacteristics. Such significances increased after making changes in web-site in
comparison with before making changes. For Operability the difference equals 0,066
and for Confidentiality - 0,2. Thus, we have confirmation of our supposition about
interaction of Operability and Confidentiality characteristics, when increase of level
of one subcharacteristic incurring to increase in the level of other subcharacteristic
(table 2).
4 Conclusions
We have considered two basic aspects of U&S interaction: usable security and secure
usability. Differences in such aspects were analyzed by use of practical examples.
This work includes results of analysis of U&S interaction on the level of
subcharacteristics and metrics. Results of such research give possibility to define the
set of variants of the interaction of U&S subcharacteristics and metrics. Such variants
of interaction of subcharacteristics and metrics are not identical, but are very similar.
In future authors are planning to make complete quantitative analysis of interaction
of U&S subcharacteristics on the base of calculated metrics values. Authors suppose,
that such analysis must confirm that variants of interaction of U&S subcharacteristics
assessment will be correct. Also we plan to analyze interaction between U&S
characteristics of information systems and another once, for example, safety.
Practical results of such assessment are improving of requirements foundation for
U&S and other characteristics and correcting of design decisions.
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18. ISO/IEC 25030: Software engineering – Software product Quality Requirements and
Evaluation (SQuaRE) – Quality requirements, ISO/IEC (2007)
19. Usability of security team at National institute of standards and Technology
(http://csrc.nist.gov/security-usability/HTML/about.html).
20. Completely Automated Public Turing test to tell Computers and Humans Apart,
CAPCHA (http://www.captcha.net/).