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Файл:Information protection in digital communication systems. Textbook
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211
When planning restoration work, you should be aware that it is not
always possible to fully maintain the functioning of the organization. It is
necessary to identify critical functions, without which the organization loses
its face, and even prioritize among critical functions in order to resume work
after an accident as quickly as possible and at minimal cost.
When identifying the resources needed to perform critical functions,
remember that many of them are non-computer in nature. At this stage, it is
advisable to involve specialists of various profiles in the work, who are
capable of collectively covering all aspects of the problem. Critical
resources typically fall into one of the following categories:
• staff;
• information infrastructure;
• physical infrastructure.
When compiling lists of responsible specialists, it should be taken into
account that some of them may be directly affected by an accident (for
example, a fire), someone may be under stress, some employees may be
unable to get to work (for example, in the event of mass unrest). It is
advisable to have some reserve of specialists or to determine in advance the
channels through which additional personnel can be temporarily recruited.
The information infrastructure includes the elements described in the
“asset identification” paragraph.
You need to prepare for the fact that at the “alternate airfield” where
the organization will be evacuated after an accident, the hardware platform
may differ from the original one. Accordingly, measures to maintain
program and data compatibility should be considered.
Among external information services for commercial organizations, it
is probably most important to obtain operational information and
communication with government services that oversee this sector of the
economy.
Documentation is important, if only because not all information that
an organization works with is presented in electronic form. Most likely, the
restoration plan is printed on paper.
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Physical infrastructure includes buildings, utilities, communications,
office equipment and much more. Computer equipment cannot work in poor
conditions, without a stable power supply, etc.
When analyzing critical resources, it is advisable to take into account
the time profile of their use. Most resources are required on an ongoing
basis, but some may only be needed at certain times (for example, at the end
of a month or year when generating a report).
When determining the list of possible accidents, you need to try to
develop their scenarios. How will events develop? What is the scale of the
disaster? What will happen to critical resources? For example, will employees
be able to get to work? Will computers be disabled? Are cases of sabotage
possible? Will the connection work? Will the organization’s building be
damaged? Will it be possible to find and read the necessary papers?
The recovery strategy should be based on available resources and not
be too expensive for the organization. When developing a strategy, it is
advisable to analyze the risks to which critical functions are exposed and try
to select the most cost-effective solution.
The strategy should include not only work under a temporary scheme,
but also a return to normal functioning.
Preparing for the implementation of the chosen strategy consists of
developing a plan of action in emergency situations and after them, as well
as ensuring some redundancy of critical resources. The latter is possible
without a large expenditure of funds if you conclude agreements with one
or more organizations on mutual support in the event of accidents — those
who were not injured provide part of their resources for temporary use to
less fortunate partners.
Redundancy is also ensured by backup measures, storing copies in
multiple places, presenting information in different forms (on paper and in
files), etc. It makes sense to enter into an agreement with information service
providers for priority service in critical situations or enter into agreements
with multiple providers. However, these measures may require certain costs.
The strategy is checked by analyzing the prepared plan, measures
taken and planned.
213
6.4. SOFTWARE AND TECHNICAL LEVEL
In the previous sections on practical measures for building an
integrated enterprise information security system, the legislative,
administrative and procedural levels of the IS system were covered. The last
level of formation of a secure information system is responsible for the
development of software and hardware measures and, accordingly, is called
the software and hardware level.
Work at this level consists of selecting mechanisms (subsystems) and
IS tools (Fig. 6.3).
Основные механизмы
Идентификация и аутентификация
Разграничение доступа
Регистрация и аудит
Криптография
Экранирование
Основные средства
Средства контроля доступа
Средства шифрования информации
Средства антивирусной защиты
Средства межсетевого экранирования
Средства гарантированного хранения
Средства защиты от сбоев электропитания
и защиты кабельной системы
Инструментальные средства
администратора безопасности
Fig. 6.3. Basic mechanisms and means of an integrated
enterprise information security system
Next, we will consider the mechanisms and means presented in more
detail.
6.4.1. Identification and Authentication
The basis of IS systems is identification and authentication, since all
information security mechanisms are designed to work with named AS
subjects and objects. AS subjects can be both users and processes, and AS
objects can be information and other information resources of the system.
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Assigning a personal identifier to subjects and access objects and
comparing it with a given list is called identification. User ID is a certain
unique amount of information that allows you to distinguish between
individual users of a password system (identify them). Often the identifier
is also called the username or user account name. Identification ensures the
performance of the following IS functions [3]:
1) establishing the authenticity and determining the powers of the
subject upon his admission to the system;
2) control of established powers during a work session;
3) registration of actions, etc.
Authentication is the verification of the access subject’s ownership
of the identifier presented by him and confirmation of its authenticity. In
other words, authentication consists of checking whether the connecting
subject is who he claims to be [3].
Authentication procedure. The general procedure for identifying and
authenticating a user when accessing the AS is presented in Fig. 6.4. If the
authentication of the subject is established during the authentication process,
then the information security system must determine his powers (set of
rights). This is necessary for subsequent control and differentiation of access
to resources
Уведомление пользователя об ошибке
Допустимое
число попыток?
Сигнализация об НСД,
временная блокировка
Нет
Ввод идентификатора пользователя
Правильный
идентификатор?
Уведомление пользователя
о входе в систему
Вызов процедуры аутентификации
Идентифицирован
пользователь?
Нет
Нет
Да
Fig. 6.4. Classic identification and authentication procedure
215
Classification of authentication systems. Authentication systems can
be classified according to various criteria (Fig. 6.5).
Аутентификация
По контролируемым
компонентам
По направленности
По используемым
средствам
По уровню
информационной
безопасности
Аутентификация
партнеров
Аутентификация
источника
данных
Односторонняя
Двухсторонняя
Пароль
Биометрические
параметры
Уникальный
предмет
Информация,
ассоциированная
с пользователем
Статическая
Устойчивая
Постоянная
Fig. 6.5. Classification of authentication systems
Based on the controlled component of the system, authentication
methods can be divided into authentication of communication partners and
authentication of the data source. Authentication of communication partners
is used when establishing (and periodically checking) a connection during a
session. It serves to prevent threats such as masquerade and replay of the
previous communication session. Data source authentication is confirmation
of the authenticity of the source of a single piece of data.
In terms of direction, authentication can be one-way (the user proves
his authenticity to the system, for example, when logging into the system)
and two-way (mutual).
Typically, authentication methods are classified according to the
means used. In this case, these methods are divided into four groups:
• based on knowledge by a person entitled to access system resources
of some secret information — a password;
• based on the use of a unique item: token, electronic card, etc.;
• based on the measurement of human biometric parameters —
physiological or behavioral attributes of a living organism;
216
• based on information associated with the user, for example, his
coordinates.
Let’s take a closer look at these groups.
1. The most common, simple and familiar are authentication methods
based on passwords — secret identifiers of subjects. Here, when the subject
enters his password, the authentication subsystem compares it with the
password stored in encrypted form in the reference database. If the
passwords match, the authentication subsystem allows access to AS
resources.
Password methods should be classified according to the degree to
which passwords can be changed:
• methods using permanent (reusable) passwords;
• methods using one-time (dynamically changing) passwords.
Most AS use reusable passwords. In this case, the user’s password
does not change from session to session during the validity period set by the
system administrator. This simplifies administration procedures, but
increases the risk of password compromise. There are many known ways to
reveal a password: from peeking over your shoulder to intercepting a
communication session. The likelihood of an attacker opening a password
increases if the password has a semantic meaning (year of birth, girl’s
name), is short in length, typed in one register, has no restrictions on the
period of existence, etc. It is important whether the password is allowed to
be entered only in interactive mode or the ability to access from the program.
In the latter case, it is possible to run a password guessing program. A more
secure way is to use one-time or dynamically changing passwords. The
following password protection methods based on one-time passwords are
known:
• methods for modifying the simple password scheme;
• request-response methods;
• functional methods.
In the first case, the user is given a list of passwords. During
authentication, the system asks the user for a password, the number in the
217
list of which is determined by a random law. The length and sequence
number of the initial character of the password can also be set randomly.
When using the challenge-response method, the system asks the user
some general questions, the correct answers to which are known only to a
specific user.
Functional methods are based on the use of a special password
conversion function F(X). This makes it possible to change (according to
some formula) user passwords over time. The specified function must
satisfy the following requirements:
1) for a given password X it is easy to calculate a new password Y =
F(X);
2) knowing X and Y, it is difficult or impossible to determine the
function F(X).
The most famous examples of functional methods are the functional
transformation method and the handshake method.
The idea of the functional transformation method is to periodically
change the function F(X) itself. The latter is achieved by the presence in the
functional expression of dynamically changing parameters, for example, a
function of a certain date and time. The user is informed of the original
password, the function itself, and the frequency of changing the password.
It is easy to see that the user’s passwords for given n-periods of time will be
the following: X, F(X), F(F(X)), ... F(X)
n–1
.
The handshake method is as follows. The password conversion
function is known only to the user and the security system. When entering
the AS, the authentication subsystem generates a random sequence X, which
is transmitted to the user. The user calculates the result of the function Y=
F(X) and returns it to the system. The system compares its own calculated
result with that received from the user. If the specified results match, the
user’s authenticity is considered proven.
The advantage of the method is that the transmission of any
information that could be used by an attacker is minimized.
In some cases, the user may need to verify the authenticity of another
remote user or some AS that he is about to access. The most suitable method
218
here is the “handshake” method, since none of the participants in the
information exchange will receive any confidential information.
Note that authentication methods based on one-time passwords also
do not provide absolute protection. For example, if an attacker has the ability
to connect to a network and intercept transmitted packets, then he can send
the latter as his own.
2. Recently, combined identification methods have become widespread,
requiring, in addition to knowing the password, the presence of a card
(token) — a special device that confirms the authenticity of the subject.
Cards are divided into two types:
• passive (memory cards);
• active (smart cards).
The most common are passive cards with a magnetic stripe, which are
read by a special device that has a keyboard and a processor. When using
the specified card, the user enters his identification number. If it matches the
electronic version encoded in the card, the user gains access to the system.
This allows you to reliably identify the person who gained access to the
system and prevent unauthorized use of the card by an attacker (for example,
if it is lost). This method is often called two-factor authentication.
Sometimes (usually for physical access control) cards are used on their
own, without requiring a personal identification number.
The advantage of using cards is that the processing of authentication
information is performed by the reader, without being transferred to the
computer memory. This eliminates the possibility of electronic interception
via communication channels.
The disadvantages of passive cards are the following: they are
significantly more expensive than passwords, they require special reading
devices, and their use requires special procedures for secure accounting and
distribution. They also need to be protected from intruders; first of all, of
course, they should not be left in the devices. There are known cases of
counterfeiting of passive cards.
In addition to memory, smart cards have their own microprocessor.
This allows you to implement various options for password protection
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methods, such as: reusable passwords, dynamically changing passwords,
usually “challenge-response” methods. All cards provide two-component
authentication.
To these advantages of smart cards we should add their versatility.
They can be used not only for security purposes, but also, for example, for
financial transactions. A concomitant disadvantage of cards is their high
cost.
3. Authentication methods based on measuring human biometric
parameters provide almost 100 % identification, solving the problems of
lost passwords and personal identifiers. However, the methods cannot be
used to identify processes or data (data objects), they are just beginning to
develop (there are problems with standardization and dissemination), and
they still require complex and expensive equipment. This determines their
use so far only at particularly important facilities and systems, mainly in the
Russian Defense Ministry.
Examples of the implementation of these methods are user
identification systems based on the pattern of the iris, palm prints, ear
shapes, infrared patterns of capillary vessels, handwriting, smell, voice
timbre, and even DNA (Fig. 6.6).
Физиологические методы
Снятие отпечатков пальцев
Сканирование радужной оболочки глаза
Сканирование сетчатки глаза
Геометрия кисти руки
Распознавание черт лица
Поведенческие методы
Анализ подписи
Анализ тембра голоса
Анализ почерка
Методы биометрии
Fig. 6.6. Examples of common biometric methods
A new direction is the use of biometric characteristics in smart
payment cards, pass tokens and cellular communication elements. For
220
example, when paying in a store, the cardholder puts his finger on the
scanner to confirm that the card is really his.
Let’s name the most used biometric attributes and the corresponding
systems.
Fingerprints. Such scanners are small in size, universal, and relatively
inexpensive. The biological repeatability of a fingerprint is 10–5 %.
Currently being promoted by law enforcement agencies due to large
allocations to electronic fingerprint archives.
Hand geometry. Appropriate devices are used when finger scanners
are difficult to use due to dirt or injury. The biological repeatability of hand
geometry is about 2 %.
Iris. These devices have the highest accuracy. The theoretical
probability of two irises matching is 1 in 1078.
Thermal image of the face. The systems make it possible to identify a
person at a distance of up to tens of meters. In combination with database
searching, such systems are used to identify authorized employees and
screen out unauthorized personnel. However, face scanners have a relatively
high error rate when lighting changes.
Voice. Voice verification is convenient for use in telecommunications
applications. The required 16-bit sound card and condenser microphone cost
less than $25. The error rate is 2–5 %. This technology is suitable for voice
verification over telephone communication channels; it is more reliable
compared to frequency dialing of a personal number. Nowadays, directions
are being developed for identifying a person and his state by voice —
excited, sick, telling the truth, crazy, etc.
Keyboard input. Here, when entering, for example, a password, the
speed and intervals between keystrokes are monitored.
Signature. Digitizers are used to control handwritten signatures.
4. The newest direction in authentication is to prove the authenticity
of a remote user by his location. This protective mechanism is based on the
use of a space navigation system such as GPS (Global Positioning System).
A user with GPS equipment repeatedly sends the coordinates of specified
satellites located in the line of sight. The authentication subsystem, knowing
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