Security and Privacy

© Ian Sommerville 2018

 Software security

• Software security should always be a high priority for product developers

and their users.

• If you don’t prioritize security, you and your customers will inevitably
suffer losses from malicious attacks.

• In the worst case, these attacks could can put product providers out of
business.

• If their product is unavailable or if customer data is compromised, customers are

liable to cancel their subscriptions.

• Even if they can recover from the attacks, this will take time and effort
that would have been better spent working on their software.

Security and Privacy © Ian Sommerville 2018: 2

 Figure 7.1 Types of security threat
Figure 7.1 Types of security threat

An attacker attempts An attacker attempts

to deny access to the system to damage the system
for legitimate users or its data.

Availability Integrity
threats threats

SOFTWARE PRODUCT

PROGRAM
Example: Virus
Example: Distributed denial
of service attack DATA

Example: Ransomware

Example: Data theft

Confidentiality
threats

An attacker tries to gain

access to private information
held by the system

Security and Privacy © Ian Sommerville 2018: 3

 Figure 7.2 System infrastructure stack infrastructure stack
Figure 7.2 System

Operational environment

Application

Frameworks and application libraries

Browsers and messaging

System libraries

Database

Operating system

Software infrastructure

Network

Security and Privacy © Ian Sommerville 2018: 4

 Table 7.1 Security management

Authentication and authorization

You should have authentication and authorization standards and procedures that
ensure that all users have strong authentication and that they have properly access
permissions properly. This minimizes the risk of unauthorized users accessing system
resources.

System infrastructure management

Infrastructure software should be properly configured and security updates that patch
vulnerabilities should be applied as soon as they become available.

Attack monitoring
The system should be regularly checked for possible unauthorized access. If attacks
are detected, it may be possible to put resistance strategies in place that minimize the
effects of the attack.

Backup
Backup policies should be implemented to ensure that you keep undamaged copies of
program and data files. These can then be restored after an attack.

Security and Privacy © Ian Sommerville 2018: 5

 Operational security

• Operational security focuses on helping users to maintain security. User

attacks try to trick users into disclosing their credentials or accessing a
website that includes malware such as a key-logging system.

• Operational security procedures and practices

• Auto-logout, which addresses the common problem of users forgetting to logout

from a computer used in a shared space.

• User command logging, which makes it possible to discover actions taken by

users that have deliberately or accidentally damaged some system resources.

• Multi-factor authentication, which reduces the chances of an intruder gaining

access to the system using stolen credentials.

Security and Privacy © Ian Sommerville 2018: 6

 Injection attacks

• Injection attacks are a type of attack where a malicious user uses a valid
input field to input malicious code or database commands.

• These malicious instructions are then executed, causing some damage

to the system. Code can be injected that leaks system data to the
attackers.

• Common types of injection attack include buffer overflow attacks and

SQL poisoning attacks.

Security and Privacy © Ian Sommerville 2018: 7

 SQL poisoning attacks

• SQL poisoning attacks are attacks on software products that use an SQL
database.

• They take advantage of a situation where a user input is used as part of

an SQL command.

• A malicious user uses a form input field to input a fragment of SQL that
allows access to the database.

• The form field is added to the SQL query, which is executed and returns
the information to the attacker.

Security and Privacy © Ian Sommerville 2018: 8

 Cross-site scripting attacks

• Cross-site scripting attacks are another form of injection attack.

• An attacker adds malicious Javascript code to the web page that is

returned from a server to a client and this script is executed when the
page is displayed in the user’s browser.

• The malicious script may steal customer information or direct them to

another website.

• This may try to capture personal data or display advertisements.

• Cookies may be stolen, which makes a session hijacking attack possible.

• As with other types of injection attack, cross-site scripting attacks may be

avoided by input validation.

Security and Privacy © Ian Sommerville 2018: 9

 Figure 7.3 Cross-site scripting attack

Figure 7.3 Cross-site scripting attack

1. Product website
Attacker Introduce
malicious code
Browser Malicious code
added to valid data
Website

3.
Malware script
sends session cookie
to attacker
Valid request for data
from website
Browser

2.
Victim Data delivered and malware
script installed in victim’s browser

Security and Privacy © Ian Sommerville 2018: 10

 Session hijacking attacks

• When a user authenticates themselves with a web application, a session is

created.

• A session is a time period during which the user’s authentication is valid. They don’t
have to re-authenticate for each interaction with the system.

• The authentication process involves placing a session cookie on the user’s device

• Session hijacking is a type of attack where an attacker gets hold of a session

cookie and uses this to impersonate a legitimate user.

• There are several ways that an attacker can find out the session cookie
value including cross-site scripting attacks and traffic monitoring.

• In a cross-site scripting attack, the installed malware sends session cookies to the
attackers.

• Traffic monitoring involves attackers capturing the traffic between the client and
server. The session cookie can then be identified by analysing the data exchanged.

Security and Privacy © Ian Sommerville 2018: 11

 Table 7.2 Actions to reduce the likelihood of hacking

Traffic encryption
Always encrypt the network traffic between clients and your server. This means
setting up sessions using https rather than http. If traffic is encrypted it is harder
to monitor to find session cookies.

Multi-factor authentication
Always use multi-factor authentication and require confirmation of new actions
that may be damaging. For example, before a new payee request is accepted,
you could ask the user to confirm their identity by inputting a code sent to their
phone. You could also ask for password characters to be input before every
potentially damaging action, such as transferring funds.

Short timeouts
Use relatively short timeouts on sessions. If there has been no activity in a
session for a few minutes, the session should be ended and future requests
directed to an authentication page. This reduces the likelihood that an attacker
can access an account if a legitimate user forgets to log off when they have
finished their transactions.

Security and Privacy © Ian Sommerville 2018: 12

 Denial of service attacks

• Denial of service attacks are attacks on a software system that are intended to make
that system unavailable for normal use.

• Distributed denial of service attacks (DDOS) are the most common type of denial of
service attacks.

• These involve distributed computers, that have usually been hijacked as part of a botnet,
sending hundreds of thousands of requests for service to a web application. There are so
many service requests that legitimate users are denied access.

• Other types of denial of service attacks target application users.

• User lockout attacks take advantage of a common authentication policy that locks out a user
after a number of failed authentication attempts. Their aim is to lock users out rather than gain
access and so deny the service to these users.

• Users often use their email address as their login name so if an attacker has access to a
database of email addresses, he or she can try to login using these addresses.

• If you don’t lock accounts after failed validation, then attackers can use brute-force
attacks on your system. If you do, you may deny access to legitimate users.

Security and Privacy © Ian Sommerville 2018: 13

 Brute force attacks

• Brute force attacks are attacks on a web application where the attacker
has some information, such as a valid login name, but does not have the
password for the site.

• The attacker creates different passwords and tries to login with each of
these. If the login fails, they then try again with a different password.

• Attackers may use a string generator that generates every possible combination
of letters and numbers and use these as passwords.

• To speed up the process of password discovery, attackers take advantage of the

fact that many users choose easy-to-remember passwords. They start by trying
passwords from the published lists of the most common passwords.

• Brute force attacks rely on users setting weak passwords, so you can
circumvent them by insisting that users set long passwords that are not
in a dictionary or are common words.

Security and Privacy © Ian Sommerville 2018: 14

 Authentication

• Authentication is the process of ensuring that a user of your system is

who they claim to be.

• You need authentication in all software products that maintain user

information, so that only the providers of that information can access and
change it.

• You also use authentication to learn about your users so that you can
personalize their experience of using your product.

Security and Privacy © Ian Sommerville 2018: 15

 Figure 7.4 Authentication approaches
Figure 7.4 Authentication approaches

Authentication approach Example

Knowledge Password

Possession Mobile
device

Authenticating user Attribute Fingerprint

Security and Privacy © Ian Sommerville 2018: 16

 Authentication methods

• Knowledge-based authentication

• The user provides secret, personal information when they register with the
system. Each time they log on, the system asks them for this information.

• Possession-based authentication

• This relies on the user having a physical device (such as a mobile phone) that
can generate or display information that is known to the authenticating system.
The user inputs this information to confirm that they possess the authenticating
device.

• Attribute-based authentication is based on a unique biometric attribute of

the user, such as a fingerprint, which is registered with the system.

• Multi-factor authentication combines these approaches and requires

users to use more than one authentication method.

Security and Privacy © Ian Sommerville 2018: 17

 Table 7.3 Weaknesses of password-password-based authentication

Insecure passwords
Users choose passwords that are easy to remember. However, it is also easy for
attackers to guess or generate these passwords, using either a dictionary or a
brute force attack.

Phishing attacks
Users click on an email link that points to a fake site that tries to collect their login
and password details.

Password reuse
Users use the same password for several sites. If there is a security breach at
one of these sites, attackers then have passwords that they can try on other
sites.

Forgotten passwords
Users regularly forget their passwords so that you need to set up a password
recovery mechanism to allow these to be reset. This can be a vulnerability if
users’ credentials have been stolen and attackers use it to reset their passwords.

Security and Privacy © Ian Sommerville 2018: 18

 Federated identity

• Federated identity is an approach to authentication where you use an

external authentication service.

• ‘Login with Google’ and ‘Login with Facebook’ are widely used examples
of authentication using federated identity.

• The advantage of federated identity for a user is that they have a single
set of credentials that are stored by a trusted identity service.

• Instead of logging into a service directly, a user provides their credentials

to a known service who confirms their identity to the authenticating
service.

• They don’t have to keep track of different user ids and passwords.
Because their credentials are stored in fewer places, the chances of a
security breach where these are revealed is reduced.

Security and Privacy © Ian Sommerville 2018: 19

 Figure 7.5 Federated identity
Figure 7.5 Federated identity

User Service Trusted authenticator

Request
authentication
Divert request

Request credentials

Provide credentials

Return authentication
token
Authentication
response

Security and Privacy © Ian Sommerville 2018: 20

 Authorization

• Authentication involves a user proving their identity to a software system.

• Authorization is a complementary process in which that identity is used

to control access to software system resources.

• For example, if you use a shared folder on Dropbox, the folder’s owner may
authorize you to read the contents of that folder, but not to add new files or
overwrite files in the folder.

• When a business wants to define the type of access that users get to
resources, this is based on an access control policy.

• This policy is a set of rules that define what information (data and
programs) is controlled, who has access to that information and the type
of access that is allowed

Security and Privacy © Ian Sommerville 2018: 21

 Access control policies

• Explicit access control policies are important for both legal and technical
reasons.

• Data protection rules limit the access the personal data and this must be
reflected in the defined access control policy. If this policy is incomplete or does
not conform to the data protection rules, then there may be subsequent legal
action in the event of a data breach.

• Technically, an access control policy can be a starting point for setting up the
access control scheme for a system.

• For example, if the access control policy defines the access rights of students,
then when new students are registered, they all get these rights by default.

Security and Privacy © Ian Sommerville 2018: 22

 Access control lists

• Access control lists (ACLs) are used in most file and database systems
to implement access control policies.

• Access control lists are tables that link users with resources and specify
what those users are permitted to do.

• For example, for this book I would like to be able to set up an access control list
to a book file that allows reviewers to read that file and annotate it with
comments. However, they are not allowed to edit the text or to delete the file.

• If access control lists are based on individual permissions, then these

can become very large. However, you can dramatically cut their size by
allocating users to groups and then assigning permissions to the group

Security and Privacy © Ian Sommerville 2018: 23

 Figure 7.8 Access control lists
Figure 7.8 Access control lists

User Permissions
All Read
Staff Create, Edit
Resource Access
Sysadmin Delete
A

B User Permissions
All Execute
C
Sysadmin Create, Delete
D

User Permissions
...
Admin Create, Read, Edit
Teaching staff Read, Edit
Student Read

if student = student_id

if department = dept_id

Security and Privacy © Ian Sommerville 2018: 24

 Encryption

• Encryption is the process of making a document unreadable by applying

an algorithmic transformation to it.

• A secret key is used by the encryption algorithm as the basis of this

transformation. You can decode the encrypted text by applying the
reverse transformation.

• Modern encryption techniques are such that you can encrypt data so that
it is practically uncrackable using currently available technology.

• However, history has demonstrated that apparently strong encryption

may be crackable when new technology becomes available.

• If commercial quantum systems become available, we will have to use a

completely different approach to encryption on the Internet.

Security and Privacy © Ian Sommerville 2018: 25

 Figure 7.9 Encryption and decryption

Figure 7.9 Encryption and decryption

Secret Secret
key key

Plain Encrypted Plain

Encrypt Decrypt
text text text

Security and Privacy © Ian Sommerville 2018: 26

 Symmetric encryption

• In a symmetric encryption scheme, the same encryption key is used for

encoding and decoding the information that is to be kept secret.

• If Alice and Bob wish to exchange a secret message, both must have a
copy of the encryption key. Alice encrypts the message with this key.
When Bob receives the message, he decodes it using the same key to
read its contents.

• The fundamental problem with a symmetric encryption scheme is

securely sharing the encryption key.

• If Alice simply sends the key to Bob, an attacker may intercept the
message and gain access to the key. The attacker can then decode all
future secret communications.

Security and Privacy © Ian Sommerville 2018: 27

 Figure 7.10 Symmetric encryption
Figure 7.10 Symmetric encryption

Alice Bob

Encryption key Encryption key

a7Dr6yYt9F... a7Dr6yYt9F...

encrypt decrypt

Secret message Encrypted text Secret message

Security and Privacy © Ian Sommerville 2018: 28

 Asymmetric encryption

• Asymmetric encryption, does not require secret keys to be shared.

• An asymmetric encryption scheme uses different keys for encrypting and

decrypting messages.

• Each user has a public and a private key. Messages may be encrypted
using either key but can only be decrypted using the other key.

• Public keys may be published and shared by the key owner. Anyone can
access and use a published public key.

• However, messages can only be decrypted by the user’s private key so

is only readable by the intended recipient

Security and Privacy © Ian Sommerville 2018: 29

 Figure
Figure 7.11 Asymmetric
7.11 Asymmetric encryption
encryption

Alice Bob

Bob’s public key Bob’s private key

dr5ts3TR9dt hTr34BbfsDy
x4ztmRsYY... 9r3g5HHt76...

encrypt decrypt

Secret message Encrypted text Secret message

Security and Privacy © Ian Sommerville 2018: 30

 Encryption and authentication

• Asymmetric encryption can also be used to authenticate the sender of a

message by encrypting it with a private key and decrypting it with the
corresponding public key.

• Say Alice wants to send a message to Bob and she has a copy of his
public key.

• However, she is not sure whether or not the public key that she has for
Bob is correct and she is concerned that the message may be sent to the
wrong person.

• Private/public key encryption can be used to verify Bob’s identity.

• Bob uses his private key to encrypt a message and sends this to Alice. If it can
be decrypted using Bob’s public key, then Alice has the correct key.

Security and Privacy © Ian Sommerville 2018: 31

 Figure 7.12 Encryption for authentication
Figure 7.12 Encryption for authentication

Bob Alice

Bob’s private key Bob’s public key

hTr34BbfsDy dr5ts3TR9dt
9r3g5HHt76... x4ztmRsYY...

encrypt decrypt

I am really I am really
Encrypted text
Bob Bob

Security and Privacy © Ian Sommerville 2018: 32

 TLS and digital certificates

• The https protocol is a standard protocol for securely exchanging texts on

the web. It is the standard http protocol plus an encryption layer called TLS
(Transport Layer Security). This encryption layer is used for 2 things:

• to verify the identity of the web server;

• to encrypt communications so that they cannot be read by an attacker who

intercepts the messages between the client and the server

• TLS encryption depends on a digital certificate that is sent from the web
server to the client.

• Digital certificates are issued by a certificate authority (CA), which is a trusted

identity verification service.

• The CA encrypts the information in the certificate using their private key to create a
unique signature. This signature is included in the certificate along with the public
key of the CA. To check that the certificate is valid, you can decrypt the signature
using the CA’s public key.

Security and Privacy © Ian Sommerville 2018: 33

 Table 7.5 Digital certificates

Subject information
Information about the company or individual whose web site is being visited. Applicants
apply for a digital certificate from a certificate authority who checks that the applicant is a
valid organization.

Certificate authority information

Information about the certificate authority (CA) who has issued the certificate.

Certificate information
Information about the certificate itself, including a unique serial number and a validity
period, defined by start and end dates.

Digital signature
The combination of all of the above data uniquely identifies the digital certificate. The
signature data is encrypted with the CA’s private key to confirm that the data is correct. The
algorithm used to generate the digital signature is also specified.

Public key information

The public key of the CA is included along with the key size and the encryption algorithm
used. The public key may be used to decrypt the digital signature.

Security and Privacy © Ian Sommerville 2018: 34

 Figure 7.13 Using symmetric and asymmetric encryption in TLS
Figure 7.13 Using symmetric and asymmetric encryption in TLS
CLIENT SERVER
Encryption methods
supported
Hello

Encryption method to be used

Hello

Prove your identity?

Verify

Generate RS is a large
RS random number

Encrypt Encrypt RS using

RS private key

Digital certificate + encrypted RS Get

Check certificate issuer certificate
and validity and digital Check
signature on certificate
RC is a large Generate
random number RC
Decrypt
Decrypt RS and encrypt RS
RC using public key
from digital certificate Encrypt Encrypted RC Decrypt Decrypt RC using
RC RC private key

Compute the Compute the

Compute Compute
symmetric key symmetric key
key key
using RS and RC using RS and RC
Data encrypted using
Exchange symmetric key Exchange
data data

End End
session session
Security and Privacy © Ian Sommerville 2018: 35
 TLS explained

• The digital certificate that the server sends to the client includes the
server’s public key. The server also generates a long random number,
encrypts it using its private key and sends this to the client.

• The client can then decrypt this using the server’s public key and, in turn,
generates its own long random number. It encrypts this number using the
server’s public key and sends it to the server, which decrypts the
message using its private key. Both client and server then have two long
random numbers.

• The agreed encryption method includes a way of generating an

encryption key from these numbers. The client and server independently
compute the key that will be used to encrypt subsequent messages using
a symmetric approach.

• All client-server traffic is encrypted and decrypted using that computed

key. There is no need to exchange the key itself.

Security and Privacy © Ian Sommerville 2018: 36

 Data encryption

• As a product provider you inevitably store information about your users and,
for cloud-based products, user data.

• Encryption can be used to reduce the damage that may occur from data
theft. If information is encrypted, it is impossible, or very expensive, for
thieves to access and use the unencrypted data.

• Data in transit.
When transferring the data over the Internet, you should always use the https rather
than the http protocol to ensure encryption.

• Data at rest.
If data is not being used, then the files where the data is stored should be encrypted
so that theft of these files will not lead to disclosure of confidential information.

• Data in use
The data is being actively processed. Encrypting and decrypting the data slows
down the system response time. Implementing a general search mechanism with
encrypted data is impossible,

Security and Privacy © Ian Sommerville 2018: 37

 Figure 7.14 Encryption levels
Figure 7.14 Encryption levels

The application decides what data should be

Application encrypted and decrypts that data immediately
before it is used.

The DMBS may encrypt the entire database

when it is closed, with the database decrypted
Database
when it is reopened. Alternatively individal tables
or columns may be encrypted/decrypted.

The operating system encrypts individual files

Files when they are closed and decrypts them when
they are reopened.

The operating system encrypts disks when they

Media are unmounted and decrypts these disks when
they are remounted.

Security and Privacy © Ian Sommerville 2018: 38

 Key management

• Key management is the process of ensuring that encryption keys are

securely generated, stored and accessed by authorized users.

• Businesses may have to manage tens of thousands of encryption keys

so it is impractical to do key management manually and you need to use
some kind of automated key management system (KMS).

• Key management is important because, if you get it wrong, unauthorized

users may be able to access your keys and so decrypt supposedly
private data. Even worse, if you lose encryption keys, then your
encrypted data may be permanently inaccessible.

• A key management system (KMS) is a specialized database that is

designed to securely store and manage encryption keys, digital
certificates and other confidential information.

Security and Privacy © Ian Sommerville 2018: 39

 Figure 7.15 Using a KMS for encryption management
Figure 7.15 Using a KMS for encryption management

Application

Calls
Unencrypted data

API

Key management
API Encryption
system engine
Keys

Key store Stored encrypted

data

Security and Privacy © Ian Sommerville 2018: 40

 Long-term key storage

• Business may be required by accounting and other regulations to keep

copies of all of their data for several years.

• For example, in the UK, tax and company data has to be maintained for at least
six years, with a longer retention period for some types of data. Data protection
regulations may require that this data be stored securely, so the data should be
encrypted.

• To reduce the risks of a security breach, encryption keys should be

changed regularly. This means that archival data may be encrypted with
a different key from the current data in your system.

• Therefore, key management systems must maintain multiple,

timestamped versions of keys so that system backups and archives can
be decrypted if required.

Security and Privacy © Ian Sommerville 2018: 41

 Privacy

• Privacy is a social concept that relates to the collection, dissemination

and appropriate use of personal information held by a third-party such as
a company or a hospital.

• The importance of privacy has changed over time and individuals have
their own views on what degree of privacy is important.

• Culture and age also affect peoples’ views on what privacy means.

• Younger people were early adopters of the first social networks and many of
them seem to be less inhibited about sharing personal information on these
platforms than older people.

• In some countries, the level of income earned by an individual is seen as a

private matter; in others, all tax returns are openly published.

Security and Privacy © Ian Sommerville 2018: 42

 Business reasons for privacy

• If you are offering a product directly to consumers and you fail to conform
to privacy regulations, then you may be subject to legal action by product
buyers or by a data regulator. If your conformance is weaker than the
protection offered by data protection regulations in some countries, you
won’t be able to sell your product in these countries.

• If your product is a business product, business customers require privacy

safeguards so that they are not put at risk of privacy violations and legal
action by users.

• If personal information is leaked or misused, even if this is not seen as a

violation of privacy regulations, this can lead to serious reputational
damage. Customers may stop using your product because of this

Security and Privacy © Ian Sommerville 2018: 43

 Data protection laws

• In many countries, the right to individual privacy is protected by data

protection laws.

• These laws limit the collection, dissemination and use of personal data to
the purposes for which it was collected.

• For example, a travel insurance company may collect health information so that
they can assess their level of risk. This is legal and permissible.

• However, it would not be legal for those companies to use this information to
target online advertising of health products, unless their users had given specific
permission for this.

Security and Privacy © Ian Sommerville 2018: 44

 Figure 7.16 Data protection laws

Figure 7.16 Data protection laws

Responsibilities of Rights of the

the data controller data subject

Data storage Data protection Data access

Data use laws Error correction
Security Data deletion
Subject access Consent

Security and Privacy © Ian Sommerville 2018: 45

 Table 7.6 Data protection principles (1)

Awareness and control

Users of your product must be made aware of what data is collected when they
are using your product, and must have control over the personal information that
you collect from them.

Purpose
You must tell users why data is being collected and you must not use that data
for other purposes.

Consent
You must always have the consent of a user before you disclose their data to
other people.

Data lifetime
You must not keep data for longer than you need to. If a user deletes their
account, you must delete the personal data associated with that account.

Security and Privacy © Ian Sommerville 2018: 46

 Data protection principles (2)

Secure storage
You must maintain data securely so that it cannot be tampered with or disclosed
to unauthorized people.

Discovery and error correction

You must allow users to find out what personal data that you store. You must
provide a way for users to correct errors in their personal data.

Location
You must not store data in countries where weaker data protection laws apply
unless there is an explicit agreement that the stronger data protection rules will
be upheld.

Security and Privacy © Ian Sommerville 2018: 47

 Privacy policy

• You should to establish a privacy policy that defines how personal and sensitive
information about users is collected, stored and managed.

• Software products use data in different ways, so your privacy policy has to define
the personal data that you will collect and how you will use that data.

• Product users should be able to review your privacy policy and change their
preferences regarding the information that you store.

• Your privacy policy is a legal document and it should be auditable to check that it is
consistent with the data protection laws in countries where your software is sold.

• Privacy policies should not be expressed to users in a long ‘terms and conditions’
document that, in practice, nobody reads.

• The GDPR now require software companies to include a summary of their privacy
policy, written in plain language rather than legal jargon, on their website.

Security and Privacy © Ian Sommerville 2018: 48

 Key points 1
• Security is a technical concept that relates to a software system’s ability to protect itself
from malicious attacks that may threaten its availability, the integrity of the system and/or
its data, and the theft of confidential information.

• Common types of attack on software products include injection attacks, cross-site scripting
attacks, session hijacking attacks, denial of service attacks and brute force attacks.

• Authentication may be based on something a user knows, something a user has, or some
physical attribute of the user.

• Federated authentication involves devolving responsibility for authentication to a third-

party such as Facebook or Google, or to a business’s authentication service.

• Authorization involves controlling access to system resources based on the user’s

authenticated identity. Access control lists are the most commonly-used mechanism to
implement authorization.

• Symmetric encryption involves encrypting and decrypting information with the same secret
key. Asymmetric encryption uses a key pair – a private key and a public key. Information
encrypted using the public key can only be decrypted using the private key.

Security and Privacy © Ian Sommerville 2018: 49

 Key points 2

• A major issue in symmetric encryption is key exchange. The TLS protocol, which is
used to secure web traffic, gets around this problem by using asymmetric encryption
for transferring information used to generate a shared key.

• If your product stores sensitive user data, you should encrypt that data when it is not
in use.

• A key management system (KMS) stores encryption keys. Using a KMS is essential
because a business may have to manage thousands or even millions of keys and may
have to decrypt historic data that was encrypted using an obsolete encryption key.

• Privacy is a social concept that relates to how people feel about the release of their
personal information to others. Different countries and cultures have different ideas on
what information should and should not be private.

• Data protection laws have been made in many countries to protect individual privacy.
They require companies who manage user data to store it securely, to ensure that it is
not used or sold without the permission of users, and to allow users to view and
correct personal data held by the system.

Security and Privacy © Ian Sommerville 2018: 50