OSI security architecture

OSI security architecture – Attacks, Services and Mechanisms 

INTRODUCTION
Computer data often travels from one computer to another, leaving the safety of
its protected physical surroundings. Once the data is out of hand, people with bad
intention could modify or forge your data, either for amusement or for their own benefit.
Cryptography can reformat and transform our data, making it safer on its trip
between computers. The technology is based on the essentials of secret codes, augmented
by modern mathematics that protects our data in powerful ways.

 

Computer Security - generic name for the collection of tools designed to protect
data and to thwart hackers
Network Security - measures to protect data during their transmission
Internet Security - measures to protect data during their transmission over a
collection of interconnected networks

 

THE OSI SECURITY ARCHITECTURE

To assess effectively the security needs of an organization and to evaluate and choose
various security products and policies, the manager responsible for security needs some
systematic way of defining the requirements for security and characterizing the
approaches to satisfying those requirements. The OSI security architecture was developed
in the context of the OSI protocol architecture, which is described in Appendix H.
However, for our purposes in this chapter, an understanding of the OSI protocol
architecture is not required.

 

For our purposes, the OSI security architecture provides a useful, if abstract, overview of
many of the concepts.. The OSI security architecture focuses on security attacks,
mechanisms, and services. These can be defined briefly as follows:
Threat

A potential for violation of security, which exists when there is a circumstance,
capability, action, or event that could breach security and cause harm. That is, a threat is
a possible danger that might exploit a vulnerability.

Attack

An assault on system security that derives from an intelligent threat; that is, an intelligent
act that is a deliberate attempt (especially in the sense of a method or technique) to evade
security services and violate the security policy of a system.

Security Attacks, Services And Mechanisms
To assess the security needs of an organization effectively, the manager
responsible for security needs some systematic way of defining the requirements for
security and characterization of approaches to satisfy those requirements. One approach
is to consider three aspects of information security:
Security attack – Any action that compromises the security of information
owned by an organization.
Security mechanism – A mechanism that is designed to detect, prevent or
recover from a security attack.
Security service – A service that enhances the security of the data processing
systems and the information transfers of an organization. The services are
intended to counter security attacks and they make use of one or more security
mechanisms to provide the service.

  
SECURITY SERVICES
The classification of security services are as follows:

Confidentiality: Ensures that the information in a computer system and
transmitted information are accessible only for reading by authorized parties.
Eg., printing, displaying and other forms of disclosure.

Authentication: Ensures that the origin of a message or electronic document is
correctly identified, with an assurance that the identity is not false.

 

Integrity: Ensures that only authorized parties are able to modify computer
system assets and transmitted information. Modification includes writing,
changing status, deleting, creating and delaying or replaying of transmitted
messages.

Non repudiation: Requires that neither the sender nor the receiver of a message
be able to deny the transmission.

Access control: Requires that access to information resources may be controlled
by or the target system.

Availability: Requires that computer system assets be available to authorized
parties when needed.

 

AUTHENTICATION

The assurance that the communicating entity is the one that it claims to be.

Peer Entity Authentication

Used in association with a logical connection to provide confidence in the identity of the
entities connected.

Data Origin Authentication

In a connectionless transfer, provides assurance that the source of received data is as
claimed.

ACCESS CONTROL

The prevention of unauthorized use of a resource (i.e., this service controls who can have
access to a resource, under what conditions access can occur, and what those accessing
the resource are allowed to do).

DATA CONFIDENTIALITY

The protection of data from unauthorized disclosure.

Connection Confidentiality

The protection of all user data on a connection.

Connectionless Confidentiality

The protection of all user data in a single data block

Selective-Field Confidentiality

AUTHENTICATION

The confidentiality of selected fields within the user data on a connection or in a single
data block.

Traffic Flow Confidentiality

The protection of the information that might be derived from observation of traffic flows.

 

Connection Integrity with Recovery

Provides for the integrity of all user data on a connection and detects any modification,
insertion, deletion, or replay of any data within an entire data sequence, with recovery
attempted.

Connection Integrity without Recovery

As above, but provides only detection without recovery.

Selective-Field Connection Integrity

Provides for the integrity of selected fields within the user data of a data block
transferred over a connection and takes the form of determination of whether the selected
fields have been modified, inserted, deleted, or replayed.

Connectionless Integrity

Provides for the integrity of a single connectionless data block and may take the form of
detection of data modification. Additionally, a limited form of replay detection may be
provided.

Selective-Field Connectionless Integrity

Provides for the integrity of selected fields within a single connectionless data block;
takes the form of determination of whether the selected fields have been modified.

NONREPUDIATION

Provides protection against denial by one of the entities involved in a communication of
having participated in all or part of the communication.

Nonrepudiation, Origin

Proof that the message was sent by the specified party.

Nonrepudiation, Destination

Proof that the message was received by the specified party.

 

 SECURITY MECHANISMS
One of the most specific security mechanisms in use is cryptographic techniques.
Encryption or encryption-like transformations of information are the most common
means of providing security. Some of the mechanisms are

 Encipherment

Digital Signature

Access Control

SECURITY ATTACKS
There are four general categories of attack which are listed below.

Interruption
An asset of the system is destroyed or becomes unavailable or unusable. This is
an attack on availability.
e.g., destruction of piece of hardware, cutting of a communication line or
disabling of file management system.

 

Interception

An unauthorized party gains access to an asset. This is an attack on
confidentiality. Unauthorized party could be a person, a program or a
computer.e.g., wire tapping to capture data in the network, illicit copying of files

 

Modification
An unauthorized party not only gains access to but tampers with an asset. This is
an attack on integrity.
e.g., changing values in data file, altering a program, modifying the contents of
messages being transmitted in a network.

Fabrication
An unauthorized party inserts counterfeit objects into the system. This is an attack
on authenticity.
e.g., insertion of spurious message in a network or addition of records to a file.

  
Passive attack
Passive attacks are in the nature of eavesdropping on, or monitoring of, transmissions.
The goal of the opponent is to obtain information that is being transmitted. Passive
attacks are of two types:

 

Release of message contents: A telephone conversation, an e-mail message and a
transferred file may contain sensitive or confidential information. We would like
to prevent the opponent from learning the contents of these transmissions.

Traffic analysis: If we had encryption protection in place, an opponent might still
be able to observe the pattern of the message. The opponent could determine the
location and identity of communication hosts and could observe the frequency
and length of messages being exchanged. This information might be useful in
guessing the nature of communication that was taking place.
Passive attacks are very difficult to detect because they do not involve any alteration
of data. However, it is feasible to prevent the success of these attacks.

Active attacks

These attacks involve some modification of the data stream or the creation of a false
stream. These attacks can be classified in to four categories:

Masquerade – One entity pretends to be a different entity.
Replay – involves passive capture of a data unit and its subsequent transmission
to produce an unauthorized effect.
Modification of messages – Some portion of message is altered or the messages
are delayed or recorded, to produce an unauthorized effect.
Denial of service – Prevents or inhibits the normal use or management of
communication facilities. Another form of service denial is the disruption of an
entire network, either by disabling the network or overloading it with messages so
as to degrade performance.
It is quite difficult to prevent active attacks absolutely, because to do so would require
physical protection of all communication facilities and paths at all times. Instead, the goal
is to detect them and to recover from any disruption or delays caused by them.

 

MCQ

1.We use Cryptography term to transforming messages to make them secure and immune to
a. Change        b. Idle            c. Attacks        d. Defend
Ans: C

2.Cryptography, a word with Greek origins, means
a. Corrupting Data    b. Secret Writing    c. Open Writing    d. Closed Writing
Ans: B

 3.Cryptography can provide
a. entity authentication         b. nonrepudiation of messages
c. confidentiality         d. All of them
Ans: D

4. In computer security, ……………………. means that computer system assets can be
modified only by authorized parities.
a. Confidentiality         b.Integrity         c.Availability         d.Authenticity
Ans: A

5.The type of threats on the security of a computer system or network are ……………………..
i) Interruption ii) Interception  iii) Modification v) Creation v) Fabrication
a. i, ii, iii & iv only     b.ii, iii, iv & v only     c.i, ii, iii & v only     d.All i, ii, iii, iv & v
Ans: C

 2 Marks

• Specify the four categories of security threats?

 

• Interruption
• Interception
• Modification
• Fabrication

• Explain active and passive attack with example?

Passive attack:
Monitoring the message during transmission. Eg: Interception
Active attack:
It involves the modification of data stream or creation of false data stream.
E.g.: Fabrication, Modification, and Interruption

• Define integrity and no repudiation?
• Integrity:

Service that ensures that only authorized person able to modify the message.

• Non repudiation:

This service helps to prove that the person who denies the transaction is true or false.

• Define security mechanism

It is process that is designed to detect prevent, recover from a security attack.
Example: Encryption algorithm, Digital signature, Authentication protocols.

• State why network need security.

When systems are connected through the network, attacks are possible during ransmission time.

• Define confidentiality and authentication.

Confidentiality:
It means how to maintain the secrecy of message. It ensures that the information in a computer system and transmitted information are accessible only for reading by autherised person.
Authentication:
It helps to prove that the source entity only has involved the transaction.

• Specify the basic task for security service

A service that enhances the security of the data processing systems and the
information transfer of an organization. The services are intended to counter
security attack, and they make use of one or more security mechanism to provide
the service.

• Define threat and attack.

Threat:
A potential for violation of security, which exists when there is a circumstance, capability, action or event that could breach security and cause harm. That is, a threat is a possible danger that might exploit a vulnerability
Attack:
an assault on system security that derives from an intelligent threat, that is, an intelligent act that is a deliberate attempt to evade security services and violate the security policy of a system.
 
16Marks

• Write short notes on  Security attacks .
• Explain in detail Security services.
• Explain OSI security architecture.

 

Network Security Model
Saturday, July 02, 2016
3:51 PM

 

 

Symmetric and public key algorithms
Encryption/Decryption methods fall into two categories.

 

Symmetric key

Public key
In symmetric key algorithms, the encryption and decryption keys are known both to
sender and receiver. The encryption key is shared and the decryption key is easily
calculated from it. In many cases, the encryption and decryption keys are the same.
In public key cryptography, encryption key is made public, but it is
computationally infeasible to find the decryption key without the information known to
the receiver.
A MODEL FOR NETWORK SECURITY

 

A message is to be transferred from one party to another across some sort of internet. The
two parties, who are the principals in this transaction, must cooperate for the exchange to
take place. A logical information channel is established by defining a route through the
internet from source to destination and by the cooperative use of communication
protocols (e.g., TCP/IP) by the two principals.

using this model requires us to:

design a suitable algorithm for the security transformation
generate the secret information (keys) used by the algorithm
develop methods to distribute and share the secret information
specify a protocol enabling the principals to use the transformation and
secret information for a security service
  referred conventional / private-key / single-key
sender and recipient share a common key
all classical encryption algorithms are private-key
was only type prior to invention of public-key in 1970‟plaintext - the original
message
Some basic terminologies used :
ciphertext - the coded message
cipher - algorithm for transforming plaintext to ciphertext
key - info used in cipher known only to sender/receiver
encipher (encrypt) - converting plaintext to ciphertext
decipher (decrypt) - recovering ciphertext from plaintext
cryptography - study of encryption principles/methods

cryptanalysis (codebreaking) - the study of principles/ methods of deciphering
ciphertext without knowing key
cryptology - the field of both cryptography and cryptanalysis

 

random nonsense, referred to as cipher text. The encryption process consists of an
algorithm and a key. The key is a value independent of the plaintext. Changing the key
changes the output of the algorithm. Once the cipher text is produced, it may be
transmitted. Upon reception, the cipher text can be transformed back to the original
plaintext by using a decryption algorithm and the same key that was used for encryption.
The security depends on several factors. First, the encryption algorithm must be powerful
enough that it is impractical to decrypt a message on the basis of cipher text alone.
Beyond that, the security depends on the secrecy of the key, not the secrecy of the
algorithm.
·
Two requirements for secure use of symmetric encryption:
–
–
a strong encryption algorithm
a secret key known only to sender / receiver
Y = EK(X)
X = DK(Y)

assume encryption algorithm is known
implies a secure channel to distribute key

 

MCQ

• An asymmetric-key (or public-key) cipher uses

a. 1 Key        b. 2 Key        c. 3 Key        d. 4 Key
Ans: B

• In Asymmetric-Key Cryptography, two keys, e and d, have a special relationship to

a. Others        b. Data            c. Keys         d. Each other
Ans: D

• In Cryptography, original message, before being transformed, is called

a. Simple Text         b. Plain Text         c. Empty Text        d. Filled Text
Ans: B

• An encryption algorithm transforms plaintext into

a. Cipher text         b. Simple Text         c. Plain Text        d. Empty Text
Ans: A

• Original message, before being transformed, is

a. Cipher text         b. plaintext        c. decryption        d. None
Ans: B

• In symmetric key cryptography, key used by sender and receiver is

a. Shared             b. different        c. two keys are used        d. None
Ans: A

• In symmetric-key cryptography, same key is used by

a. One Party         b. Multi Party         c. Third Party         d. Both Party
Ans: D

• In symmetric-key cryptography, key locks and unlocks box is

a. Same             b. shared        c. private        d. public
Ans: A

• Keys used in cryptography are

a. secret key        b. private key        c. public key         d. All of them
Ans: D

2 Marks

• Differentiate symmetric and asymmetric encryption

 

SYMMETRIC	ASYMMETRIC
It is a form of cryptosystem in which encryption and decryption performed using the same key. Eg: DES, AES	It is a form of cryptosystem in which encryption and decryption Performed using two keys. Eg: RSA, ECC

• Compare stream cipher with block cipher with example.

Stream cipher:
Processes the input stream continuously and producing one element at a time.
Example: caeser cipher.
Block cipher:
Processes the input one block of elements at a time producing an output block for each input block. Example: DES.

• Specify the components of encryption algorithm.
•  Plaintext
•  Encryption algorithm
•  Secret key
•  Cipher text
•  Decryption algorithm