Dr Alejandra Flores-Mosri Security Internet Management & Security 06 Learning outcomes At the end of this session, you should be able to: –Describe the

Internet Management & Security 06Dr Alejandra Flores-Mosri

Security Learning outcomes

At the end of this session, you should be able to:

– Describe the reasons for having system and network security

– Relate security services to security attacks– Describe the basic operation of encryption

trhough Feistel cypher structure– Compare different symmetric encryption

algorithms: DES and AES– Design a simple encryption algorithm


Security Introduction

With the high availability of resources on the Internet, security has become a very relevant issue.

The main aim is to protect the resources on the Internet so that they cannot:

– Be accessed

– Be changed

– Be deleted

by non-authorised or malicious users


Security Vulnerability of systems and networks

A

B

C

D

Malicioususer

Malicioususer

Malicioususer

Malicioususer


Security Passive security attacks

Passive attacks– Obtain information being transmitted or stored in

a system– Do not alter the contents of messages or files– Difficult to detect

Solution:– Prevent the attack: data confidentiality– Encrypt information, strongly authenticate

access


Security Active security attacks

Active attacks

– Modify or delete data stored or being transmitted• Masquerade• Replay• Modification• Denial of service

– Easier to detect– Harder to prevent


Security Active security attacks

Solution:

– Authentication– Access control– Data confidentiality– Data integrity– Non-repudiation– Availability


Security Conclusions

Security strategies are important because they:– help maintain good performance of resources on

a network

– guarantee users that their information is safe and private

– deter potential attacks on resources


Security Resources

• Stallings W., Network Security Essentials, 2nd Edition, Prentice Hall, 2002

(Chapter 1)

• RFC 2828 Internet Security Glossary


Security Cryptography

Cryptography modifies the content of a message according to a predetermined pattern only known by sender and receiver with the aim to prevent other parties from reading the content

An encrypted message is:1 Transformed2 Transmitted3 Unchanged

The predetermined pattern or key needs to be transmitted separately


Security Symmetric cryptography

• Message

• Encryption algorithm

• Secret key

• Ciphertext

• Decryption algorithm

(the success of the process relies on the secrecy of the key, but it must be known by the sender and the receiver)


Security Feistel Cipher Structure


Security Data Encryption Standard (DES)

It is a symmetric block cipher algorithm:• 64 bit code• 56 bit key• Sixteen rounds (iterations), hence 16 subkeys

need to be generated

Advantages:No one has found a fatal weakness of the algorithm

Disadvantages:It has been broken by “brute-force” (256 possible keys) in

1998 by the Electronic Frontier Foundation with their DES-cracker


Security Triple DES

• The same as DES but it uses three executions of the full DES algorithm with three different keys

• Used in financial applications

C=EK3[DK2

[EK1[P]]]

C – ciphertextP – plaintext

EK [X] – encryption of X using key K

DK [X] – decryption of X using key K

• Advantage – effective key of 128 bits• Disadvantage – more processing power needed


Security Advanced Encryption Standard (AES)

AES – first thought of to replace 3DES with a lighter algorithm that provides the same security as 3DES

• Block length – 128 bits

• Supports keys of – 128, 192 and 256 bits (most common key is 128)

• NOT a Feistel structure


Security AES


Security AES


Security AES


Security AES


Security Other symmetric algorithms

• IDEA

• Blowfish

• RC5


Security Conclusions

• Encrypted information has more probabilities of remaining private

• Most common symmetrical encryption algorithms use Feistel’s cipher

• The length of the block and the key determine the efficiency of the cipher based algorithms

• AES solves the problem of processing power and key sizes

• The transmission of the key remains a problem


Security Resources

Stallings W., Network Security Essentials, 2nd Edition, Prentice Hall, 2002(Chapter 2)

FIPS Advanced Encryption Standard, http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf

FIPS DES Data Encryption Standard, http://www.itl.nist.gov/fipspubs/fip46-2.htm

Documents

Dr Alejandra Flores-Mosri Security Internet Management & Security 06 Learning outcomes At the end of this session, you should be able to: –Describe the