Network Security (Course Details) By ASIM SHAHZAD Assistant Professor University Of Engineering And Technology Taxila

 Name:Asim Shahzad  MS Telecom Engineering (I.C.T)  MS Computer Engineering (U.E.T Taxila)  Currently started PhD in area of Solitons propagation in Fiber Optics Communication from U.E.T Taxila   Contact no

Theme of Course  1. Module 1 (Cryptography) Introduction to Security terms and Algorithms Overview of Symmetric and Asymmetric Cryptographic Algorithms  2. Module 2 (Security Architectures and Models) Security in Network Multilayer Security  3. Module 3 (Operations Security) TCSEC (Trusted Computer Security Evaluation Criteria); The Orange Book Vulnerabilities of Networked Applications Worms, viruses, malicious codes arriving from networks, attack on infrastructure  4. Module 4 (Defense Technologies) Protection of information in transit; Application and Transport Layer security Protocols Protection of Networked Applications; Firewalls, and IPS  5. Module 5 (Application and System Development) Kerberos, IPSec, SSL/TLS (Case Studies)  6. Module 6 (Security Management) Security Planning; Physical Security Disaster Recovery Law, Investigation, Ethics; Ethical Hacking

Marks Breakdown  Total Marks150  External marks25  Final 100  Internal Sessional Work 25  Passing Marks75

 Two parts of your course.  How to secure data (data security).  How to secure your networks (network security) we start from data security talk about its various aspects.major concern will be ciphers designing.

Desirable Security Properties  Authenticity  Confidentiality  Integrity  Availability  Accountability and non-repudiation  Freshness  Access control  Privacy of collected information

Cryptology  Some Terminologies  Plain text: The original message  Cipher Text: The coded message  Cipher: algorithm for transforming plaintext to cipher text  Key: info used in cipher; known only to sender/receiver  Encipher (encrypt): converting plaintext to cipher text  Decipher (decrypt): recovering cipher text from plaintext

Contd… Cryptography: study of encryption principles/methods. Cryptanalysis (code breaking): the study of principles/ methods of deciphering cipher text without knowing key. Cryptology: the field of both cryptography and cryptanalysis.

Contd..  Unconditional security No matter how much computer power is available, the cipher cannot be broken since the cipher text provides insufficient information to uniquely determine the corresponding plaintext.  Computational security Given limited computing resources (e.g. time needed for calculations is greater than age of universe), the cipher cannot be broken.

Conventional Encryption Principles  An encryption scheme has five ingredients:  Plaintext  Encryption algorithm  Secret Key  Cipher text  Decryption algorithm  Security depends on the secrecy of the key, not the secrecy of the algorithm

Cryptology Classified along three independent dimensions: 1)Type of encryption operations used for transforming plaintext to cipher text. substitution / transposition / product 2) Number of keys used symmetric - single-key or secret key encryption asymmetric - two-key or public key encryption 3)Way in which plaintext is processed Block stream

Cryptanalysis  Two general approaches to attack an encryption scheme 1) Cryptanalysis. needs encryption algorithm plus some knowledge regarding the plaintext or some sample plain text cipher text pair. 2) Brute-Force attack attacker tries every possible key to decrypt. needs to check so many keys.

Types of Cryptanalysis  Ciphertext only attacker only knows the encryption algorithm & ciphertext  Known plaintext knows the encryption algorithm & ciphertext additionally knows some sample plaintext- ciphertext pairs  Chosen plaintext attacker selects plaintext and obtain ciphertext to attack cipher  Chosen ciphertext select ciphertext and obtain plaintext to attack cipher

Classical Ciphers.Where letters of plaintext are replaced by other letters or by numbers or symbols..Or if plaintext is viewed as a sequence of bits, then substitution involves replacing plaintext bit patterns with cipher text bit patterns.

Caesar Cipher  Earliest known substitution cipher  Devised by Julius Caeser.  First attested use in military affairs.  Replaces each letter by 3rd letter of alphabets  Example:  Plaintext: MEET ME AFTER THE TEA PARTY  Cipher text: PHHW PH DIWHU WKH WHD SDUWB

Contd…  We can generalize Caesar cipher as:  C = E( p) = ( p + k) mod (26)  p = D(C) = (C – k) mod (26)  Where k is the offset e.g., 3 as in our  example  p is the letter to be converted into cipher text  and C is cipher text

 Cryptanalysis of Caeser Cipher  Only have 26 possible ciphers  A maps to A,B,..Z.Could simply try each in turn i.e., using a brute force search  Given cipher text, just try all shifts of letters

CAUTION: QUIZ AHEAD  You are free to leave the class room but if seated, then please be silent  If eyes tried to tilt to fellows paper; either for correction or for soliciting info will cancel you quiz on immediate basis  Exams also checks ability, honesty, zeal and struggle towards problem solving attitude  Initial thesis: “everyone is honest, unless he proves himself otherwise”  Hope that initial conditions (thesis) will remain steady state

 QUIZ NO 01  Find the plain text and Key from the  given cipher text  Cipher Text:  TUSBCMRK MW HMWLSRIWXC

Attacks, Services and Mechanisms  Security Attack: Any action that compromises the security of information.  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 data processing systems and information transfers. A security service makes use of one or more security mechanisms

Security Attacks

CIPHERS  Now we will discuss various ciphers and their working.  Cipher is an algorithm that provides encryption to your data.

Transposition Ciphers  now consider classical transposition or permutation ciphers  these hide the message by rearranging the letter order  without altering the actual letters used  can recognise these since have the same frequency distribution as the original text

Rail Fence cipher  write message letters out diagonally over a number of rows  then read off cipher row by row  eg. write message out as: m e m a t r h t g p r y e t e f e t e o a a t  giving ciphertext MEMATRHTGPRYETEFETEOAAT

Row Transposition Ciphers  a more complex scheme  write letters of message out in rows over a specified number of columns  then reorder the columns according to some key before reading off the rows Key: Plaintext: a t t a c k p o s t p o n e d u n t i l t w o a m x y z Ciphertext: TTNAAPTMTSUOAODWCOIXKNLYPETZ

Product Ciphers  ciphers using substitutions or transpositions are not secure because of language characteristics  hence consider using several ciphers in succession to make harder, but: two substitutions make a more complex substitution two transpositions make more complex transposition but a substitution followed by a transposition makes a new much harder cipher  this is bridge from classical to modern ciphers

Rotor Machines  before modern ciphers, rotor machines were most common product cipher  were widely used in WW2 German Enigma, Allied Hagelin, Japanese Purple  implemented a very complex, varying substitution cipher  used a series of cylinders, each giving one substitution, which rotated and changed after each letter was encrypted  with 3 cylinders have 26 3 =17576 alphabets

Steganography  an alternative to encryption  hides existence of message using only a subset of letters/words in a longer message marked in some way using invisible ink hiding in LSB in graphic image or sound file  has drawbacks high overhead to hide relatively few info bits

Summary  have considered: classical cipher techniques and terminology monoalphabetic substitution ciphers cryptanalysis using letter frequencies Playfair ciphers polyalphabetic ciphers transposition ciphers product ciphers and rotor machines stenography