Information Security

Rabie A. Ramadan

GUC, Cairo

Rabie.ramadan@guc.edu.eg

Room C7 -310

Lecture 3

What do we need to avoid threats , vulnerability, risks and attacks ?

Access Control Access Control

Cryptography Cryptography

Other Methods …..Other Methods …..

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Access Control Topics

Access control categories Access control techniques Access control administration Access control models Authentication methods Data ownership Vulnerabilities

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Access Control Definition of access control:

• It is a collection of methods and components that supports

• confidentiality

• integrity Goal: allow only authorized subjects to access permitted

objects• Subject

• The entity that requests access to a resource

• Object

• The resource a subject attempts to access

Access Control

Least privilege philosophy

• A subject is granted permissions needed to accomplish required tasks and nothing more

Information leak

• Lack of controls lets people without need to access data

• E.g., physician needs data about the patient’s health and not about the insurance

Controls Controls

• Mechanisms put into place to allow or disallow object access Controls organized into different categories

• Administrative

• enforce security rules through policies

• E.g. security awareness training

• Logical / technical controls

• implement object access restrictions

• E.g. password , encryption

• Physical

• limit physical access to hardware

• E.g. Fences , Walls , locked doors

Access Control Techniques

Techniques are based on the organization’s needs and their impact to the users

Considerations include

• Level of security required

• User and environmental impact of security measures

Techniques differ in

• The way objects and subjects are identified

• How decisions are made to approve or deny access

• Policies governing access

Access Control Designs

Access control designs define rules for users accessing files or devices

Three common access control designs• Mandatory access control

• Discretionary access control

• Task-based access control

Mandatory Access Control Assigns a security label to each subject and object Matches label of subject to label of object to determine when access

should be granted E.g Military Information classification Top Secret (TS)

• The highest level of classification of information on a national level. Such material would cause "exceptionally grave damage" to national security if publicly available.

Secret

• Such material would cause "serious damage" to national security if publicly available.

Mandatory Access Control Confidential

• Such material would cause "damage“ to national security if publicly available.

Restricted

• Such material would cause "undesirable effects" if publicly available. Some countries do not have such a classification.

Unclassified

• Technically not a classification level, but is used for government documents that do not have a classification listed above. Such documents can sometimes be viewed by those without security clearance.

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Discretionary Access Control

Uses identity of subject to decide when to grant an access request

All access to an object is defined by the object owner Most common design in commercial operating systems

• Generally less secure than mandatory control

• Generally easier to implement and more flexible Includes

• Identity-based access control

• Access control lists (ACLs)

Task-based Access Control or Nondiscretionary Access Control

Uses a subject’s role or task to grant or deny object access• Task objects or requirements will be granted to the user

Task-based access list may contain just one member, if necessary

Lattice-based control is a variation of non-discretionary control

• Relationship between subject and object has a set of access boundaries that define rules and conditions for access

Access Control Administration Once the access control technique is chosen , we need to

decide on the way these techniques can be administrated

• Implemented as centralized, decentralized, or hybrid

Centralized access control administration

• All requests go through a central authority

• Administration is relatively simple

• Single point of failure, sometimes performance bottlenecks

Access Control Administration

Decentralized access control administration• Object access is controlled locally rather than centrally

• Put the control administrator closer to the object in question

• More difficult administration• Objects may need to be secured at multiple locations

• More stable• Not a single point of failure

• Usually implemented using security domains

Accountability

System auditing used by administrators to monitor

• Who is using the system

• What users are doing

Logs can trace events back to originating users

Process of auditing can have a negative effect on system performance

• Must limit data collected in logs

• Clipping levels set thresholds for when to start collecting data

Authentication Methods

Two-factor authentication uses two phases

• Identification

• Authentication

Security practices often require input from multiple categories of authentication techniques

Most complex authentication mechanism is biometrics (detection and classification of a subject’s physical attributes)

Authentication Methods

Type 1 What you know Password, PIN,

Challenge question

Type 2 What you have Smart Card

Type 3 What you are Biometrics

Authentication Methods

Type 1 -- What you know:

• Password , PIN, and Challenge question Password must be difficult to guess and easy to remember

• At least 6 characters

• Contains at least one number or any punctuation character

• Do not use dictionary words

• Do not use common personal data

• Never write down your password

Type 2 -- What you have:

• More complex than Type 1 but it is more secure since it uses special devices to read your cards for example

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Authentication Methods

Type 3---What you are

• Fingerprint, Hand geometry , Voice print, Retina/iris scan, or signature

• Very complex system due to the imperfection of the nature of biometrics analysis

• False Rejection rate (FRR) : the of filature of detection the right subject

• False Acceptance Rate (FAR) : the rate of acceptance of invalid subjects

• Crossover Error Rate (CER) : balance between FRR and FAR

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Data Ownership Different layers of responsibility for ensuring security of

organization’s information

Data owner• Bears ultimate responsibility, sets classification levels

Data custodian• Enforces security policies, often a member of IT

department Data user

• Accesses data on a day-to-day basis• responsible for following the organization’s security

policies

Vulnerabilities

Brute force attack

• Try all possible combinations of characters to satisfy Type 1 authentication (password guessing)

Dictionary attack

• Subset of brute force

• Instead of all possible combinations, uses a list of common passwords

Spoofing attack

• Create fake login program, prompt for User ID, password

• Return login failure message, store captured information

Policies for Vulnerability Handling

Log all data – login, transaction Analyze data in real time Set security alerts based on data analysis Develop scenarios for system shut off Disseminate policies related to vulnerability

handling

What do we need to avoid threats , vulnerability, risks and attacks ?

Access Control Access Control

Cryptography Cryptography

Other Methods …..Other Methods …..

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Cryptography

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Security Services and Mechanisms

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International Telecommunication Union Telecommunication Standardization (ITU-T) Provides:

• Services

• Mechanisms

Security Services

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Authentication - assurance that the communicating entity is the one claimed

Access Control - prevention of the unauthorized use of a resource

Data Confidentiality –protection of data from unauthorized disclosure

Data Integrity - assurance that data received is as sent by an authorized entity

Non-Repudiation - protection against denial by one of the parties in a communication

Security Mechanisms

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Specific security mechanisms:• Implemented on specific layer (OSI model)

• Encipherment, digital signatures, access controls, data integrity, authentication exchange, routing control, notarization

Pervasive security mechanisms:• Not related to a specific layer

• Trusted functionality, security labels, event detection

Model for Network Security

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Model for Network Security

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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.

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Symmetric Cipher Model

Symmetric Cipher Model

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Known as:• Conventional Encryption

• Single-Key Encryption

Plaintext• Original text/msg

Ciphertext• Coded msg

Enciphering/Encryption• The process of converting the plaintext to ciphertext

Deciphering/Decryption • The process of converting the ciphertext to plaintext

Symmetric Cipher Model (Cont.)

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Cryptography • The developed encryption schemes

Cryptanalysis • Techniques used to get the plaintext out of the ciphertext without

prior knowledge to the encryption scheme (breaking the code)

Cryptology • Both the cryptography and cryptanalysis

More Definitions

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Unconditional Security • The ciphertext provides insufficient information to

uniquely determine the corresponding plaintext.

Computational Security • The time needed for calculations is greater than

age of universe

Symmetric Cipher Model (Cont.)

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Symmetric Cipher Model

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Requirements • Strong Key the opponent can not figure it out even if he/she has

a number of ciphertexts

• The key must be exchanged through a secure channel

• Y = E(K,X) ~ Y = EK(X)

• X =D(K,Y) ~ X = DK(Y)

Brute Force Search

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Always possible to simply try every key Most basic attack, proportional to key size

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Substitution Ciphers

Lets have Fun

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You are spying on your friend Ahmed while he is chatting with John, you received the following message:

“Ygjcxgvqmnnvjgrgumfgpv”

Can you decrypt this message?

Answer

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Ahmed is telling John:

“Ygjcxgvqmnnvjgrgumfgpv”

“We have to kill the president” Encryption Key:

• Replacement Table Plaintext ABCDEFGHIJKLMNOPQRSTUVWXYZ Ciphertext CDEFGHIJKLMNOPQRSTUVWXYZAB

Encryption Technique • Each letter is replaced by the second one after it

• Remove blanks

Caesar Cipher

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Earliest known substitution cipher by Julius Caesar first attested use in military affairs replaces each letter by 3rd one after it

E.g.meet me after the toga party

PHHW PH DIWHU WKH WRJD SDUWB

Caesar Cipher (Cont.)

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Transformation :

Mathematically give each letter a numbera b c d e f g h i j k l m0 1 2 3 4 5 6 7 8 9 10 11 12n o p q r s t u v w x y Z13 14 15 16 17 18 19 20 21 22 23 24 25

Then have Caesar cipher as:C = E(p) = (p + k) mod (26)p = D(C) = (C – k) mod (26)

Caesar Cipher (Cont.)

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Cryptanalysis

• Only have 26 possible ciphers

•A maps to A,B,..Z

• Could simply try each in turn

Monoalphabetic Cipher

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Rather than just shifting the alphabet Could shuffle (jumble) the letters arbitrarily Each plaintext letter maps to a different random

ciphertext letter The key is 26 letters long

Plain: abcdefghijklmnopqrstuvwxyz Cipher: DKVQFIBJWPESCXHTMYAUOLRGZNPlaintext: ifwewishtoreplacelettersCiphertext: WIRFRWAJUHYFTSDVFSFUUFYA

Monoalphabetic Cipher Security

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now have a total of 26! = 4 x 1026 keys with so many keys, might think is secure but would be !!!WRONG!!!

Language Characteristics Problem

• Using the occurrence frequency of each letter , we can deduce the letters in the ciphertext

English Letter Frequencies

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Playfair Cipher

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Invented by Charles Wheatstone in 1854, but named after his friend Baron Playfair.

Encrypts multiple letters

Uses Playfair Matrix

Uses some of the rules to interpret the matrix

Playfair Key Matrix

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A 5X5 matrix of letters based on a keyword Fill in letters of keyword (Avoid repetition) Fill rest of matrix with other letters E.g. using the keyword MONARCHY

M O N A R

C H Y B D

E F G I/J K

L P Q S T

U V W X Z

Playfair Rules

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Plaintext encrypted two letters at a time: • if a pair is a repeated letter, insert a filler like 'X',

• eg. "balloon" encrypts as "ba lx lo on"

• If both letters fall in the same row, replace each with letter to right (wrapping back to start from end), • eg. “ar" encrypts as "RM"

• If both letters fall in the same column, replace each with the letter below it (again wrapping to top from bottom), • eg. “mu" encrypts to "CM"

• Otherwise each letter is replaced by the one in its row in the column of the other letter of the pair,• eg. “hs" encrypts to "BP", and “ea" to "IM" or "JM" (as desired)

Group Activity

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Based on Playfair encryption, encrypt the word

“Hello”

Key :

Note: The key is an arrangement of all of the alphabetic letters

L G D B A

Q M H E C

U R N I/J F

X V S O K

Z Y W T P

Answer

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Step 1: Group the letters

• He ll o

• 1st rule repeated letters ll

• He lx lo Step 2: find the corresponding text in the key

• He EC - rule 2 H and e on the same row (replace each with letter to right) EC

• Lx QZ -- rule 3 L and x at the same column (replace each with the letter below it) QZ

• loBX -- rule 4 l and o at different rows and columns (replaced by the one in its row in the column of the other letter of the pair)

E (Hello) “ECQZBX”

Security of the Playfair Cipher

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Security much improved over monoalphabetic

Since have 26 x 26 = 676 diagrams

Was widely used for many years (eg. US & British military in WW1)

It can be broken, given a few hundred letters since still has much of plaintext structure

Polyalphabetic Ciphers

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Another approach to improving security is to use multiple cipher alphabets

Makes cryptanalysis harder with more alphabets to guess and flatter frequency distribution

Use a key to select which alphabet is used for each letter of the message

Use each alphabet in turn Repeat from start after end of key is reached

Vigenère Cipher

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Simplest polyalphabetic substitution cipher effectively multiple caesar ciphers key is multiple letters long K = k1 k2 ... kd ith letter specifies ith alphabet to use use each alphabet in turn repeat from start after d letters in message decryption simply works in reverse

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Example

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eg using repeated keyword deceptive

key: deceptivedeceptivedeceptive

plaintext: wearediscoveredsaveyourself

ciphertext:ZICVTWQNGRZGVTWAVZHCQYGLMGJ

From the previous table lookup the key letter then the

plain text letter.

The cipher letter is the intersection letter

Security of Vigenère Ciphers

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have multiple ciphertext letters for each plaintext letter

Letter frequencies are obscured

But not totally lost

Autokey Cipher

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Ideally want a key as long as the message Vigenère proposed the autokey cipher The keyword is prefixed to message as key Still have frequency characteristics to attack

Eg. given key deceptive

key: deceptivewearediscoveredsav

plaintext: wearediscoveredsaveyourself

ciphertext: ZICVTWQNGKZEIIGASXSTSLVVWLA

One-Time Pad

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Select a random key that is equal to the message length.

Use a table structure such as Vigenère table

Problems: • Generating long random keys

• Bandwidth problem sending the key as long as the Msg

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Transposition/Permutation Ciphers

Transposition (Cont.)

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The letters of the message are rearranged

Columnar transpositionThe number of columns is required

Example:

THIS IS A MESSAGE TO SHOW HOW A COLMUNAR TRANSPOSITION WORKS

Transposition (Cont.)

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T H I S I S A M E S S A G E T O S H O W H O W A C O L M U N A R T R A N S P O S I T I O N W O R K S

tssoh oaniw haaso lrsto imghw utpir seeoa mrook istwc nasna

Group Activity

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Given the following message

“ This is the second lecture”

Divide the message onto a block of 5 letters block Transpose the message Use Autokey cipher to encrypt the result

• Key : “ NetworkSecurity”

Stream Vs. Block Ciphers

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Stream converts one symbol of plaintext into a symbol of ciphertext

Block encrypts a group of plaintext symbols as one block.