Information Security Rabie A. Ramadan GUC, Cairo Room C Lecture 3

What do we need to avoid threats, vulnerability, risks and attacks ? Access Control Access Control Cryptography Cryptography Other Methods ….. Other Methods ….. 2

Access Control Topics Access control categories Access control techniques Access control administration Access control models Authentication methods Data ownership Vulnerabilities 3

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 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. 10

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 1What you knowPassword, PIN, Challenge question Type 2What you haveSmart Card Type 3What you areBiometrics

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 18

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 19

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 ….. 23

Cryptography 24

Security Services and Mechanisms 25 International Telecommunication Union Telecommunication Standardization (ITU-T) Provides: Services Mechanisms

Security Services 26 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 27 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 28

Model for Network Security 29 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.

30 Symmetric Cipher Model

31 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.) 32 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 33 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.) 34

Symmetric Cipher Model 35 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 = E K (X) X =D(K,Y) ~ X = D K (Y)

Brute Force Search 36 Always possible to simply try every key Most basic attack, proportional to key size

37 Substitution Ciphers

Lets have Fun 38 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 39 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 40 Earliest known substitution cipher by Julius Caesar first attested use in military affairs replaces each letter by 3 rd one after it E.g. meet me after the toga party PHHW PH DIWHU WKH WRJD SDUWB

Caesar Cipher (Cont.) 41 Transformation : Mathematically give each letter a number a b c d e f g h i j k l m n o p q r s t u v w x y Z Then have Caesar cipher as: C = E(p) = (p + k) mod (26) p = D(C) = (C – k) mod (26)

Caesar Cipher (Cont.) 42 Cryptanalysis Only have 26 possible ciphers A maps to A,B,..Z Could simply try each in turn

Monoalphabetic Cipher 43 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: DKVQFIBJWPESCXHTMYAUOLRGZN Plaintext: ifwewishtoreplaceletters Ciphertext: WIRFRWAJUHYFTSDVFSFUUFYA

Monoalphabetic Cipher Security 44 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 45

Playfair Cipher 46 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 47 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 MONAR CHYBD EFGI/JK LPQST UVWXZ

Playfair Rules 48 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 49 Based on Playfair encryption, encrypt the word “Hello” Key : Note: The key is an arrangement of all of the alphabetic letters LGDBA QMHEC URNI/JF XVSOK ZYWTP

Answer 50 Step 1: Group the letters He ll o 1 st 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 lo  BX -- 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 51 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 52 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 53 Simplest polyalphabetic substitution cipher effectively multiple caesar ciphers key is multiple letters long K = k1 k2... kd i th letter specifies i th 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 55 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 56 have multiple ciphertext letters for each plaintext letter Letter frequencies are obscured But not totally lost

Autokey Cipher 57 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 58 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

59 Transposition/Permutation Ciphers

Transposition (Cont.) 60  The letters of the message are rearranged  Columnar transposition  The number of columns is required  Example: THIS IS A MESSAGE TO SHOW HOW A COLMUNAR TRANSPOSITION WORKS

Transposition (Cont.) 61 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 62 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 63  Stream  converts one symbol of plaintext into a symbol of ciphertext  Block  encrypts a group of plaintext symbols as one block.