This document discusses classical encryption techniques including monoalphabetic substitution ciphers like the Caesar cipher and cryptanalysis using letter frequencies. It also covers the Playfair cipher, polyalphabetic ciphers like the Vigenère cipher, transposition ciphers, product ciphers combining multiple techniques, and steganography for hiding messages. Rotor machines like the Enigma machine are presented as early examples of complex ciphers before the development of modern cryptography.
https://mloey.github.io/courses/security2017.html
https://www.youtube.com/watch?v=td_8AM80DUA&list=PLKYmvyjH53q13_6aS4VwgXU0Nb_4sjwuf&index=2&t=37s
We will discuss the following: Symmetric Encryption, Substitution Techniques, Caesar Cipher, Monoalphabetic Cipher, Playfair Cipher, Hill Cipher
The Roman number system was very cumbersome because there was no concept ... Historical pen and paper ciphers used in the past are sometimes known as ...
In today's high technology environment, organizations are becoming more and more dependent on their information systems. The public is increasingly concerned about the proper use of information, particularly personal data. The threats to information systems from criminals and terrorists are increasing. Many organizations will identify information as an area of their operation that needs to be protected as part of their system of internal control.
Computer and Network Security is the collection of technologies, standards, policies and management practices that are used in order to obtain a high level of security.
The aim of this course is to explore security fundamentals related to computer data, information and Network. It details the methods of attacks along with security principles.
The official learning outcome for this course is: Upon successful completion of the course the students:
• Must know the basic concepts related to computer and network security.
• Must know how to apply the techniques related to data and information.
A combination of lectures and practical sessions will be used in this course in order to achieve the aim of the course.
By MSc. Karwan Mustafa Kareem
Symmetric Cipher Model,BruteForce attack, Cryptanalysis,Advantages of Symmetric cryptosystem,Model of conventional Encryption, model of conventional cryptosystem,Cryptography,Ciphertext,Plaintext,Decryption algorithm,Diadvantages of Symmetric Cryptosystem,Types of attacks on encrypted messages,Average time required for exhaustive key search
https://mloey.github.io/courses/security2017.html
https://www.youtube.com/watch?v=td_8AM80DUA&list=PLKYmvyjH53q13_6aS4VwgXU0Nb_4sjwuf&index=2&t=37s
We will discuss the following: Symmetric Encryption, Substitution Techniques, Caesar Cipher, Monoalphabetic Cipher, Playfair Cipher, Hill Cipher
The Roman number system was very cumbersome because there was no concept ... Historical pen and paper ciphers used in the past are sometimes known as ...
In today's high technology environment, organizations are becoming more and more dependent on their information systems. The public is increasingly concerned about the proper use of information, particularly personal data. The threats to information systems from criminals and terrorists are increasing. Many organizations will identify information as an area of their operation that needs to be protected as part of their system of internal control.
Computer and Network Security is the collection of technologies, standards, policies and management practices that are used in order to obtain a high level of security.
The aim of this course is to explore security fundamentals related to computer data, information and Network. It details the methods of attacks along with security principles.
The official learning outcome for this course is: Upon successful completion of the course the students:
• Must know the basic concepts related to computer and network security.
• Must know how to apply the techniques related to data and information.
A combination of lectures and practical sessions will be used in this course in order to achieve the aim of the course.
By MSc. Karwan Mustafa Kareem
Symmetric Cipher Model,BruteForce attack, Cryptanalysis,Advantages of Symmetric cryptosystem,Model of conventional Encryption, model of conventional cryptosystem,Cryptography,Ciphertext,Plaintext,Decryption algorithm,Diadvantages of Symmetric Cryptosystem,Types of attacks on encrypted messages,Average time required for exhaustive key search
Information and network security 12 classical substitution ciphersVaibhav Khanna
There are two basic building blocks of all encryption techniques: substitution and transposition. A substitution technique is one in which the letters of plaintext are replaced by other letters or by numbers or symbols
The Future Agriculture Industry with Artificial
Intelligence (AI) based TechnologyAuthor: Umakant Bhaskar Gohatre
AI (Artificial Intelligence) in agriculture refers to the use of advanced technologies and algorithms to
improve various aspects of farming and crop management. It involves leveraging data, machine
learning, computer vision, and other AI techniques to optimize agricultural processes, increase
productivity, reduce resource waste, and make informed decisions. Here are some key applications of
AI in agriculture
1. Crop Monitoring and Disease Detection:
• AI can analyze data from various sources such as satellite imagery, drones, and IoT
sensors to monitor crop health and detect diseases, pests, or nutrient deficiencies.
• Machine learning algorithms can process large datasets to identify patterns and
indicators of crop stress, enabling early intervention and targeted treatment.
2. Precision Farming:
• AI-based systems can collect and analyze data on soil conditions, weather patterns, and
historical crop performance to optimize planting, irrigation, fertilization, and pesticide
application.
• By integrating data from sensors, drones, and other devices, AI can provide real-time
recommendations for precise and site-specific farming practices, reducing costs and
environmental impact.
3. Autonomous Farming:
• Powered robots and autonomous vehicles can perform tasks such as planting,
harvesting, and weeding with precision and efficiency.
• Computer vision algorithms enable machines to identify and differentiate between crops,
weeds, and other objects in the field, allowing for targeted actions and selective
treatments.
4. Yield Prediction and Forecasting:
• By analysing historical data, weather patterns, and other factors, AI algorithms can
predict crop yields, helping farmers make better decisions regarding planting schedules,
resource allocation, and market planning.
5. Livestock Monitoring
• AI-based systems can monitor the health and behavior of livestock using computer
vision and sensor technologies.
• Facial recognition and behavioral analysis can identify individual animals, detect signs
of distress or illness, and optimize feeding and breeding programs.
6. Supply Chain Optimization:
• AI can optimize the logistics and supply chain management in agriculture, improving
traceability, reducing waste, and enhancing efficiency.
• Predictive analytics can help anticipate market demand, optimize transportation routes,
and streamline inventory management.
7. Decision Support Systems:
• AI can provide farmers with decision support tools, analyzing complex data and
providing actionable insights.
• By considering multiple factors such as weather, market prices, and historical data, AI
systems can recommend optimal planting strategies, input management, and risk
mitigation measures.
The integration of AI in agriculture holds great potential to address the challenges faced by the industry,
CMOS (complementary metal oxide semiconductor) technology continues to be the
dominant technology for fabricating integrated circuits (ICs or chips). This dominance
will likely continue for the next 25 years and perhaps even longer. Why? CMOS
technology is reliable, manufacturable, low power, low cost, and, perhaps most
importantly, scalable. The fact that silicon integrated circuit technology is scalable was
observed and described in 1965 by Intel founder Gordon Moore. His observations are
now referred to as Moore's law and state that the number of devices on a chip will double
every 18 to 24 months. While originally not specific to CMOS, Moore's law has been
fulfilled over the years by scaling down the feature size in CMOS technology. Whereas
the gate lengths of early CMOS transistors were in the micrometer range (long-channel
devices) the feature sizes of current CMOS devices are in the nanometer range
(short-channel devices).
To encompass both the long- and short-channel CMOS technologies in this book,
a two-path approach to custom CMOS integrated circuit design is adopted. Design
techniques are developed for both and then compared. This comparison gives readers
deep insight into the circuit design process. While the square-law equations used to
describe MOSFET operation that students learn in an introductory course in
microelectronics can be used for analog design in a long-channel CMOS process they are
not useful when designing in short-channel, or nanometer, CMOS technology. The
behavior of the devices in a nanometer CMOS process is quite complex. Simple
equations to describe the devices' behavior are not possible. Rather electrical plots are
used to estimate biasing points and operating behavior. It is still useful, however, for the
student to use mathematical rigor when learning circuit analysis and design and, hence,
the reason for the two-path approach. Hand calculations can be performed using a
long-channel CMOS technology with the results then used to describe how to design in a
nano-CMOS process.
Question Bank: Network Management in TelecommunicationModule 1: Introduction of Network Management
1] What problem would you expect the NMS to resolve, and how?
2] What are the Challenges of IT Manager?
3] Explain trouble ticket administration?
4] Draw Network Management Dumb bell architecture.
5] In absence of a sophisticated NMS, explain the methods used for Management in an
organization.
6] List some common network problems.
7] Why NMS is required?
8] Draw the Dumbbell architecture for Network management.
9] What is the goal of Network Management?
Pre 1990: People are not connected
1990: Connecting People to Information1990: Connecting People to Information
2000: Connecting People to People2000: Connecting People to Peopl
LRU Replacement Policy
The Least Recently Used replacement policy chooses to
replace the page which has not been referenced for the longest time.
This policy assumes the recent past will approximate the immediate
future. The operating system keeps track of when each page was
referenced by recording the time of reference or by maintaining a
stack of references
Table of Contents
Copyright
Endorsements
Preface
About the Author
Plitt J: Background
Oiapt« 1. Data Communications and Networl< Management Overview
Section 1.1. Analogy cl Telephone Network Management
Section 1.2. Data (Computer) and Telea>mmunicatlon Network
Section 1.3. Distributed CCmputing Environment
Section 1.4. TCP/IP-Based Networks: Internet and Intranet
Section 1.5. Communication Protocols and Standards
Section 1.6. Networks, Systems, and Services
Section 1.7. case Histories on Network, System, ard Servics Management
Section 1.8. Challenges of IT Managers
Section 1.9. Network Management : Goals, Organization, and Functions
Section 1.10. Network Management Architecture and Organization
Section 1.11. Network Management Perspectives
Section 1.1.2. NMS Platform
Section 1.13. CUrrent Status and Future cl Network Mana{jement
Summary
Exercises
Chapter 2. Review of Information Nelwor1< and Technolog
Euler's method is a numerical method to solve first order first degree differential equation with a given initial value. It is the most basic explicit method for numerical integration of ordinary differential equations and is the simplest Runge–Kutta method.
The Euler method is a first-order method, which means that the local error (error per step) is proportional to the square of the step size, and the global error (error at a given time) is proportional to the step size. The Euler method often serves as the basis to construct more complex methods, e.g., predictor–corrector method
Mini Project fo BE Engineering students Smt. Indira Gandhi College of Engineering,
Navi Mumbai
Department of Electronics and Telecommunication Engineering
Subject In charge: Umakant Bhaskar Gohatre, Assistant Professor
List of Mini Projects:
• Water Level Controller using 8051 Microcontroller: Here we are designing the
circuit which is used to detect and control the water level automatically in overhead
tank using 8051 microcontroller. It is used in industries to control the liquid level
automatically.
• Password Based Door Lock System using 8051 Microcontroller: This system
demonstrates a password based door lock system wherein once the correct code or
password is entered, the door is opened and the concerned person is allowed access to
the secured area. After some time, the door would be closed. Read this post completely
to get more information.
• Car Parking Guard Circuit Using Infrared Sensor: This circuit helps the person in
the driving seat in such a way that it gives an alarm if there is any obstacle or a wall
while parking or while driving in reverse. It is very useful in our real life.
• Battery Charger Circuit Using SCR: Here is the circuit diagram of battery charger
circuit using Silicon Controlled Rectifier. SCR can be used in half wave rectifier, full
wave rectifier, inverter circuits, power control circuits, etc.
• Interfacing GPS with 8051 Microcontroller: In this interfacing of GPS with 8051
circuit, GPS module calculates the position by reading the signals that are transmitted
by satellites.
• Speed Control of DC Motor Using Pulse Width Modulation: This pulse width
modulation technique is the more efficient way to proceed to manage the speed of our
DC motor manually.
• • Metal Detector Circuit: This is a simple metal detector circuit which is very useful
for checking the person in shopping malls, hotels, cinema halls to ensure that person is
not carrying any explosive metals or illegal things like guns, bombs etc.
Mini Project for Engineering Students BE or Btech Engineering students Smt. Indira Gandhi College of Engineering,
Navi Mumbai
Department of Electronics and Telecommunication Engineering
Subject In charge: Umakant Bhaskar Gohatre, Assistant Professor
List of Mini Projects:
• Fire Alarm with Siren Sound: This circuit alerts us when there is a fire accident at home
by ringing a siren sound instead of a buzzer.
• Mosquito Repellent Circuit: Here is the simple electronic mosquito repellent circuit which
can produce ultrasound in the frequency range of 20-38 kHz, which can scare away mosquitoes.
• Electronic Letter Box: This is a simple circuit which helps in finding out any letter dropped
in our box by stopping the LED lights attached in this circuit.
• Dummy Alarm Circuit: The main principle of the circuit is to flash an LED for every 5
seconds. The circuit consists of 7555 timer IC as main component.
• DTMF Based Home Automation System Circuit: This is a simple and very useful circuit
in our real life named DTMF controlled home appliances system. It helps to control the home
appliances using DTMF technology.
• Ding Dong Sound Generator Circuit: This is ding dong sound generator circuit is designed
using 555 timer IC in astable mode. It can be used as doorbell. With some modifications, it can
be used to produce different sounds. Read this post for complete details.
• Digital Voltmeter Circuit using ICL7107: Here we designed a analog to digital converter
working as a digital voltmeter using a low power three and half digit A/D converter ICL7107
having internal 7 segment decoders, display drivers, a reference and a clock.
• Digital Temperature Sensor: The main principle of this circuit is to display the digital
temperature value. These are mainly used in environmental applications.
• Digital Stopwatch Circuit: This is a simple circuit that displays count from 0 to 59,
representing a 60 second time interval. It consists of a 555 timer to produce the clock pulses
and two counter ICs to carry out the counting operation.
• Basic Logic Gates Using NAND Gate: We are all well known that NOT, AND, OR are the
basic logic gates. Here we have shown how to design these basic logic gates using one of the
universal gates – NAND Gate.
Ballistics is the field of mechanics that worries with the starting, flight conduct and effect impacts of shots, particularly gone weapon weapons, for example, slugs, unguided bombs, rockets or something like that; the science or craft of structuring and quickening shots in order to accomplish an ideal execution.
A ballistic body is a free-moving body with energy which can be liable to powers, for example, the powers applied by pressurized gases from a weapon barrel or a pushing spout, typical power by rifling, and gravity and air haul during flight.
A ballistic rocket is a rocket that is guided distinctly during the generally concise beginning period of fueled flight and the direction is in this way represented by the laws of traditional mechanics; rather than (for instance) a voyage rocket which is efficiently guided in controlled flight like a fixed-wing air ship.Projectile launchers
Throwing is the starting of a shot by hand. Albeit some different creatures can toss, people are curiously great hurlers because of their high expertise and great planning abilities, and it is accepted this is a developed attribute. Proof of human tossing goes back 2 million years. The 90 mph tossing velocity found in numerous competitors far surpasses the speed at which chimpanzees can toss things, which is around 20 mph. This capacity mirrors the capacity of the human shoulder muscles and ligaments to store flexibility until it is expected to drive an item.
Sling
Introduction
Cyber Crime
- What Is Cyber Crime?
- Types Of Cyber Crime
Cyber Security
- What Is Cyber Security?
- Top Seven Cyber Safety Actions
- Cyber Safety At Work & Hom
Water scarcity is the lack of fresh water resources to meet the standard water demand. There are two type of water scarcity. One is physical. The other is economic water scarcity.
Event Management System Vb Net Project Report.pdfKamal Acharya
In present era, the scopes of information technology growing with a very fast .We do not see any are untouched from this industry. The scope of information technology has become wider includes: Business and industry. Household Business, Communication, Education, Entertainment, Science, Medicine, Engineering, Distance Learning, Weather Forecasting. Carrier Searching and so on.
My project named “Event Management System” is software that store and maintained all events coordinated in college. It also helpful to print related reports. My project will help to record the events coordinated by faculties with their Name, Event subject, date & details in an efficient & effective ways.
In my system we have to make a system by which a user can record all events coordinated by a particular faculty. In our proposed system some more featured are added which differs it from the existing system such as security.
About
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Technical Specifications
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
Key Features
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface
• Compatible with MAFI CCR system
• Copatiable with IDM8000 CCR
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
Application
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Overview of the fundamental roles in Hydropower generation and the components involved in wider Electrical Engineering.
This paper presents the design and construction of hydroelectric dams from the hydrologist’s survey of the valley before construction, all aspects and involved disciplines, fluid dynamics, structural engineering, generation and mains frequency regulation to the very transmission of power through the network in the United Kingdom.
Author: Robbie Edward Sayers
Collaborators and co editors: Charlie Sims and Connor Healey.
(C) 2024 Robbie E. Sayers
COLLEGE BUS MANAGEMENT SYSTEM PROJECT REPORT.pdfKamal Acharya
The College Bus Management system is completely developed by Visual Basic .NET Version. The application is connect with most secured database language MS SQL Server. The application is develop by using best combination of front-end and back-end languages. The application is totally design like flat user interface. This flat user interface is more attractive user interface in 2017. The application is gives more important to the system functionality. The application is to manage the student’s details, driver’s details, bus details, bus route details, bus fees details and more. The application has only one unit for admin. The admin can manage the entire application. The admin can login into the application by using username and password of the admin. The application is develop for big and small colleges. It is more user friendly for non-computer person. Even they can easily learn how to manage the application within hours. The application is more secure by the admin. The system will give an effective output for the VB.Net and SQL Server given as input to the system. The compiled java program given as input to the system, after scanning the program will generate different reports. The application generates the report for users. The admin can view and download the report of the data. The application deliver the excel format reports. Because, excel formatted reports is very easy to understand the income and expense of the college bus. This application is mainly develop for windows operating system users. In 2017, 73% of people enterprises are using windows operating system. So the application will easily install for all the windows operating system users. The application-developed size is very low. The application consumes very low space in disk. Therefore, the user can allocate very minimum local disk space for this application.
Student information management system project report ii.pdfKamal Acharya
Our project explains about the student management. This project mainly explains the various actions related to student details. This project shows some ease in adding, editing and deleting the student details. It also provides a less time consuming process for viewing, adding, editing and deleting the marks of the students.
Industrial Training at Shahjalal Fertilizer Company Limited (SFCL)MdTanvirMahtab2
This presentation is about the working procedure of Shahjalal Fertilizer Company Limited (SFCL). A Govt. owned Company of Bangladesh Chemical Industries Corporation under Ministry of Industries.
1. CRYPTOGRAPHY AND
NETWORK SECURITY
FOURTH EDITION, BY WILLIAM STALLINGS, LECTURE SLIDES BY LAWRIE BROWN
PRESENTED BY
UMAKANT BHASKAR GOHATRE
ASSISTANT PROFESSOR, SMT. INDIRA GANDHI COLLEGE OF ENGINEERING, NAVI
MUMBAI
2. CLASSICAL ENCRYPTION
TECHNIQUES
Many savages at the present day regard their
names as vital parts of themselves, and therefore
take great pains to conceal their real names, lest
these should give to evil-disposed persons a
handle by which to injure their owners.
—The Golden Bough, Sir James George Frazer
3. SYMMETRIC ENCRYPTION
• or 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’s
• and by far most widely used
4. SOME BASIC TERMINOLOGY
• plaintext - original message
• ciphertext - 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) - study of principles/
methods of deciphering ciphertext without knowing key
• cryptology - field of both cryptography and cryptanalysis
6. REQUIREMENTS
• two requirements for secure use of symmetric
encryption:
• a strong encryption algorithm
• a secret key known only to sender / receiver
• mathematically have:
Y = EK(X)
X = DK(Y)
• assume encryption algorithm is known
• implies a secure channel to distribute key
7. CRYPTOGRAPHY
• characterize cryptographic system by:
• type of encryption operations used
• substitution / transposition / product
• number of keys used
• single-key or private / two-key or public
• way in which plaintext is processed
• block / stream
8. CRYPTANALYSIS
• objective to recover key not just message
• general approaches:
• cryptanalytic attack
• brute-force attack
9. CRYPTANALYTIC ATTACKS
• ciphertext only
• only know algorithm & ciphertext, is statistical, know or can identify plaintext
• known plaintext
• know/suspect plaintext & ciphertext
• chosen plaintext
• select plaintext and obtain ciphertext
• chosen ciphertext
• select ciphertext and obtain plaintext
• chosen text
• select plaintext or ciphertext to en/decrypt
10. MORE DEFINITIONS
• unconditional security
• no matter how much computer power or time is available, the cipher cannot be
broken since the ciphertext provides insufficient information to uniquely
determine the corresponding plaintext
• computational security
• given limited computing resources (eg time needed for calculations is greater
than age of universe), the cipher cannot be broken
11. BRUTE FORCE SEARCH
• always possible to simply try every key
• most basic attack, proportional to key size
• assume either know / recognise plaintext
Key Size (bits) Number of Alternative
Keys
Time required at 1
decryption/µs
Time required at 106
decryptions/µs
32 232 = 4.3 109 231 µs = 35.8 minutes 2.15 milliseconds
56 256 = 7.2 1016 255 µs = 1142 years 10.01 hours
128 2128 = 3.4 1038 2127 µs = 5.4 1024 years 5.4 1018 years
168 2168 = 3.7 1050 2167 µs = 5.9 1036 years 5.9 1030 years
26 characters
(permutation)
26! = 4 1026 2 1026 µs = 6.4 1012 years 6.4 106 years
12. CLASSICAL SUBSTITUTION
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 ciphertext bit patterns
13. CAESAR CIPHER
• earliest known substitution cipher
• by Julius Caesar
• first attested use in military affairs
• replaces each letter by 3rd letter on
• example:
meet me after the toga party
PHHW PH DIWHU WKH WRJD SDUWB
14. CAESAR CIPHER
• can define transformation as:
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
D E F G H I J K L M N O P Q R S T U V W X Y Z A B C
• 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
0 1 2 3 4 5 6 7 8 9 10 11 12 13 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)
15. CRYPTANALYSIS OF CAESAR
CIPHER
• only have 26 possible ciphers
• A maps to A,B,..Z
• could simply try each in turn
• a brute force search
• given ciphertext, just try all shifts of letters
• do need to recognize when have plaintext
• eg. break ciphertext "GCUA VQ DTGCM"
16. MONOALPHABETIC CIPHER
• rather than just shifting the alphabet
• could shuffle (jumble) the letters arbitrarily
• each plaintext letter maps to a different
random ciphertext letter
• hence key is 26 letters long
Plain: abcdefghijklmnopqrstuvwxyz
Cipher: DKVQFIBJWPESCXHTMYAUOLRGZN
Plaintext: ifwewishtoreplaceletters
Ciphertext: WIRFRWAJUHYFTSDVFSFUUFYA
17. MONOALPHABETIC CIPHER
SECURITY
• now have a total of 26! = 4 x 1026 keys
• with so many keys, might think is secure
• but would be !!!WRONG!!!
• problem is language characteristics
18. LANGUAGE REDUNDANCY
AND CRYPTANALYSIS
• human languages are redundant
• eg "th lrd s m shphrd shll nt wnt"
• letters are not equally commonly used
• in English E is by far the most common letter
• followed by T,R,N,I,O,A,S
• other letters like Z,J,K,Q,X are fairly rare
• have tables of single, double & triple letter
frequencies for various languages
20. USE IN CRYPTANALYSIS
• key concept - monoalphabetic substitution ciphers
do not change relative letter frequencies
• discovered by Arabian scientists in 9th century
• calculate letter frequencies for ciphertext
• compare counts/plots against known values
• if caesar cipher look for common peaks/troughs
• peaks at: A-E-I triple, NO pair, RST triple
• troughs at: JK, X-Z
• for monoalphabetic must identify each letter
• tables of common double/triple letters help
21. EXAMPLE CRYPTANALYSIS
• given ciphertext:
UZQSOVUOHXMOPVGPOZPEVSGZWSZOPFPESXUDBMETSXAIZ
VUEPHZHMDZSHZOWSFPAPPDTSVPQUZWYMXUZUHSX
EPYEPOPDZSZUFPOMBZWPFUPZHMDJUDTMOHMQ
• count relative letter frequencies (see text)
• guess P & Z are e and t
• guess ZW is th and hence ZWP is the
• proceeding with trial and error finally get:
it was disclosed yesterday that several informal
but
direct contacts have been made with political
representatives of the viet cong in moscow
22. PLAYFAIR CIPHER
• not even the large number of keys in a
monoalphabetic cipher provides security
• one approach to improving security was to encrypt
multiple letters
• the Playfair Cipher is an example
• invented by Charles Wheatstone in 1854, but named
after his friend Baron Playfair
23. PLAYFAIR KEY MATRIX
• a 5X5 matrix of letters based on a keyword
• fill in letters of keyword (sans duplicates)
• fill rest of matrix with other letters
• eg. 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
24. ENCRYPTING AND DECRYPTING
• plaintext is encrypted two letters at a time
1. if a pair is a repeated letter, insert filler like 'X’
2. if both letters fall in the same row, replace each with letter to right (wrapping back
to start from end)
3. if both letters fall in the same column, replace each with the letter below it (again
wrapping to top from bottom)
4. otherwise each letter is replaced by the letter in the same row and in the column
of the other letter of the pair
25. SECURITY OF PLAYFAIR CIPHER
• security much improved over
monoalphabetic
• since have 26 x 26 = 676 digrams
• would need a 676 entry frequency table
to analyse (verses 26 for a
monoalphabetic)
• and correspondingly more ciphertext
• was widely used for many years
• eg. by US & British military in WW1
• it can be broken, given a few hundred
letters
• since still has much of plaintext structure
26. POLYALPHABETIC CIPHERS
• polyalphabetic substitution ciphers
• improve security using multiple cipher alphabets
• make 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
27. VIGENÈRE CIPHER
• 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
28. EXAMPLE OF VIGENÈRE CIPHER
• write the plaintext out
• write the keyword repeated above it
• use each key letter as a caesar cipher key
• encrypt the corresponding plaintext letter
• eg using keyword deceptive
key: deceptivedeceptivedeceptive
plaintext: wearediscoveredsaveyourself
ciphertext:ZICVTWQNGRZGVTWAVZHCQYGLMGJ
29. AIDS
• simple aids can assist with en/decryption
• a Saint-Cyr Slide is a simple manual aid
• a slide with repeated alphabet
• line up plaintext 'A' with key letter, eg 'C'
• then read off any mapping for key letter
• can bend round into a cipher disk
• or expand into a Vigenère Tableau
30. SECURITY OF VIGENÈRE CIPHERS
• have multiple ciphertext letters for each plaintext letter
• hence letter frequencies are obscured
• but not totally lost
• start with letter frequencies
• see if look monoalphabetic or not
• if not, then need to determine number of alphabets,
since then can attach each
31. KASISKI METHOD
• method developed by Babbage / Kasiski
• repetitions in ciphertext give clues to period
• so find same plaintext an exact period apart
• which results in the same ciphertext
• of course, could also be random fluke
• eg repeated “VTW” in previous example
• suggests size of 3 or 9
• then attack each monoalphabetic cipher
individually using same techniques as before
32. AUTOKEY CIPHER
• ideally want a key as long as the message
• Vigenère proposed the autokey cipher
• with keyword is prefixed to message as key
• knowing keyword can recover the first few letters
• use these in turn on the rest of the message
• but still have frequency characteristics to attack
• eg. given key deceptive
key: deceptivewearediscoveredsav
plaintext: wearediscoveredsaveyourself
ciphertext:ZICVTWQNGKZEIIGASXSTSLVVWLA
33. ONE-TIME PAD
• if a truly random key as long as the message is used, the
cipher will be secure
• called a One-Time pad
• is unbreakable since ciphertext bears no statistical
relationship to the plaintext
• since for any plaintext & any ciphertext there exists a key
mapping one to other
• can only use the key once though
• problems in generation & safe distribution of key
34. 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
35. 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
36. ROW TRANSPOSITION CIPHERS
• a more complex transposition
• 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: 3 4 2 1 5 6 7
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
37. 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
38. ROTOR MACHINES
• before modern ciphers, rotor machines
were most common complex ciphers in
use
• 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 263=17576
alphabets
40. 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
41. SUMMARY
• have considered:
• classical cipher techniques and terminology
• monoalphabetic substitution ciphers
• cryptanalysis using letter frequencies
• Playfair cipher
• polyalphabetic ciphers
• transposition ciphers
• product ciphers and rotor machines
• stenography