Applied Cryptography

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Questions and Answers

Which of the following best describes an algorithm?

A set of vague instructions that may not lead to a solution

A collection of unambiguous operations that produces a result and halts in finite time (correct)

A random sequence of numbers

An artistic expression of methods

Cryptanalysis focuses on the creation of ciphers to secure information.

False

What is the plaintext in cryptography?

Ordinary information before encryption

The process of converting ordinary information into unintelligible text is called ___.

encryption Signup and view all the answers

Match the cryptology terms with their definitions:

Cryptography = The science of using codes to secure information Cryptanalysis = The process of deciphering encoded messages Ciphertext = The result of encoding a plaintext message Plaintext = The original readable message before encoding Signup and view all the answers

What is the primary purpose of a cryptanalyst?

To break cipher text messages Signup and view all the answers

In a substitution cipher, the order of plaintext letters is preserved.

True Signup and view all the answers

What process is used to produce ciphertext from plaintext?

Encryption Signup and view all the answers

The process of converting ciphertext back to plaintext is called __________.

Decryption Signup and view all the answers

Match the following cryptographic terms with their definitions:

Plaintext = The original unencrypted message Ciphertext = The encrypted text Key = Information used in cipher known only to sender/receiver Transposition Cipher = Rearranges the characters within the text Signup and view all the answers

Which of the following ciphers is an example of a polyalphabetic cipher?

Vigenère Cipher Signup and view all the answers

The Playfair Cipher encrypts letters based solely on their order in the alphabet.

False Signup and view all the answers

What is the key generated from the keyword 'BLUSH' for the plaintext 'DAYLIGHT'?

BLUSHBLU Signup and view all the answers

In a Vigenère Cipher, the first letter of the plaintext and the key are used to determine the ciphertext using the __________.

Vigenère square Signup and view all the answers

Match the following terms with their definitions:

Substitution Cipher = A cipher where each letter is replaced by another letter. Polyalphabetic Cipher = A cipher using multiple substitution alphabets. Playfair Cipher = A cipher that encrypts pairs of letters. Vigenère Cipher = A specific type of polyalphabetic cipher using a keyword. Signup and view all the answers

What is the main characteristic of the Playfair Cipher?

It treats digraphs as single units for encryption. Signup and view all the answers

In the Playfair Cipher, if both letters of a pair are in the same row, you move to the left to encrypt them.

False Signup and view all the answers

What is done if the plaintext contains an odd number of letters when using the Playfair Cipher?

A Z is added to the last letter. Signup and view all the answers

The Playfair Cipher constructs a 5x5 matrix using a key and the letters of the alphabet, with 'I' and 'J' placed in the same _____.

box Signup and view all the answers

Match the following elements of the Playfair Cipher with their descriptions:

Key Square = A 5x5 matrix of letters used for encryption Digraphs = Pairs of letters from the plaintext Bogus Letter = A letter added to break up identical letters in a pair Plaintext = The original message before encryption Signup and view all the answers

Study Notes

This course is an introduction to cryptography and security algorithms.
The instructor is Jevah Rea Montas.
The course is GEC Elect 214 – Living in the IT Era.

Algorithm

An algorithm is a well-ordered set of unambiguous and effectively computable operations that produce a result and halt within a finite amount of time.
Examples include recipes, instructions for assembling objects, directions, makeup tutorials, teardown instructions, and repair guides.
A step-by-step example of an algorithm is provided for shampooing hair.

Algorithm for Calculating GPA

An algorithm is provided for calculating Grade Point Average (GPA).
The algorithm involves initializing variables like total_gp and course_count to zero.
It repeats steps for calculating total grade points for each course.
The algorithm then calculates GPA by dividing total_gp by course_count.
The value of GPA is printed at the end.

Why Algorithms are Important

Algorithms are crucial for automating problem-solving.
Specifying an algorithm for a problem allows for automation of its solution.
Discovering an algorithm enables the use of computing agents to solve problems.

Cryptography

Cryptography is the art of achieving security by encoding messages to make them unreadable.
It's the study of principles and techniques for hiding information within a cipher.
Cryptography converts ordinary information (plaintext) into unreadable text (ciphertext).

Fundamentals of Cryptography - Terminology

Cryptology is the science of encryption, encompassing both cryptography and cryptanalysis.
Cryptography is the process of creating and using codes to transmit information securely.
Cryptanalysis is the process of obtaining the plaintext message from a ciphertext message without the encryption keys.
Cryptanalyst is a person trying to break a ciphertext to get the original plaintext message.
Cipher is an encryption method combining the algorithm, key(s), and procedures for encryption and decryption.
Encryption (or enciphering) uses a key to convert plaintext to ciphertext.
Decryption (or deciphering) uses a key to convert ciphertext back to plaintext.
Key is the information known only to the sender and receiver used in the cipher.

Cryptographic Algorithms - 3 Dimensions

These are methods for classifying and categorizing cryptographic systems.
Type of operation includes transposition and substitution.
Number of keys used, such as 1, 2, or 3.
Way of processing plaintext, including block and stream ciphers.

Cryptographic Algorithms - According to Type of Operation Used

Substitution (Confusion): Replaces characters with other characters, preserving plaintext order.
Transposition (Diffusion): Rearranges characters within the text.

Cryptographic Algorithms - Substitution (Confusion) kinds

Monoalphabetic Cipher: A simple substitution cipher with a fixed replacement structure and is vulnerable due to fixed frequency analysis; example: Caesar Cipher.

Cryptographic Algorithms - Substitution (Confusion) example

Caesar Cipher: The earliest and simplest substitution cipher, shifting each letter a fixed number of positions down the alphabet.
Playfair Cipher: A multiple-letter substitution encryption cipher using a 5x5 matrix of letters based on a keyword. The input is two letters at a time

Playfair Cipher - Setup

The key (keyword) is written at the top of a 5x5 matrix.
The rest of the matrix is filled with the remaining alphabet, except "I" and "J" are treated as the same letter.

Playfair Cipher - Encryption Rules

If both letters are in the same row, take the letters to the right of each one (wrapping around if necessary).
If both letters are in the same column, take the letter below each one (wrapping if necessary).
If the letters are not in the same row or column, form a rectangle with the two letters, and take the letters on the opposite corners of the rectangle.

Vigenère Cipher

A polyalphabetic substitution cipher based on multiple substitution alphabets.
The algorithm relies on using a keyword repeatedly for encrypting characters.
An example is provided for generating keys based on keywords.

Vigenère Cipher (Encryption/Decryption)

Describes the process of encryption and decryption using a Vigenère square.
The process involves using a keyword to determine which substitution alphabet is used for each letter.

Transposition (Diffusion) example

Rail Fence Technique: An encryption technique where the message is written in a zigzag pattern across a series of “rails” and then combined to form the ciphertext.
Simple Columnar Transposition: Encrypts plaintext in rows, and then reads the ciphertext in columns, using a predetermined column order.

Activity: Caesar Cipher

The provided exercise details creating a program for encrypting and decrypting messages using a Caesar Cipher, providing specific functionalities and output requirements.

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Description

This quiz covers key concepts in applied cryptography, focusing on security algorithms and their applications. It also addresses the importance of algorithms in various contexts, including a specific algorithm for calculating GPA. Test your understanding of these crucial topics in the IT era.

Applied Cryptography - Algorithms and GPA Calculation

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