Applied Cryptography - Algorithms and GPA Calculation

Applied Cryptography

• 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.

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.