Cryptography

Cryptography is the science and practice of securing communication and information through the use of codes, so that only the intended recipients can read and process it. As a fundamental pillar of both computer science and cybersecurity, it employs mathematical algorithms and keys to perform encryption (converting readable plaintext into unreadable ciphertext) and decryption (reversing the process). Modern cryptography goes beyond mere secrecy to provide essential security services such as data integrity, ensuring information is unaltered; authentication, verifying the identity of users; and non-repudiation, preventing senders from denying they sent a message, thereby protecting everything from private emails to financial transactions.

1. Foundations of Cryptography
   1. Core Concepts and Terminology
      1. Cryptography
      2. Cryptanalysis
      3. Cryptology
      4. Plaintext
      5. Ciphertext
      6. Keys
         1. Secret Keys
         2. Public Keys
         3. Private Keys
         4. Key Space
         5. Key Length
      7. Encryption
      8. Decryption
      9. Ciphers
         1. Definition of a Cipher
         2. Cipher vs. Code Distinction
      10. Algorithm vs. Key Distinction
      11. Kerckhoffs's Principle
      12. Security by Obscurity vs. Open Design
      13. Computational Security vs. Information-Theoretic Security
   2. Historical Context and Evolution
      1. Ancient Cryptography
         1. Scytale
         2. Atbash Cipher
         3. Polybius Square
      2. Medieval and Renaissance Cryptography
         1. Alberti Cipher Disk
         2. Trithemius Tabula Recta
      3. Modern Era Developments
         1. Telegraph and Communication Security
         2. World War Cryptography
         3. Computer Age Cryptography
   3. Classical Cryptography
      1. Substitution Ciphers
         1. Monoalphabetic Substitution
            1. Caesar Cipher
               1. Algorithm Description
               2. Mathematical Representation
               3. Security Analysis
               4. Brute Force Vulnerability
            2. Simple Substitution Cipher
               1. Keyspace Analysis
               2. Frequency Analysis Vulnerability
               3. Pattern Recognition Attacks
            3. Affine Cipher
               1. Mathematical Foundation
               2. Encryption and Decryption
               3. Key Requirements
         2. Polyalphabetic Substitution
            1. Vigenère Cipher
               1. Encryption Process
               2. Decryption Process
               3. Key Repetition Problem
               4. Kasiski Examination
               5. Index of Coincidence Attack
            2. Beaufort Cipher
            3. Autokey Cipher
            4. Running Key Cipher
      2. Transposition Ciphers
         1. Simple Transposition
            1. Rail Fence Cipher
               1. Encryption Process
               2. Decryption Process
               3. Security Limitations
            2. Route Cipher
         2. Columnar Transposition
            1. Simple Columnar Transposition
            2. Keyed Columnar Transposition
            3. Double Transposition
         3. Block Transposition
      3. Combination Ciphers
         1. Substitution-Transposition Combinations
         2. Fractionating Ciphers
            1. Playfair Cipher
            2. Four-Square Cipher
            3. Two-Square Cipher
      4. Mechanical and Electromechanical Systems
         1. Cipher Wheels and Disks
         2. Rotor Machines
            1. Enigma Machine
               1. Rotor Mechanism
               2. Plugboard Configuration
               3. Daily Key Settings
               4. Cryptanalysis Methods
               5. Historical Impact
            2. Lorenz Cipher Machine
               1. Teleprinter Encryption
               2. Wheel Patterns
               3. Colossus Computer
            3. Purple Machine
            4. SIGABA
   4. Fundamental Security Goals
      1. Confidentiality
         1. Data Confidentiality
         2. Privacy Protection
         3. Information Hiding
      2. Integrity
         1. Data Integrity
         2. Message Integrity
         3. System Integrity
      3. Authentication
         1. Entity Authentication
         2. Data Origin Authentication
         3. Message Authentication
      4. Non-repudiation
         1. Digital Evidence
         2. Proof of Origin
         3. Proof of Delivery
      5. Availability
         1. System Availability
         2. Data Availability
         3. Service Continuity
      6. Authorization
         1. Access Control
         2. Permission Management
      7. Accountability
         1. Audit Trails
         2. Logging and Monitoring
      8. Security Goal Relationships
         1. Interdependencies
         2. Trade-offs
         3. Balanced Security Design
   5. Threat Models and Attack Classifications
      1. Passive Attacks
         1. Eavesdropping
         2. Traffic Analysis
         3. Cryptanalysis
      2. Active Attacks
         1. Masquerade
         2. Replay
         3. Message Modification
         4. Denial of Service
      3. Insider vs. Outsider Threats
      4. Computational vs. Information-Theoretic Attacks