Introduction to Cryptography

Cryptography

• Cryptography is the science of encrypting and decrypting written communication
• It is derived from the Greek words "kryptos" (hidden) and "graphia" (writing)
• It protects sensitive information during storage or transmission across networks
• Modern cryptography is often associated with electronic communications like passwords, logins, and ATM security

Goals of Cryptography

• Privacy: Protecting sensitive information from unauthorized access
• Data Integrity: Ensuring that data has not been altered during transmission
• Authentication: Verifying the identity of the sender or receiver

History of Cryptography

• Cryptography's history spans thousands of years
• The Enigma machines, electro-mechanical rotor cipher machines, were used in the 20th century for diplomatic and military communication
• Early forms of cryptography include the Scytale, a method used by the Spartans, involving wrapping a message around a wooden rod

Encryption and Decryption

• Encryption: Transforming data using an algorithm to make it unreadable without a key
• Decryption: Converting encrypted data back to its original form using the corresponding key

Ciphers

• Cipher: An algorithm for performing encryption or decryption, often depending on a key
• Substitution Cipher: Replaces units of plaintext with ciphertext based on a systematic rule
• Monoalphabetic Cipher: A substitution cipher where each letter is replaced by a different letter
  • Caesar Cipher: A simple substitution cipher shifting each letter a fixed number of positions in the alphabet
  • Atbash Cipher: A substitution cipher replacing each letter with its opposite letter in the alphabet
  • Affine Cipher: A substitution cipher which depends on two parameters for the letter substitutions
  • ROT13 Cipher: A specific Affine Cipher

Transposition Ciphers

• Replaces the order of characters in a message
• Rail Fence Cipher: Arranges characters in a series of rows and reads them down the columns
• Route Cipher: Uses a pattern to determine which character to read in the transposition
• Columnar Transposition: Arranges the plaintext into columns and reads in a specific sequence, sometimes using a keyword to create the column order
• Keyword Columnar Cipher: A more complex method where the keyword determines the order of columns

Modular Codes

• Based on modular arithmetic
• Encodes and decodes a message using a defined key and modular math to create a code
• The decoding key is the inverse of the encoding key.

Explore the fundamentals of cryptography, its goals, and historical developments. This quiz covers essential concepts like privacy, data integrity, and authentication, as well as notable instances such as the Enigma machine and ancient methods like the Scytale. Test your knowledge on the science of securing communication.