Fundamentals 6: Introduction to Cryptography

by Arnav Vora

Cryptography is the process of hiding information or communicating securely in an environment where everyone is trying to read the communication. Most cryptography examples involve Alice and Bob trying to communicate while Eve listens in. Today, we explored the basics of cryptography, starting with the most fundamental classical ciphers used before we had powerful computers. However, these ciphers are completely inadequate to hide data in today's age. We learn of ways that computers can break these ciphers, and then move to discussing more modern forms of encryption. A fundamental operation in modern cryptography is XOR. This can be used to create the One-time Pad, a mathematically perfectly secure cipher that reveals no information about the information being sent. However, this cipher isn't practical in most scenarios, and it has many conditions for it to actually achieve perfect security. We then discuss two main classes of symmetric ciphers that are widely used: block ciphers and stream ciphers.

Slides

Challenges

The following challenges in increasing difficulty are deployed to platform.acmcyber.com to practice the concepts covered in the slides.

  • Challenge 1 - fundamentals/Caesar turns 47
  • Challenge 2 - fundamentals/vigenere is kill
  • Challenge 3 - fundamentals/XOR practice
  • Challenge 4 - fundamentals/Practice Run
  • Challenge 5 - fundamentals/Practice Run 2
  • Challenge 6 - fundamentals/bigram

Resources

The following resources are great to practice/learn about the ciphers covered in the slides.

  • dcode.fr: This website hosts many classical ciphers, and provides tools for encryption, decryption, and automatic cracking of ciphers. This is a staple for classical cryptography challenges.
  • guballa Substitution Solver: My personal favorite website to crack monoalphabetic substitution ciphers.
  • Cyberchef: This website also hosts many ciphers, and provides tools for encryption, decryption, and automatic cracking. It is very powerful at detecting the cipher used in encryption if is unknown, and is also a staple for classical cryptography challenges.
  • pycryptodome: A library that implements many modern-day cryptographic algorithms.