This post documents my personal journey of learning cryptography. I’ve curated and organized the exact resources, videos, and concepts I used—starting from foundational math to public key cryptography. If you’re someone starting out or struggling with the core ideas, this learning path might give you the clarity and structure you need.

1. Cryptography Fundamentals

First, I built my foundation with these resources:

• ChatGPT Thread for Introduction to Cryptography → Read this to kickstart.

2. Cryptography Basics

These videos helped me understand core concepts:

• Crypto Basics Part 1
  

• Crypto Basics Part 2
  

• For Cryptography Mathematics (including Modular Arithmetic, Prime Numbers, GCD, Euler’s Totient Functions or Theorems, Fermat’s Theorems, Groups, Fields and etc.) Just go and Watch Cryptography Mathematics Playlist →

3.0 RSA Prerequisites (Math Fundamentals)

Modular Exponentiation

When an exponent is very large, you cannot calculate (a^b) directly, so you apply modular arithmetic shortcuts. The method you choose depends on the type of modulus and numbers involved.

1. If nothing special → use Fast Modular Exponentiation.
2. If modulus is prime → use Fermat’s Little Theorem to reduce exponent.
3. If modulus non-prime but gcd(a, m) = 1 → use Euler’s Totient to reduce exponent.
4. If modulus is composite and factorable → use CRT to break and recombine.
5. If exponent is a power tower → reduce exponent first, then compute using fast mod exponentiation.

ChatGPT Thread for Modular Exponentiation → For better understaind:

• Only video you may need:

Now, extra videos for more clarity:

• Fast Modular Exponentiation Part 1
• Fast Modular Exponentiation Part 2

3.1 Public Key Cryptography

Understanding public/private keys:

• Public Key Cryptography Explained
  

Diffie-Hellman & RSA

Just trust me, and watch the full playlist below:
Watch Complete RSA Playlist →

To calculate any of `e` or `d` if any of them is given, let's say `e` is given but not `d` or vice versa, also we know φ(n) then ChatGPT Thread for e or d calculation →

Symmetric Cryptography

Fiestel Cipher

Modes of Operation

DES

Galois Field

AES

the following video is must watch:

This learning path helped me build a solid understanding of these complex cryptographic concepts. I hope it can help others too!