In today's interconnected world, information is the most valuable asset. Cryptography is the science that ensures this information remains private, authentic, and untampered with. This guide covers everything from fundamental principles to modern-day applications. 1. What is Cryptography? Cryptography (from the Greek words kryptos meaning hidden and graphein meaning writing) is the practice of securing communication through mathematical techniques. The main goal is to convert Plaintext (readable information) into Ciphertext (unreadable scrambled data) so that only those with the correct "key" can read it. 2. The Core Pillars (CIA Triad + 1) Cryptography serves four primary functions: Confidentiality: Only the intended recipient can read the message. Integrity: The message cannot be altered during transit without being detected. Authentication: Proving the identity of the sender. Non-repudiation: The sender cannot deny having sent the message later. 3. Types of Cr...