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Cryptography & Network Security
How secrets stay secret on the internet: classical ciphers, AES, RSA, key exchange and hashing — the maths behind the padlock in your browser.
Caesar & Vigenère Ciphers
The two classic shift ciphers. Caesar moves every letter by the same amount; Vigenère uses a key word to give every letter its own shift.
Playfair Cipher
A 5×5 square built from a key word encrypts two letters at a time, using three simple rules for rows, columns and rectangles.
AES (Advanced Encryption Standard)
The cipher that protects almost everything online. A 4×4 grid of bytes goes through 10 rounds of SubBytes, ShiftRows, MixColumns and AddRoundKey.
RSA Algorithm
Public-key encryption from two primes. Anyone can lock a message with the public key (e, n); only the private key (d, n) unlocks it.
Diffie–Hellman Key Exchange
Two strangers agree on a shared secret while an eavesdropper hears everything. Each mixes a public number with a private one, and both end up with gᵃᵇ mod p.
SHA-256 Hash Function
Any input becomes a 256-bit fingerprint. Padding, a message schedule and 64 rounds of mixing make every output bit depend on every input bit.
About Cryptography & Network Security
Every padlock in your browser rests on a few beautiful ideas. Turn a cipher wheel to see why Caesar falls to brute force and how Vigenère hides letter counts, fill a Playfair square, and watch a 4×4 AES state go through SubBytes, ShiftRows, MixColumns and AddRoundKey. Generate an RSA key pair from two primes, agree on a shared secret with Diffie–Hellman while an eavesdropper watches, and see one changed letter scramble a whole SHA-256 hash. Every lesson works through exam-style examples with real numbers.