Cryptography, explained

From the Caesar cipher to AES and RSA: how ciphers work, how they are broken, and how to use them – with examples, code and tools you can try online.

Sections

Theory

Kerckhoffs’s principle, modular arithmetic, block cipher modes, MAC, one-way functions and more.
Simple ciphers

Classical ciphers you can do by hand: Caesar, Playfair, Vigenère, transposition, Enigma.
Symmetric ciphers

Stream and block ciphers: OTP, RC4, Salsa20, DES, AES, Blowfish, Camellia.
Asymmetric ciphers

Public-key cryptography: Merkle’s puzzles, Diffie–Hellman, RSA.
Attacks

Brute force, frequency analysis, man-in-the-middle, replay, KRACK and other attacks.
Software

Cryptography in practice: JCA/JCE, security tokens, key-based authentication, Docker.