Bits, bytes and encodings
How text and numbers become bytes, what hex and Base64 are for, and why encoding hides nothing.
Cryptography basics
Everything you need before the lattice chapters, explained from zero.
These seven short chapters cover the building blocks every developer meets: encoding, hashing, encryption, message authentication, key exchange and signatures. Each one starts from an everyday picture, then gives the precise idea, a small example you can check, working code, and the mistakes that cause real bugs. The interactive demos run real cryptography in your browser through the Web Crypto API, so nothing you type leaves your machine.
The last chapter explains what quantum computers change and leads straight into 1.1 What is a lattice? If a symbol is unfamiliar, the math reference explains it.
Hash functions
Fixed-size fingerprints of any data: the three security properties, the avalanche effect and the birthday bound.
Symmetric encryption
One shared key: the one-time pad, AES, nonces, and why modern encryption is always authenticated.
MACs, key derivation and randomness
Proving a message was not changed, turning secrets into keys, storing passwords, and getting good random numbers.
Public-key cryptography and key exchange
How two strangers agree on a secret: Diffie–Hellman, RSA and elliptic curves, with numbers you can check by hand.
Digital signatures and certificates
Signing and verifying, Ed25519 and ECDSA, and how certificates let your browser trust a website.
Quantum computers and KEMs
What a quantum computer would break, what it would not, and why the new standards are built on lattices.