Cryptography
From classical ciphers to AES, hashes, RSA, Diffie–Hellman, certificates and TLS, and the practical mistakes that break real systems.
Course · 8 lessons · 61 min
- 1Classical ciphers and why they failFreeShift, substitution and Vigenère ciphers, the statistics that break them, Kerckhoffs's principle and the one cipher that is provably unbreakable.1883–1949 · 7 min
- 2Modular arithmetic for cryptographyCongruences, inverses with the extended Euclidean algorithm, Fermat and Euler, and fast exponentiation: the arithmetic that public-key cryptography runs on.1640–1801 · 7 min
- 3Symmetric encryption: AES and modes of operationHow AES was chosen and what a round does, why a block cipher needs a mode, why ECB leaks, and how CBC, CTR and GCM use IVs and nonces safely.1997–2007 · 8 min
- 4Hash functions and message authentication codesThe three security properties of a hash, the birthday bound, why SHA-1 is dead, length extension, and how HMAC turns a hash into a keyed integrity check.1995–2017 · 7 min
- 5Public-key cryptography: Diffie–Hellman and RSAHow two strangers agree a key in public, how RSA keys are built and why decryption works, with both worked by hand on small numbers.1973–1978 · 8 min
- 6Digital signatures, certificates and PKIHash-then-sign, the signature schemes in FIPS 186-5, what an X.509 certificate binds, how a chain is validated and what Certificate Transparency adds.2008–2023 · 8 min
- 7TLS at the protocol levelThe TLS 1.3 handshake message by message, the key schedule, the AEAD record layer, 0-RTT and its replay risk, and why old versions were retired.2014–2021 · 8 min
- 8Practical pitfalls: randomness, keys, passwords and post-quantumWhere real cryptography breaks: weak randomness, poor key management, fast password hashes, and the migration to NIST's 2024 post-quantum standards.2008–2024 · 8 min