cryptography
7 free lessons tagged cryptography across Science, Programming. Each one is a short sequence of focused steps with narration and a five-question quiz at the end — take them in any order, no signup required.
Why Nobody Deploys It: The Gap Between Proof and Product
QKD has an unconditional security proof and almost no deployment. This lesson covers the authentication bootstrap it cannot solve, distance limits and the trusted node compromise, attacks on real hardware that the proof does not cover, why NSA and NCSC recommend against it, and where quantum genuinely delivers.
Quantum Key Distribution: BB84 and Why Eavesdropping Shows
Quantum cryptography uses physics rather than computational hardness. This lesson covers the no-cloning theorem, the BB84 protocol step by step, why measurement in the wrong basis leaves a detectable trace, the error rate threshold, and the entanglement-based alternative.
Post-quantum cryptography: lattices, codes, and the migration
What cryptographic schemes Shor's algorithm threatens, what post-quantum schemes replace them, the math behind lattice-based cryptography, the NIST standardization process and its outputs, and the operational mechanics of a real-world cryptographic migration.
Symmetric Ciphers and Modes of Operation
AES and block ciphers are primitive building blocks, not complete encryption schemes. Learn how ECB leaks structure, why CBC and CTR modes work differently, and why GCM is the modern default — including the catastrophic consequences of nonce reuse.
Public-Key Cryptography: RSA and ECC
Trapdoor functions power every TLS handshake, code signature, and SSH session. Master RSA key generation and its math, why textbook RSA is trivially broken, what elliptic curves add, and how ECDSA and Ed25519 compare — with key-size equivalences you can quote in code reviews.
Key Exchange and TLS 1.3
Every HTTPS connection negotiates a fresh secret over an untrusted network. Learn Diffie-Hellman and ECDH from first principles, why forward secrecy matters when private keys leak, how TLS 1.3 cut the handshake to one round-trip, and how certificate chains stop man-in-the-middle attacks.
Hash Functions, MACs, and Password Hashing
Hash functions are not all equal and MACs are not just hashes with a secret. Learn the three resistance properties, why length-extension attacks break naive HMAC constructions, how KDFs differ from hashes, and why bcrypt/scrypt/Argon2 exist for passwords.