STEMming for you · 4th Edition
How the digital world keeps secrets and decides what to trust — starting with how the internet actually works, building through hashing and cryptography, and finishing with digital signatures, blockchain and the padlock in your browser.
This edition followed a single thread — trust on the internet — from the ground up. It began with how data really travels the network, used biometrics and password storage to motivate hashing, then built the mathematics of cryptography from the Caesar cipher all the way to RSA and elliptic curves. The final sessions tied it together: digital signatures, cryptocurrency and blockchain, and how HTTPS certificates keep the web secure. Throughout, students worked hands-on — breaking ciphers, generating their own RSA keys, and building a small blockchain.
Using the example of streaming a video, explained that data is bits stored on servers in data centres connected by undersea cables and satellites, and that devices communicate using protocols — shared sets of rules. Previewed the key protocols (IP, TCP, DNS, HTTPS) to be explored later.
Covered bits and bytes and the kilo/Mega/Giga/Tera prefixes as powers of two, then introduced biometrics — recognising people by unique traits — comparing fingerprints, DNA, iris and facial features, and introduced hashing as a one-way function for storing sensitive data safely.
Worked through fingerprint-minutiae probabilities and the iris-vs-retina distinction, then explored hash functions (low collision rate, avalanche effect) hands-on with SHA-256, demonstrating dictionary attacks and a client–server–hacker role-play to show why passwords must be unique.
Introduced cryptography and symmetric (secret-key) encryption via the Caesar cipher — and how easily it breaks — referencing the Enigma machine. Students broke ciphers in sender/receiver/hacker groups, ending with the leap to public-key cryptography and RSA.
Explained why securely sharing a secret key over a network is the core problem, motivating RSA, then worked a concrete encrypt/decrypt example and taught key generation step by step (primes, modulus, Euler's totient, choosing e and d) — with students creating and using their own key pairs.
Explored why RSA is secure — breaking it means factoring huge numbers, which would take longer than the age of the universe — and how Shor's algorithm on a quantum computer threatens that. Introduced Diffie–Hellman and elliptic-curve cryptography.
Described elliptic-curve cryptography and then digital signatures: hashing a document and encrypting the hash with a private key so anyone can verify it with the public key — contrasted with the weaknesses of handwritten signatures, with a hands-on RSA signing exercise.
Examined the problems with traditional currency and how digital money relies on trusted banks keeping accurate ledgers, then introduced the blockchain as a decentralised ledger made tamper-resistant by chaining blocks via hashes — with students building a small blockchain using an online SHA-256 tool.
Introduced digital certificates that bind a public key to a subject and are vouched for by a trusted issuer, then walked through how HTTPS works end to end — DNS lookup, certificate verification against trusted roots, and the TLS handshake that securely exchanges a symmetric session key.
