Cryptocurrencies: an interactive blockchain course

Published 8 Nov 20266 min read

Cryptocurrencies is an interactive blockchain course that explains how cryptocurrencies such as Bitcoin actually work, without hype and without investment advice. Its 25 short sections cover money as a ledger, shared ledgers, hash functions, what is inside a block, mining and difficulty, keys, wallets and digital signatures, transactions, how the network agrees on one chain, proof of stake, smart contracts, keeping keys safe and spotting scams.

It opens with a four-block chain hashed with real SHA-256: edit one block and every block after it breaks, then mining repairs them one by one. That demo is the core idea of a blockchain.

What the course covers

Sections	Topic	What you do
1 to 4	A chain of blocks, money as a ledger, and one ledger with many copies	Work out a balance from a ledger of payments
5 to 8	Hash functions and what is inside a block	Predict whether two inputs share a hash, then find an edited block
9 to 12	Mining and difficulty	Work out the average number of tries, then check a miner's work
13 to 15	Keys, wallets and digital signatures	Match keys, addresses, signatures and seed phrases to their jobs
16 to 18	Transactions, the mempool and agreeing on one chain	Put the steps of a payment and of mining in order
19 to 20	Proof of stake	Sort statements into proof of work, proof of stake or both
21 to 22	Smart contracts and tokens	Say what each call to a small crowdfunding contract does
23 to 25	Keeping your keys safe, risks and scams	Spot red flags and safe habits

Ledgers and hashes

Money is really a ledger, a list of payments. A bank keeps one ledger you have to trust; a cryptocurrency keeps the same ledger on thousands of computers. Each block holds payments, the previous block's hash and a number called the nonce. A hash function such as SHA-256 turns any input into a fixed-length fingerprint, and changing even one character changes the hash completely, which is why editing an old block breaks every later one.

Mining, keys and agreement

In proof of work, a block only counts if its hash starts with enough zeros, so miners keep changing the nonce and hashing again. Each extra leading hex zero makes the search 16 times longer on average: 4 zeros take about 16⁴ = 65,536 tries. Spending needs a private key, which signs each payment; anyone can check the signature with the matching public key. Proof of stake replaces mining with deposits from validators.

Contracts and safety

Smart contracts are programs stored on a blockchain that run exactly as written. The course ends with the practical side: a seed phrase gives full control of a wallet, payments cannot be reversed, and scams are common. The UK Financial Conduct Authority warns about crypto investment scams, and the course treats spotting them as a core skill.

Try a question from the course

A balance is just the sum of a ledger. If Amy starts with 50 coins, pays Ben 20 and then receives 15 from Cal, her balance is 50 − 20 + 15 = 45. No coins are stored anywhere; the number comes entirely from the list of payments.

Now work out a balance from a new ledger, then press Mark to check your answer in the course.

Press Mark to have your answer marked in the Cryptocurrencies course.

Who this course is for

Curious learners who want to understand what a blockchain is beneath the headlines.
Computing students interested in hashing, public-key cryptography and distributed systems.
Anyone thinking about owning crypto, who should understand keys, irreversibility and scams first. The course gives no investment advice.

What you need to know first

Nothing formal. Knowing hexadecimal helps with hashes, and the Binary, Hexadecimal & Decimal course covers it. The calculations are additions and powers of 16.

How long it takes

There are 25 sections and most take a few minutes. Learners without a plan can open two sections of a course a day, in order, so the whole course takes 13 days. A plan removes the daily limit and lets you go straight to any topic, such as smart contracts.

Guided courseQuantum ComputingWhat future quantum computers could mean for the cryptography that blockchains rely on.

Common questions

Is this blockchain course free?

You can take every section without paying, two sections a day, in order. A plan removes the daily limit and opens any section straight away.

How does a blockchain work?

It is a ledger split into blocks, where each block includes the hash of the one before. Many computers keep copies and agree on new blocks, so changing an old block would break every later one and be rejected.

What is Bitcoin mining?

Repeatedly changing a number in a block and hashing it until the hash starts with enough zeros. The first miner to find one adds the block and is rewarded. The difficulty adjusts so blocks keep coming at a steady pace.

What is the difference between proof of work and proof of stake?

Proof of work secures the chain with computing effort spent on mining. Proof of stake secures it with coins that validators lock up as a deposit, which they can lose if they cheat.

What is a private key?

A secret number that lets you sign payments from your wallet. Anyone with your private key or seed phrase can take your coins, so it must never be shared.

Does the course tell me what to invest in?

No. It explains how cryptocurrencies work and how to avoid common scams. It gives no financial or investment advice.

Revision cards

Say the answer first, then flip the card to check it.

Where to go next

Learn it
Cryptocurrencies
Blockchain, Bitcoin and the tech reshaping money, from hashing to smart contracts
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