Module 1: Blockchain Foundations

The Problem Blockchain Solves

Before you can judge any cryptocurrency or blockchain project, you need to understand the specific problem the technology was designed to solve. Many projects use the word "blockchain" for things a normal database does better. Knowing the original problem helps you separate genuine uses from marketing, and it explains why blockchains are built the way they are, including their slowness and cost compared with ordinary systems.

Money and records need trust

Whenever you send money digitally, someone keeps the record. When you send KES 2,000 by M-Pesa, the mobile money provider updates its records: your balance goes down and the recipient's goes up. When you pay by bank transfer, the banks update their ledgers and settle with each other. You trust these organisations to keep accurate records, to stop you spending the same money twice, and to follow the law.

This model works well most of the time. But it depends on central intermediaries, and that brings some limitations:

• The intermediary can make mistakes, be hacked, or go out of business.
• It can freeze or reverse transactions, which protects consumers but also gives it control.
• Cross-border payments often pass through several intermediaries, adding cost and delay.
• People without access to banks or accepted identification may be excluded.

The double-spending problem

Digital information is easy to copy. If a digital coin were just a file, you could send the same file to two people. With a central record keeper, this is solved easily: the keeper checks your balance. The challenge that Bitcoin addressed in 2008 and 2009 was how to prevent double spending without a central keeper, among participants who do not know or trust each other.

The answer combined several existing ideas:

1. A shared public ledger: every participant can hold a copy of the full transaction history.
2. Cryptographic signatures: only the holder of a private key can authorise spending from an address.
3. Chained blocks of transactions: changing past records would require redoing work for every later block.
4. A consensus mechanism: rules that let thousands of computers agree on which version of the ledger is valid, with economic incentives to follow the rules.

The result is a system where trust is placed in open rules, mathematics and incentives rather than in one organisation.

When a blockchain makes sense, and when it does not

Blockchains trade efficiency for independence from a central party. A useful test is to ask these questions:

• Do several parties who do not fully trust each other need to share the same records?
• Is there no single party that everyone is willing to trust to keep those records?
• Do the records need to be very hard to alter after the fact?
• Is the benefit worth slower processing and higher cost than a normal database?

If one organisation controls the data anyway, an ordinary database is usually cheaper, faster and easier to fix when mistakes happen.

Worked example: two proposals

Imagine you sit on the board of a hypothetical Nairobi savings group, and two members bring proposals.

Proposal 1: "Let's put our member contribution records on a blockchain." The group already has a treasurer, the records are only used internally, and members trust the committee. A shared spreadsheet with regular reconciliation and two signatories would meet the need at almost no cost. A blockchain adds complexity without solving a real problem.

Proposal 2: A member who works in export logistics describes a network of farmers, transporters, warehouses and foreign buyers who each keep separate records of the same shipments and argue about discrepancies. No party wants another to control the master record. Here a shared ledger, possibly a permissioned blockchain where only known participants can write, may genuinely reduce disputes. It still needs careful evaluation of cost and adoption, but it passes the basic tests.

Common mistakes to avoid

• Assuming blockchain means truth. A blockchain records what is entered. If false information goes in, it is preserved permanently.
• Confusing blockchain with cryptocurrency. Cryptocurrencies use blockchains, but not every blockchain use needs a tradable coin.
• Believing "decentralised" is always true. Many projects are controlled by a small team despite the label. You will learn to check this later in the course.
• Ignoring trade-offs. Independence from intermediaries also means fewer protections when things go wrong, such as no one to reverse a mistaken payment.