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Women Who Code Workshop on Blockchain and Cryptocurrency
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Welcome to the Portland Women Who Code: Bitcoin, Cryptocurrency and Blockchain Workshop.

For this exercise we will be implementing a simple Blockchain from scratch. We will build a simple Blockchain with the goal of understanding what the basic features are that make up a blockchain.


The following exercise assumes you have a text editor installed and are able to write code in a language of your choice, but the solutions are written in Python and you can reference this blog on creating a Blockchain with a similar exercise that has solutions written in JavaScript. Feel free to pair with others while working through this exercise.

Feel free to either clone this repo to your local environment or simply reference the, and files that offer an example template for each of the exercises in the steps below.

Step 1 - What is a Block in a Blockchain?

In the presentation we learned that a Blockchain is a database, which is just a grouping of data organized in a particular way. A blockchain database organizes its data in blocks.

A block is a container data structure that permanently stores data that cannot be altered or removed.

Task: Implement a Block class.

Implement a Block class with the following attributes:

  • timestamp
  • hash of the previous block
  • transactional data

Step 2 - Lets Chain the Blocks Together

The Blockchain data strucutre is an ordered list of blocks. Blocks are linked "back", each pointing to the previous block in the chain. This creates an immutable data structure that is very difficult to alter maliciously.

Task: Implement a Blockchain class.

A Blockchain should have the following attributes:

  • a data structure to store blocks
  • the first block should be hardcoded, its called the genesis block

A genesis block is the first block of a block chain. The genesis block is typically hardcoded into the blockchain.

A Blockchain should be able to perform the following functions:

  • create a new block and add it to the blocks attribute
  • get the most recent block in from the blocks attribute
  • hash any blocks data. Since the concept of hashin is outside of the scope of this workshop, this function is provided for you. If you are interested in reading more about hash functions here is a little extra info...

A hash function is a way to turn any amount of data or any size data into a constant size. The values returned by a hash function are called hash values, hash codes, digests, or simply hashes. One example of a use case is a data structure called a hash table, used for rapid data lookup.

In the hash function provided, you can see that we are hashing the previous blocks hash. This is an important topic, but also pretty detailed so we don't want to go into the details here. If you are interested in diving deeper to understand this, see the resources listed at the bottom of this readme. However at a high level, hashing the blocks provides a secure mechanism to confirm the integrity of the Blockchain data.

Step 3 - Validate a Block

Task: Implement a validate_block method in the Blockchain class.

When we add a new block to the blockchain, check to make sure that the previous block hash still matches the current block's attribute that stores the hash of the previous block.

Implement a validation function that check that a block is valid. A block is valid when:

  • the previous hash attribute of the current block matches the current hash of the previous block


Now that you have a Block and Blockchain class, feel free to play around with the code and create your own blockchain! What kind of data would you store in your blockchain? See the solutions/ for an example of putting this code to use.

Beyond the workshop:

Topics not convered in this workshop that you may want to explore outside of this workshop:

  • Selecting the Longest Chain
  • Consensus Protocol including Proof of Work
  • Public Key Encryption and Digital Signatures
  • Communicating with other nodes; peer-to-peer networking

Where to go to learn more:

Bitcoin Whitepaper

Mastering Bitcoin Book

Coursera - Bitcoin and Cryptocurrency Technology

A blockchain in 200 lines of code

Learn Blockchains By Building One

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