Blue Bird

Blockchain Foundations

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These are programming exercises.

The exercises ask you to gradually build a node for the course's blockchain network, Marabu. The full protocol is described in the protocol specification.

Some exercises divert from the main node development and are simple independent programming exercises.

Exercise 0

Due 2021-06-17

Start coding the implementation of your Marabu node. In this exercise, you will set up your repository and exchange a 'hello' message with any peer connecting to you.

  • Decide what programming language you will use. We recommend a language you are proficient in.
  • Find a nice name for your node!
  • Share your repository URL on GitHub/GitLab so that we can put it on the course website.
  • Implement the networking core of your node. Your node must listen to TCP port 18018 (or a port of your choice) for connections.
  • Implement message parsing, defragmentation, and canonical JSON encoding and decoding.
  • Implement the protocol handshake using the hello messages.

Exercise 1

Due 2021-06-17

In this exercise, you will extend your Marabu node so that it can exchange messages and perform peer discovery.

  • Implement peer discovery bootstrapping by hard-coding some peers.
  • Store a list of discovered peers locally. These should survive reboots.
  • Implement peer discovery using the getpeers and peers messages.
  • Devise a policy to decide which peers to connect to and how many to connect to.

Exercise 2

Due 2021-06-22

In this exercise, you will extend your Marabu node to implement content addressable object exchange and gossiping.

  • Maintain a local database of known objects.
  • Implement object exchange using the getobject, ihaveobject, object messages.
  • Reject objects that are already known.
  • Accept objects that are new and store them in your database.
  • Implement gossiping. Broadcast the knowledge of newly received objects to your peers.

Exercise 3

Due 2021-07-02

In this exercise, you will implement transaction generation and validation for your Marabu node.

  • Create the logic to represent a transaction.
  • A transaction has inputs and outputs.
  • Transactions are addressed by txids that are calculated by hashing.
  • Inputs contain outpoints and signatures.
  • Outpoints are txids and indexes.
  • Outpoint validation ensures txid and index existence.
  • Input validation ensures outpoint validity and signature validity.
  • Signature validation requires running the cryptographic signature check.
  • Outputs contain a public key and a value.
  • The public keys must be in the correct format.
  • Transactions must respect the law of conservation.
  • Private keys can sign transaction inputs pointing to their public key.
  • When you receive a transaction object from the network, validate it before gossiping it.

Don't worry about maintaining a perfect UTXO set just yet. We'll focus on this in Exercise 7.

To test your implementation, you may use the following transactions (the first is a coinbase, the second spends from the first):

{"type": "transaction", "outputs": [{"pubkey": "77bd8ef0bf4d9423f3681b01f8b5b4cfdf0ee69fb356a7762589f1b65cdcab63", "value": 50000000000}]}

{"type": "transaction", "inputs": [{"outpoint": {"txid": "5c532068dcbedde528e788eb8a36f44110162685572d5834c81b50af6d27390d", "index": 0}, "sig": "aed4d1f13933e195f68add86915c099366f7d198602afb13551df5575dc57013b83d84f70b310e28c72b0c143d8fab6ce2fc38a7f88d466d1ccc88a4b2970809"}], "outputs": [{"pubkey": "77bd8ef0bf4d9423f3681b01f8b5b4cfdf0ee69fb356a7762589f1b65cdcab63", "value": 10}]}

Exercise 4

Due 2021-07-09

Solve the following blockchain-course.org exercises:

  • "Breaking SHA256"
  • "Performing proof-of-work"

Exercise 5

Due 2021-07-09

In this exercise, you will implement block validation in your Marabu node.

  • Create the logic to represent a block.
  • Check the proof-of-work.
  • Ensure the target is the one required.
  • Check that all contained transactions are valid.
  • Check for coinbase transactions.
  • When you receive a block object from the network, validate it before gossiping it.

Exercise 6

Due 2021-07-09

In this exercise, you will implement chain validation in your Marabu node.

  • Implement the longest chain rule.
  • Ensure the first block in the chain is genesis.
  • Ensure timestamps are increasing.
  • Implement getchaintip/chaintip.
  • Use getchaintip to inquire others about their chains.
  • Download chains recursively from tip to genesis.
  • Handle the coinbase transaction.

Exercise 7

Due 2021-07-16

In this exercise, you will maintain a mempool of transactions in your Marabu node.

  • Listen for transactions as they are gossiped on the network.
  • Keep track of which transactions have been confirmed and which one have not.
  • Maintain a mempool of unconfirmed transactions.
  • Implement mempool/getmempool.
  • Maintain a UTXO.
  • Update your UTXO as blocks and transactions arrive.
  • Modify your chain validation to ensure transactions do not double spent.
  • Update your UTXO when your mempool does not match a newly mined block.
  • Deal with UTXO updates when the chain reorgs.

Exercise 8

Due 2021-07-16

In this exercise, you will implement your own miner for your Marabu node.

  • Collect transactions in your mempool into a block.
  • Create the logic to build a block template.
  • Mine on the candidate block to discover proof-of-work.
  • Benchmark and optimize your miner. What hashrate can you achieve?
  • Broadcast your newly discovered block when it is found.

Exercise 9

Due 2021-07-23

In this exercise, you will try to attack your peers. Look at the source code of the implementations of three of your fellow students.

  • Find at least one attack against each of your peers.
  • Discuss and fix the attacks that your peers found on your node.

You can perform network-level attacks, denial of service attacks, or attack their transaction and block validation.

Exercise 10

Due 2021-07-30

Solve the "Constructing a Merkle Tree" assignment on blockchain-course.org.

Exercise 11

Due 2021-08-06

Solve the following blockchain-course.org exercises:

  • "Say hello to Ethereum"
  • "Simple storage smart contract"
  • "Faucet smart contract"
  • "ERC-20 token"

Exercise 12

Due 2021-08-06

Solve the following blockchain-course.org exercises:

  • "Dutch Auction Implementation"
  • "Name Service"
  • "Vickrey Auction Implementation"
  • "Game of Thrones"

Exercise 13

Due 2021-08-13

Implement SPV verification for your Marabu node. Participate in the hard fork.

Exercise 14

Due 2021-08-20

Difficulty adjustment. Participate in the hard fork.