UTXO on Substrate

A UTXO chain implementation on Substrate, with two self-guided workshops. Original UXTO inspiration by Dmitriy Kashitsyn.

Substrate Version: 2.0.0-rc6. For educational purposes only.

Table of Contents

• Installation: Setting up Rust & Substrate dependencies

• UI Demo: Demo of UTXO implementation in a simple UI

• Beginner Workshop: A self guided, 1 hour workshop that familiarizes you with Substrate.

• Advanced Workshop: A self guided, 2 hour video tutorial, that teaches you how to build a UTXO blockchain from scratch.

• Helpful Resources: Additional supporting documentation and references for troubleshooting.

Installation

1. Install or update Rust

curl https://sh.rustup.rs -sSf | sh

# On Windows, download and run rustup-init.exe
# from https://rustup.rs instead

rustup update nightly
rustup target add wasm32-unknown-unknown --toolchain nightly
rustup update stable

2. Clone this workshop

Clone your copy of the workshop codebase

git clone https://github.com/substrate-developer-hub/utxo-workshop.git

UI Demo

In this UI demo, you will interact with the UTXO blockchain via the Polkadot UI.

The following example takes you through a scenario where:

• Alice already owns a UTXO of value 100 upon genesis
• Alice sends Bob a UTXO with value 50, tipping the remainder to validators

1. Compile and build a release node

cargo build --release

2. Start a node. The --dev flag will start a single mining node, and the --tmp flag will start it in a new temporary directory.

./target/release/utxo-workshop --dev --tmp

3. In the console note the helper printouts. In particular, notice the default account Alice already has 100 UTXO within the genesis block.

4. Open Polkadot JS making sure the client is connected to your local node by going to Settings > General and selecting Local Node in the remote node dropdown.

5. Declare custom datatypes in PolkadotJS as the frontend cannot automatically detect this information. To do this, go to Settings > Developer tab and paste in the following JSON:

{
  "Address": "AccountId",
  "LookupSource": "AccountId",
  "Value": "u128",
  "TransactionInput": {
    "outpoint": "Hash",
    "sigscript": "H512"
  },
  "TransactionOutput": {
    "value": "Value",
    "pubkey": "Hash"
  },
  "Transaction": {
    "inputs": "Vec<TransactionInput>",
    "outputs": "Vec<TransactionOutput>"
  },
  "Difficulty": "U256",
  "DifficultyAndTimestamp": {
    "difficulty": "Difficulty",
    "timestamp": "Moment"
  },
  "Public": "H256"
}

6. Confirm that Alice already has 100 UTXO at genesis. In Chain State > Storage, select utxo. Input the hash 0x76584168d10a20084082ed80ec71e2a783abbb8dd6eb9d4893b089228498e9ff. Click the + notation to query blockchain state.

   Notice that:

   • This UTXO has a value of 100
   • This UTXO belongs to Alice's pubkey. You use the subkey tool to confirm that the pubkey indeed belongs to Alice

7. Spend Alice's UTXO, giving 50 to Bob. In the Extrinsics tab, invoke the spend function from the utxo pallet, using Alice as the transaction sender. Use the following input parameters:

   • outpoint: 0x76584168d10a20084082ed80ec71e2a783abbb8dd6eb9d4893b089228498e9ff
   • sigscript: 0x6ceab99702c60b111c12c2867679c5555c00dcd4d6ab40efa01e3a65083bfb6c6f5c1ed3356d7141ec61894153b8ba7fb413bf1e990ed99ff6dee5da1b24fd83
   • value: 50
   • pubkey: 0x8eaf04151687736326c9fea17e25fc5287613693c912909cb226aa4794f26a48

   Send as an unsigned transaction. With UTXO blockchains, the proof is already in the sigscript input.

8. Verify that your transaction succeeded. In Chain State, look up the newly created UTXO hash: 0xdbc75ab8ee9b83dcbcea4695f9c42754d94e92c3c397d63b1bc627c2a2ef94e6 to verify that a new UTXO of 50, belonging to Bob, now exists! Also you can verify that Alice's original UTXO has been spent and no longer exists in UtxoStore.

Coming soon: A video walkthrough of the above demo.

Beginner Workshop

Estimated time: 2 hours

In this workshop you will:

• Get familiar with basic Rust and Substrate functionality
• Prevent malicious users from sending bad UTXO transactions

Your challenge is to fix the code such that:

1. The Rust compiler compiles without any errors
2. All tests in utxo.rs pass, ensuring secure transactions

Directions

1. Checkout the workshop branch. The Master branch has the solutions, so don't peek!

git fetch origin workshop:workshop
git checkout workshop

2. Cd into the base directory. Run the test using: cargo test -p utxo-runtime.

compiling utxo-runtime v2.0.0 (/Users/nicole/Desktop/utxo-workshop/runtime)
error[E0433]: failed to resolve: use of undeclared type or module `H512`
   --> /Users/nicole/Desktop/utxo-workshop/runtime/src/utxo.rs:236:31
    |
236 |             input.sigscript = H512::zero();
    |                               ^^^^ use of undeclared type or module `H512`

...

3. Your first task: fix all the compiler errors! Hint: Look for the TODO comments in utxo.rs to see where to fix errors.

4. Once your code compiles, it's now time to fix the 8 failing tests!

failures:
    utxo::tests::attack_by_double_counting_input
    utxo::tests::attack_by_double_generating_output
    utxo::tests::attack_by_over_spending
    utxo::tests::attack_by_overflowing_value
    utxo::tests::attack_by_permanently_sinking_outputs
    utxo::tests::attack_with_empty_transactions
    utxo::tests::attack_with_invalid_signature
    utxo::tests::test_simple_transaction

5. In utxo.rs, edit the logic in validate_transaction() function to make all tests pass.

running 8 tests
test utxo::tests::attack_by_overflowing_value ... ok
test utxo::tests::attack_by_double_counting_input ... ok
test utxo::tests::attack_by_double_generating_output ... ok
test utxo::tests::attack_by_over_spending ... ok
test utxo::tests::attack_with_empty_transactions ... ok
test utxo::tests::attack_with_invalid_signature ... ok
test utxo::tests::attack_by_permanently_sinking_outputs ... ok
test utxo::tests::test_simple_transaction ... ok

Advanced Workshop

VIDEO TUTORIALS COMING SOON

Estimated time: 2 hours

In this workshop, you will implement this UTXO project from scratch using Substrate.

You will learn:

• How to implement the UTXO ledger model on Substrate
• How to secure UTXO transactions against attacks
• How to seed genesis block with UTXOs
• How to reward block validators in this environment
• How to customize transaction pool logic on Substrate
• Good coding patterns for working with Substrate & Rust, including testing and refactoring

Checkout the startercode branch to get the boilerplate for this workshop.

git fetch origin startercode:startercode
git checkout startercode

Helpful Resources

• Substrate documentation
• bytes to Vec converter
• Polkadot UI