Introduction

This demo has 2 components: create_unsigned_tx.py and sign_tx.py. The former is used for creating transactions, and requires having a master public key (to create addresses), and a full node that is connected and synced to the blockchain. The latter is used for signing transactions, and requires a spend bundle JSON, and a master private key mnemonic (24 words), but it requires no servers, ports, or internet connection.

How to use the demo

These steps are for unhardened keys. For hardened keys it's slightly different.

1. Get two machines, an online and offline machine, and run a node on the online one (testnet or mainnet).
2. Install python 3, create a venv python3 -m venv ./venv in the directory where this README is.
3. Do source ./venv/bin/activate to activate the venv.
4. Do a pip install -r requirements.txt for this project.
5. Create a private key using chia keys generate or chia keys generate_and_print, on an offline machine.
6. Put the 24 words into sign_tx.py file.
7. Run the sign_tx script to get the parent public key and paste it create_unsigned_tx.py, on the online machine.
8. Use the generate_address function in create_unsigned_transaction.py to create new addresses for a specific index, and send some chia (or testnet chia) to these addresses. Note that for testnet, you should use the txch prefix instead of xch when calling this function.
9. Run the create_unsigned_tx.py script and save the JSON spend bundle, on the online machine.
10. Run the sign_tx.py script on the offline machine with your 24 words, and your transaction
11. Copy the signed tx and send it to the full node on the online machine, using the push_tx RPC call.

Hardened vs Unhardened Keys

This demo uses bip32 public key derivation, with the option to use hardened or unhardened keys. With unhardened keys, new public keys / addresses can be created using a master public key, which can be on an online machine. Even if the master pk is revealed, the secret key (sk or private key), is not revealed. Note however, that if one of the child private keys is revealed, all of the other child private keys are also revealed. Please see https://github.com/Chia-Network/chia-blockchain/wiki/Chia-Keys-Architecture for information about keys.

Child public keys derived in this form (called unhardened keys) are NOT part of the EIP-2333 spec, since they are not secure against a quantum attack. If you want more security against quantum attacks, we recommend not using this feature, and instead generating many public keys from your offline machine, and exporting all of them into an online machine. Furthermore, hardened keys do not have the security issue where revealing a child key and the public parent reveals all of the other childs.

If you would like to use hardened private keys, which don't allow deriving new public keys from a master public key, you can also do this. In the sign_tx.py file, there is method which can create many public keys and export them to a file. You can import this file using the create_unsigned_tx.py script. Please read both files to understand how they work.

Transactions

Chia has no concept of transactions in the blockchain. There are spend bundles which can represent an individual transaction, but when a block is created, all spend bundles are combined into one, and all the signatures are aggregated into one. Each block in chia only has one signature. Therefore, each block does not have a list of transactions, but rather a list of added coins and a list of removed coins. You cannot query for transactions on the blockchain, you can only get coins. Use the get_coin_records_for_puzzle_hash to see all spent or unspent coins for a specific puzzle hash. You can find more information about the RPCs here: https://github.com/Chia-Network/chia-blockchain/wiki/RPCExamples.

Changelog

1.3

• Added announcements to ensure the transaction cannot be unbundled
• Added the RESERVE_FEE condition to ensure no stealing of fees
• Show the conditions created by the transaction

1.2

• Change format of unhardened keys, note, the master PK is no longer used. (hardened is used for the top 3 levels)
• Add setup.py so you can do pip install -r requirements.txt, and update instructions.
• Fix a bug with spending multiple coins (the outputs were being duplicated for each input)
• Add checking of cost, so that tx fits in the blockchain

1.1

• Adds support for hardened keys.

1.0

• Initial commit with unhardened keys support.