The author is NOT a cryptographer and has not tested the libraries used or the code nor has anyone reviewed the work. This means it's very likely a fatal flaw somewhere. This is meant only as educational and is not production ready.

Ecash implementation based on David Wagner's variant of Chaumian blinding. Token logic based on minicash (description) which implements a Blind Diffie-Hellman Key Exchange scheme written down by Ruben Somsen here. The database mechanics and the Lightning backend uses parts from LNbits.

Big thanks to phyro for their work and further discussions and improvements.

Install

Prerequisites

These steps help you install Python via pyenv and Poetry. If you already have Poetry running on your computer, you can skip this step and jump right to Install Cashu.

sudo apt install -y build-essential pkg-config libffi-dev libpq-dev zlib1g-dev libssl-dev python3-dev
# on mac: brew install postgres

# install python using pyenv
curl https://pyenv.run | bash

echo export PYENV_ROOT=\"$HOME/.pyenv\" >> ~/.bashrc
echo command -v pyenv >/dev/null || export PATH=\"$PYENV_ROOT/bin:$PATH\" >> ~/.bashrc
source ~/.bashrc
echo eval \"$(pyenv init -)\" >> ~/.bashrc
echo eval \"$(pyenv virtualenv-init -)\" >> ~/.bashrc
source ~/.bashrc
pyenv install 3.9.13

# install poetry
curl -sSL https://install.python-poetry.org | python3 -
echo export PATH=\"$HOME/.local/bin:$PATH\" >> ~/.bashrc
source ~/.bashrc

Install Cashu

# install cashu
git clone https://github.com/callebtc/cashu.git
cd cashu
pyenv local 3.9.13
poetry install

Configuration

mv .env.example .env
# edit .env file
vim .env

To use the wallet with the public test mint, you need to change the appropriate entries in the .env file.

Test instance

Warning: this instance is just for demonstration only. Currently, only Lightning deposits work but not withdrawals. The server could vanish at any moment so consider any Satoshis you deposit a donation. I will add Lightning withdrawals soon so unless someone comes up with a huge inflation bug, you might be able to claim them back at a later point in time.

Change the appropriate .env file settings to

MINT_HOST=8333.space
MINT_PORT=3338

Using Cashu

Cashu should be now installed. To execute the following commands, activate your virtual Poetry environment via

poetry shell

If you don't activate your environment, just prepent poetry run to all following commands.

Using the wallet

Request a mint

This command will return a Lightning invoice and a payment hash. You have to pay the invoice before you can receive the tokens. Note: Minting tokens involves two steps: requesting a mint, and actually minting tokens (see below).

cashu mint 420

Returns:

Balance: 0 sat (Available: 0 sat in 0 tokens)
{
    'pr': 'lnbc4200n1p3jp5clsp5vcfkyqtnkcx9287auhesqwj40che77pd4ymaltc3ruazh3vcgs3qpp5qzwkavpd4pmfkdmq9trdnrk2lswkt0fypqg55h2sucx6yq9ushzsdq4vdshx6r4ypjx2ur0wd5hgxqyjw5qcqpjrzjq0qly7quwdwq2wr52et5gl65dagdgqdwgn9an58mhejnsvmmu996xzetgvqqwzcqqqqqqqqqqqqqqqqq9q9qyysgqfjwnl4za4naf7l2wwcck2gk6y9mvjt5dz9gptfkpl0j50ygkdkuxyjcy3zgd2tk4995yw8gx39cx2qwm9dgwc0t9t6hrgvjzauykqrqpgw0xx3', 
    'hash': '009d6eb02da8769b37602ac6d98ecafc1d65bd2408114a5d50e60da200bc85c5'
}

Mint tokens

After paying the invoice, copy the hash value from above and add it to the command

cashu mint 420 --hash=009d6eb02da8769b37602ac6d98ecafc1d65bd2408114a5d50e60da200bc85c5

You should see your balance update accordingly:

Balance: 0 sat (Available: 0 sat in 0 tokens)
Balance: 420 sat (Available: 420 sat in 4 tokens)

Available tokens here means those tokens that have not been reserved for sending.

Check balance

cashu balance

Send tokens

To send tokens to another user, enter

cashu send 69

You should see the encoded token. Copy the token and send it to another user such as via email or a messenger. The token looks like this:

W3siYW1vdW50IjogMSwgIkMiOiB7IngiOiAzMzg0Mzg0NDYzNzAwMTY1NDA2MTQxMDY3Mzg1MDg5MjA2MTU2NjQxMjM4Nzg5MDE4NzAzODg0NjAwNDUzNTAwNzY3...

You can now see that your available balance has dropped by the amount that you reserved for sending if you enter cashu balance:

Balance: 420 sat (Available: 351 sat in 7 tokens)

Receive tokens

To receive tokens, another user enters:

cashu receive W3siYW1vdW50IjogMSwgIkMiOi...

You should see the balance increase:

Balance: 0 sat (Available: 0 sat in 0 tokens)
Balance: 69 sat (Available: 69 sat in 3 tokens)

Burn tokens

The sending user needs to burn (invalidate) their tokens from above, otherwise they will try to double spend them (which won't work because the server keeps a list of all spent tokens):

cashu burn W3siYW1vdW50IjogMSwgIkMiOi...

Returns:

Balance: 420 sat (Available: 351 sat in 7 tokens)
Balance: 351 sat (Available: 351 sat in 7 tokens)

Run a mint yourself

This command runs the mint on your local computer. Skip this step if you want to use the public test mint instead.

mint

You can turn off Lightning support and mint as many tokens as you like by setting LIGHTNING=FALSE in the .env file.