Cashu is a Chaumian Ecash wallet and mint with Bitcoin Lightning support.

Disclaimer: The author is NOT a cryptographer and this work has not been reviewed. This means that there is very likely a fatal flaw somewhere. Cashu is still experimental and not production-ready.

Cashu is an 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.

There are ongoing efforts to implement alternative Cashu clients that use the same protocol such as a Cashu Javascript wallet. If you are interested in helping with Cashu development, please see the docs for the notation and conventions used.

The easiest way to use Cashu is to install the package it via pip:

pip install cashu

To update Cashu, use pip install cashu -U. If you have problems running the command above on Ubuntu, run sudo apt install -y pip pkg-config libpq-dev. On macOS, run brew install postgresql.

You can skip the entire next section about Poetry and jump right to Using Cashu.

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

# !! follow the instructions of pyenv init to setup pyenv !!
pyenv init

# restart your shell (or source your .rc file), then install python:
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
git clone https://github.com/callebtc/cashu.git
cd cashu
pyenv local 3.9.13
poetry install

To update Cashu to the newest version enter

git pull && poetry install

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 prepend poetry run to all following commands.

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.

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

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'
}

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.

cashu balance

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)

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)

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)

cashu pay lnbc120n1p3jfmdapp5r9jz...

Returns:

Balance: 351 sat (Available: 351 sat in 7 tokens)
Balance: 339 sat (Available: 339 sat in 8 tokens)

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.