cashu 0.4.2

Ecash wallet and mint with Bitcoin Lightning support

cashu

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.

Cashu client protocol · Quick Install · Manual install · Configuration · Using Cashu · Run a mint

Cashu client protocol

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.

Easy Install

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. On macOS, you might have to run pip install wheel and brew install pkg-config.

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

Hard install: Poetry

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.

Poetry: Prerequisites

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

Poetry: Install Cashu

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

Poetry: Update Cashu

To update Cashu to the newest version enter

git pull && poetry install

Poetry: 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 prepend poetry run to all following commands.

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 info

Returns:

Version: 0.4.2
Debug: False
Cashu dir: /home/user/.cashu
Wallet: wallet
Mint URL: https://8333.space:3338

Get Cashu info

cashu balance

Check balance

cashu balance

Generate a Lightning invoice

This command will return a Lightning invoice that you need to pay to mint new ecash tokens.

cashu invoice 420

Returns:

Pay this invoice to mint 420 sat:
Invoice: lnbc4200n1p3nfk7zsp522g8wlsx9cvmhtyuyuae48nvreew9x9f8kkqhd2v2umrdtwl2ysspp5w2w6jvcnz4ftcwsxtad5kv3yev62pcp5cvq42dqqrmwtr2k6mk8qdq4vdshx6r4ypjx2ur0wd5hgxqyjw5qcqpjrzjqfe5jlwxmwt4sa4s8mqjqp8qtreqant6mqwwkts46dtawvncjwvhczurxgqqvvgqqqqqqqqnqqqqqzgqyg9qyysgqzaus4lsfs3zzk4ehdzrkxzv8ryu2yxppxyjrune3nks2dgrnua6nv7lsztmyjaf96xp569tf7rxdmfud5q45zmr4xue5hjple6xhcrcpfmveag

Execute this command if you abort the check:
cashu invoice 420 --hash 729da933131552bc3a065f5b4b3224cb34a0e034c3015534001edcb1aadadd8e

Checking invoice ...

The client will check every few seconds if the invoice has been paid. If you abort this step but still pay the invoice, you can use the command cashu invoice <amount> --hash <hash> as described above.

Pay a Lightning invoice

cashu pay lnbc120n1p3jfmdapp5r9jz...

Returns:

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

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)

Use cashu burn -a to burn all used tokens or cashu burn -f to force a spent recheck on all tokens and burn them is they are used. This command is safe to use, it won't burn unspent tokens.

Check pending tokens

cashu pending

Returns

Amount: 64 sat Sent: 2022-09-28 06:53:03 ID: 33025ade-3efa-11ed-9096-16a10f0dbf61

W3siYW1vdW50Ijog...

Amount: 64 sat Sent: 2022-09-28 06:57:25 ID: cf588354-3efa-11ed-b5ec-16a10f0dbf61

W3siYW1vdW50Ijog...

Amount: 128 sat Sent: 2022-09-28 09:57:43 ID: fef371fa-3f13-11ed-b31a-16a10f0dbf61

W3siYW1vdW50Ij...

Balance: 1234 sat (Available: 1234 sat in 7 tokens)

You can either burn these tokens manually when the receiver has redeemed them, or you can receive them yourself if you want to cancel a pending payment.

Running a mint

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

python -m cashu.mint

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