Overview

C++ Bitcoin library for 32-bit microcontrollers. The library supports Arduino IDE, ARM mbed and bare metal.
It provides a collection of convenient classes for Bitcoin: private and public keys, HD wallets, generation of the recovery phrases, PSBT transaction format, scripts — everything required for a hardware wallet or other bitcoin-powered device.

The library should work on any decent 32-bit microcontroller, like esp32, riscV, stm32 series and others. It doesn't work on 8-bit microcontrollers like a classic Arduino as these microcontrollers are not powerful enough to run complicated crypto algorithms.

We use elliptic curve implementation from trezor-crypto. API is inspired by Jimmy Song's Porgramming Blockchain class and the book.

Documentation

Check out our tutorial where we write a minimal hardware wallet, or browse the API docs. We also have a collection of recepies for some common use-cases.

Alternative libraries

DIY Bitcoin Hardware website has a nice collection of bitcoin-related projects, resources and libraries for makers.

A few bitcoin libraries:

• secp256k1 — elliptic curve library from Bitcoin Core and a version working with Arduino IDE & Mbed out of the box.
• libwally - bitcoin library from Blockstream and a version working with Arduino IDE.
• f469-disco - micropython bitcoin bundle for STM Discovery board and other platforms.

Installation

Search for uBitcoin in Arduino Library Manager and install it.

Alternatively, download the zip file from our repository and select in Arduino IDE Sketch → Include library → Add .ZIP library....

Or clone it directly into your Documents/Arduino/libraries folder:

git clone https://github.com/micro-bitcoin/uBitcoin.git

When installed you will also see a few examples in File → Examples → Bitcoin menu.

Basic usage example

First, don't forget to include necessary headers:

// we use these two in our sketch:
#include "Bitcoin.h"
#include "PSBT.h"       // if using PSBT functionality
// other headers of the library
#include "Conversion.h" // to get access to functions like toHex() or fromBase64()
#include "Hash.h"       // if using hashes in your code

Now we can write a simple example that does the following:

1. Creates a master private key from a recovery phrase and empty password
2. Derives account and prints master public key for a watch-only wallet (zpub in this case)
3. Derives and print first segwit address
4. Parses, signs and prints signed PSBT transaction

// derive master private key
HDPrivateKey hd("add good charge eagle walk culture book inherit fan nature seek repair", "");
// derive native segwit account (bip-84) for tesnet
HDPrivateKey account = hd.derive("m/84'/1'/0'/");
// print xpub: vpub5YkPqVJTA7gjK...AH2rXvcAe3p781G
Serial.println(account.xpub());
// or change the account type to UNKNOWN_TYPE to get tpub
HDPublicKey xpub = account.xpub();
xpub.type = UNKNOWN_TYPE;
// this time prints tpubDCnYy4Ty...dL4fLKsBFjFQwz
Serial.println(xpub);
// set back correct type to get segwit addresses by default
xpub.type = P2WPKH;
Serial.println(hd.fingerprint());

// print first address: tb1q6c8m3whsag5zadgl32nmhuf9q0qmtklws25n6g
Serial.println(xpub.derive("m/0/0").address());

PSBT tx;
// parse unsigned transaction
tx.parseBase64("cHNidP8BAHECAAAAAUQS8FqBzYocPDpeQmXBRBH7NwZHVJF39dYJDCXxq"
"zf6AAAAAAD+////AqCGAQAAAAAAFgAUuP0WcSBmiAZYi91nX90hg/cZJ1U8AgMAAAAAABYAF"
"C1RhUR+m/nFyQkPSlP0xmZVxlOqAAAAAAABAR/gkwQAAAAAABYAFNYPuLrw6igutR+Kp7vxJ"
"QPBtdvuIgYDzkBZaAkSIz0P0BexiPYfzInxu9mMeuaOQa1fGEUXcWIYoyAeuFQAAIABAACAA"
"AAAgAAAAAAAAAAAAAAiAgMxjOiFQofq7l9q42nsLA3Ta4zKpEs5eCnAvMnQaVeqsBijIB64V"
"AAAgAEAAIAAAACAAQAAAAAAAAAA");
// sign with the root key
tx.sign(hd);
// print signed transaction
Serial.println(tx.toBase64());

Ready for more? Check out the tutorial and start writing your very own hardware wallet!