#1 Open-Sourcing the Design Guide

Update: This bounty has been claimed, view the winning submission here. Special thanks to all the other open-source contributors and submissions. If you would like your submission to be highlighted please email us.

• Benhami1ton’s Submission

2 BTC to port the Bitcoin UI Kit from Figma to an open-source Penpot project. The Bitcoin UI Kit serves as a comprehensive set of design components for individuals involved in developing Bitcoin applications.

Currently, the Bitcoin UI Kit is only available in a Figma file format. This is a limitation because it requires the use of proprietary software. To address this issue and increase accessibility, HRF is sponsoring the replication of the Bitcoin UI Kit on Penpot, recognized as the leading open-source alternative to Figma. Penpot is not only free to use, but also allows the setup of self-hosted instances.

#2 Serverless Payjoin

1 BTC to deploy a production-ready version 2 payjoin protocol which may send and receive Payjoin transactions without requiring a sender or recipient to operate a public server. The solution should not rely on a trusted third party which could expose user privacy in a non-trivial way. The protocol should be asynchronous and use modern, ideally multiplexed, web standards, without heavy dependencies like Tor, in order to promote widespread adoption. Payjoin requests should make use of BIP-21 unified bitcoin URIs. Some degree of backwards-compatibility and ease of integration with existing BIP-78 payjoin will be taken into consideration as elements of a successful solution.

A protocol specification must be published alongside working software as part of the submission for this bounty.

#3 End-to-End Encrypted Nostr Group Chats

Update: 1 BTC of this bounty has been claimed by Martti Malmi for his work incorporating this functionality into Iris. The remaining 1 BTC is open to any popular nostr client that can create end-to-end encrypted nostr group chats with an interoperable standard via a merged NIP.

2 BTC for the creation of end to end encrypted group chats powered by any popular Nostr client that does not leak metadata to third parties. Users must be able to chat with at least two other Nostr users. Outside observers must not be able to see the content of messages, the sender/recipient of messages, or the total number of messages between recipients.

#4 Silent payments

1 BTC for a mobile wallet which can send and receive Silent Payments in a private manner without requiring the user to run a full node. This will require a backend which:

• Can vend the relevant tweak data to the client
• Provide the client with a method for determining if a scriptPubKey exists in a block
• Provide the client with the necessary data to spend the found UTXO (outpoint and amount)

The mobile wallet should be:

• Be open-source
• Multi-platform (Android, iOS)
• Be a backend that can be used by multiple mobile wallets
• Leverage existing protocols as much as possible (Electrum, BIP157/158, etc)
• Minimize bandwidth for the client where possible
  • Opportunistic notifications (as described in the BIP) as way for clients to limit their scanning to once a week / once a month
  • New BIP158 style filter types for only taproot outputs
• Minimize what the server is able to learn about a clients transactions:
  • The server should not know when the client is the owner of a particular UTXO
  • The server should not know when the client is the owner of an output in a particular transaction
• Be compliant with the final BIP

#5 Human Readable Offers

1 BTC for a human-readable bolt 12 offer generator feature integrated into an iOS or android bitcoin wallet. “Human-readable” means something that can be used on feature phone without QR or copy/paste ability. For example, something that looks like LN address. In order for a wallet to qualify they must meet our internal threshold for monthly active users and other indications of a large user base. 

#6 Self-custodial Mobile Lightning address

Update: This bounty has been awarded to Evan Kaloudis for Zeus Wallet. (Special thanks to Supertestnet’s ZapLocker which inspired Zeus Wallet). HRF is aware of debates regarding impacts on the lightning network by this awarded solution. HRF is committed to addressing those concerns with bounties for BOLT 12 and async payments in the future”

1 BTC for an easy-to-setup self-custodial mobile Lightning address generator integrated into an iOS or android bitcoin wallet. The mobile Lightning address should not require the user to set up their own web server. In order for a wallet to qualify they must meet our internal threshold for monthly active users and other indications of a large user base. 

#7 Mobile Border Wallets

Update: This bounty has been awarded to Bitcoin Tribe for their border wallet functionality and for their React Native library to easily implement border wallet functionality into other Bitcoin wallets. 

2 BTC for the integration of border wallet optionality in addition to a seed phrase for a popular iOS or android wallet. The user of the wallet should be easily able to choose to use border wallet functionality to create and memorize their seed. The wallet must allow the user to periodically test their memorized seed to ensure accuracy of memory. The seed words must be BIP-39 compliant, and support either 12 or 24 word seed phrases.

#8 Easy Mobile Multisig

1 BTC for the implementation of a “tap or airdrop to create 2 of 3” multisig functionality between three phones for an open-source iOS or android wallet. The wallet must be self-custodial, with a method for users to recover funds using open-source software outside of the application used to create the multisig. In order for a wallet to qualify they must meet our internal threshold for monthly active users and other indications of a large user base. 

#9 Frost Multisig Wallet

1 BTC to a FROST-powered dynamic mobile multisig that allows you to modify the signer set without moving funds to a new address. The wallet must be self-custodial.

#10 Cashu

A) 0.5 BTC for a fully functional iOS Cashu app

Update: This bounty has been awarded to eNuts Wallet.

B) 0.5 BTC for a fully functional Android Cashu app

Update: This bounty has been awarded to Misovan for Minibits wallet.

In both iOS and Android cases the wallet must be open source, fully function, and support:

• Multiple mints 
• The ability to directly send ecash to Nostr peers from contacts
• The ability to receive ecash over Nostr
• Seed phrase backups to recover lost funds

C) 0.5 BTC for an open source Cashu web widget for anonymous paywalled content.

Update: This bounty has been awarded to Gandlaf for Proxnut

This bounty is for developing a JavaScript frontend widget and a NodeJS backend library that can be deployed as a simple drop-in for any existing website to enable ecash payments. This could be used to build web paywalls or upvoting systems that use ecash instead of a ledger that keeps track of every user’s activity. The website provider should be able to choose one or multiple mints to support. User interactions with the web site can then trigger payments to the website host using the users’s ecash balance. Users should be able to top up and withdraw a Bitcoin balance. The widget should be a web component that can be easily included in a website and possible also a browser extension that can serve multiple websites at once.

D) 0.5 BTC for Cashu-TS backup restore.

Update: This bounty has been awarded to Gandlaf for adding Cashu-TS restore

Cashu-TS is a widely-used Cashu wallet library that provides tremendous value to the ecosystem by serving as a basis for developing mobile wallets or web apps. In order for these application to provide a basic level of security for their users, Cashu-TS needs to support a seed phrase backup scheme which allows for a user experience similar to backing up a Bitcoin wallet. The seed phrase backup and the secret derivation scheme should use BIP32 and BIP39 and adhere to the same protocol rules as the reference implementation Cashu Nutshell so that users can restore their balance across different implementations. By enabling backups in Cashu-TS, every wallet and app using it should be able to benefit from it.

#11 BIP47 Expansion

0.5 BTC each to the first two (2) open-source self-custodial iOS or Android wallets that add send and receive support for BIP47 payment codes. If a wallet already has this functionality as of July 28, 2023, it is not eligible for this bounty. The purpose of this bounty is to encourage new wallets to add BIP47 support in order to expand the number of privacy options available to Bitcoin users. If a wallet has only send *or* receive functionality as of July 28, 2023, that team can claim a 0.5 BTC credit for adding the other half of the functionality. In order for a wallet to qualify they must meet our internal threshold for monthly active users and other indications of a large user base.