Bitcoin standards implementation libraries

Modern, minimalistic & standard-compliant wallet-level libraries: an alternative to rust-bitcoin and BDK libraries from LNP/BP Standards Association.

The main goals of the libraries are:

fast stabilization of APIs: the library will be targeting v1.0 version within the first year of its development; which should enable downstream crates using the library also to stabilize and not spend too much effort on changing the integration each time the new version of bp-wallet is released;
no use of private keys: the library analyzes wallet state using descriptors and allows to produce unsigned PSBTs, as well as publish and analyze (partially) signed PSBTs - but doesn't provide a signer or a way to work with any private key material (seeds, mnemonics, xprivs, private keys); PSBT files must be signed with some external signers or hardware wallets;
standard-compliance: the library tries to provide full compliance with existing bitcoin standards defined in BIPs and do not use any legacy approaches or "blockchain-not-bitcoin" practices (like the ones provided by BLIPs);
separation of bitcoin consensus and standards: the consensus-related code is not a part of this library; all data structures and business logic which may have consensus meaning and is required for a wallet is separated into an independent [bp-primitives] library (a part of [bp-core] library), which is planned to be more extensively audited and ossified alongside bitcoin protocol (while this library will continue to evolve with better APIs and to match new wallet standards);
extensive use of descriptors: library focuses on defining all parts of a wallet using descriptors; additionally to script pubkey descriptors it also supports xpub descriptors, derivation descriptors, applied to script pubkey descriptor as a whole, and input descriptors for RBFs. You can read more on specific descriptor types in the section below;
script templates: the library allows to provide an arbitrary script as a part of a descriptor, which allows support for BOLT lightning channel transaction and makes it possible to ensure stability in the long run; you can read more about script templates vs miniscript below;
opinionated high-level wallet abstractions: the library provide a set of high-level wallet data structures abstracting away blockchain-level details; helping in writing less boilerplate business logic;
APIs usable in all rust projects and in FFI: the library doesn't use async rust, complex callbacks, threads etc., which allows to keep the API simple, usable from any rust app (like ones using reactive patterns instead of async); at the same time all the data structures of the library are Send + Sync, meaning that they can be used in any multi-thread or async environment;
abstracted blockchain data providers: the library abstracts blockchain indexer APIs (Electrum, Esplora, Bitcoin Core etc.) and also provides their implementation using this library structures.

FAQs

Why not use `rust-bitcoin`?

The library doesn't rely on rust-bitcoin crate. The reasons for that are:

to keep the functionality set small and wallet-specific: rust-bitcoin provides "all in one" solution, covering many parts of bitcoin ecosystem, like bitcoin peer-to-peer protocol, not really used by a wallet;
to keep API stable: rust-bitcoin with each release significantly breaks APIs, being in constant refactoring since early 2022 - a process likely to last for few years more; update of wallet libraries after each major change is painful and takes a lot of developers time and effort, as well as introduces API breaking changes downstream preventing all dependent libraries from stabilization;
separation of private key material: in Rust it is impossible to achieve constant-time production of secret key material, as well as prevent the compiler from copying it all over the machine memory (zeroise and other approaches doesn't prevent that). Thus, providing secret keys alongside other APIs may lead to non-secure design of the wallet and should be avoided;
separation of consensus code from standards: rust-bitcoin provides next to each other consensus-related structures and higher level wallet abstractions, which contradicts to the design decision we are making in this library;
to introduce strong semantic typing: for instance, rust-bitcoin doesn't differentiate different forms of scripts (pubkey, sig, witness etc.), while in this library we are using semantic type approach, providing type-safe variants for each semantically-distinct entity even if it shares the same representation with others.

As one may see from the list, rust-bitcoin design and maintenance approach contradicts to the major aims of this project - in fact, this project was created by Maxim Orlovsky (who was the most active contributor to rust-bitcoin since Q1 2019 till Q2 2022) in order to address these issues using different set of trade-offs, providing an alternative to rust-bitcoin to those who needs it.

Why not use miniscript?

Miniscript is great for many purposes, but it can't be used for many cases, including representation of BOLT-3 lightning channel transaction outputs, re-use of public key in different branches of pre-taproot scripts [1][ms-1]. Miniscript is also still unstable, having recent changes to the semantic due to discovered bugs [2][ms-2] [3][ms-3]; meaning that the descriptors created with miniscript before may not be able to deterministically reproduce the structure of some wallet UTXOs in a future. Finally, the existing Rust miniscript implementation [rust-miniscript] inherits all rust-bitcoin tradeoffs, and is much more unstable in terms of APIs and semantic. Thus, it was decided to use this library to provide an alternative to miniscript with introduction of [script templates][#script-templates] convertible to and from miniscript representation - but with some externally-provided tools instead of adding miniscript as a direct dependency here.

Why not BDK?

BDK is great, but it relies on rust-bitcoin and rust-miniscript and can't be used outside of that ecosystem, inheriting all tradeoffs described above. Since we try to address those trade-offs, we had to create a BDK alternative.

How this project is related to `descriptor-wallet`?

Descriptor wallet was an earlier project by the same authors trying to address rust-bitcoin issues by building on top of it. With the recent v0.30 rust-bitcoin release it became clear that the effort of adoption to API-breaking changes is much higher than creating a new independent project from scratch, while at the same time the new project may address rust-bitcoin issues in much more efficient and elegant way. Thus, it was decided to discontinue descriptor-wallet and start the new bp-wallet project instead.

Design

Script templates

Descriptors

Contributing

Contribution guidelines can be found in CONTRIBUTING

More information

MSRV

Minimum supported rust compiler version (MSRV) is shown in rust-version of Cargo.toml.

Policy on altcoins

Altcoins and "blockchains" other than Bitcoin blockchain/Bitcoin protocols are not supported and not planned to be supported; pull requests targeting them will be declined.

Licensing

The libraries are distributed on the terms of Apache 2.0 opensource license. See LICENCE file for the license details.

BP-WG/bp-std