# Bitcoin standards implementation libraries
[](https://codecov.io/gh/BP-WG/bp-std)
[](https://crates.io/crates/bp-std)
[](https://docs.rs/bp-std)
[](./LICENSE)
Modern, minimalistic & standard-compliant wallet-level libraries: an alternative
to `rust-bitcoin` and BDK libraries from [LNP/BP Standards Association][Assoc].
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](#descriptors);
- **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][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 tempaltes][#script-templates] convertable 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][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](CONTRIBUTING.md)
## More information
### MSRV
This library requires minimum rust compiler version (MSRV) 1.60.0.
### 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](LICENSE) file for the license details.
[Assoc]: https://lnp-bp.org
[bp-primitives]: https://crates.io/crates/bp-primitives
[bp-core]: https://github.com/BP-WG/bp-core
[orlovsky]: https://github.com/dr-orlovsky
[descriptor-wallet]: https://github.com/BP-WG/descriptor-wallet