Client-side-validation commit-verify library

This is an implementation of LNPBP-8 single-use-seal abstraction. Specifically, it provides a set of traits that allow to implement Peter's Todd single-use seal paradigm. Information in this file partially contains extracts from Peter's works listed in "Further reading" section.

The library is a part of more generic client_side_validation library covering other client-side-validation standards. Client-side-validation is a paradigm for distributed computing, based on top of proof-of-publication/ commitment medium layer, which may be a bitcoin blockchain or other type of distributed consensus system.

The development of the library is supported by LNP/BP Standards Association and is performed on its GitHub page.

Minimum supported rust version for the library (MSRV) is 1.66 and 2021 rust edition.

Documentation

Detailed developer & API documentation for the library can be accessed at https://docs.rs/single_use_seals/

To learn about the technologies enabled by the library please check slides from our tech presentations and LNP/BP tech talks videos

Usage

To use the library, you just need to reference the latest version, in [dependencies] section of your project Cargo.toml.

single_use_seals = "1"

If you are using other client-side-validation libraries, consider importing just a single client_side_validation library which re-exports all of them, including the current one.

The library does not expose any feature flags and have only a single dependency on amplify_derive crate, also created and supported by the LNP/BP Association.

More information

Single-use-seals definition

Analogous to the real-world, physical, single-use-seals used to secure shipping containers, a single-use-seal primitive is a unique object that can be closed over a message exactly once. In short, a single-use-seal is an abstract mechanism to prevent double-spends.

A single-use-seal implementation supports two fundamental operations:

• Close(l,m) → w — Close seal l over message m, producing a witness w.
• Verify(l,w,m) → bool — Verify that the seal l was closed over message m.

A single-use-seal implementation is secure if it is impossible for an attacker to cause the Verify function to return true for two distinct messages m1, m2, when applied to the same seal (it is acceptable, although non-ideal, for there to exist multiple witnesses for the same seal/message pair).

Practical single-use-seal implementations will also obviously require some way of generating new single-use-seals:

• Gen(p)→l — Generate a new seal basing on some seal definition data p.

Terminology

Single-use-seal: a commitment to commit to some (potentially unknown) message. The first commitment (i.e. single-use-seal) must be a well-defined (i.e. fully specified and unequally identifiable in some space, like in time/place or within a given formal informational system). Closing of a single-use-seal over message: a fulfilment of the first commitment: creation of the actual commitment to some message in a form unequally defined by the seal. Witness: data produced with closing of a single use seal which are required and sufficient for an independent party to verify that the seal was indeed closed over a given message (i.e. the commitment to the message had been created according to the seal definition).

NB: It's important to note, that while its possible to deterministically define was a given seal closed it yet may be not possible to find out if the seal is open; i.e. seal status may be either "closed over message" or "unknown". Some specific implementations of single-use-seals may define procedure to deterministically prove that a given seal is not closed (i.e. opened), however this is not a part of the specification and we should not rely on the existence of such possibility in all cases.

Trait structure

The module defines trait SealProtocol that can be used for implementation of single-use-seals with methods for seal close and verification. A type implementing this trait operates only with messages (which is represented by any type that implements AsRef<[u8]>,i.e. can be represented as a sequence of bytes) and witnesses (which is represented by an associated type SealProtocol::Witness). At the same time, SealProtocol can't define seals by itself.

Seal protocol operates with a *seal medium *: a proof of publication medium on which the seals are defined.

The module provides two options of implementing such medium: synchronous SealProtocol and asynchronous SealProtocolAsync.

Sample implementation

Examples of implementations can be found in bp::seals module of bp-core crate.

Further reading

• Peter Todd. Preventing Consensus Fraud with Commitments and Single-Use-Seals. https://petertodd.org/2016/commitments-and-single-use-seals.
• Peter Todd. Scalable Semi-Trustless Asset Transfer via Single-Use-Seals and Proof-of-Publication. 1. Single-Use-Seal Definition. https://petertodd.org/2017/scalable-single-use-seal-asset-transfer

Contributing

Contribution guidelines can be found in CONTRIBUTING

Licensing

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