Update description of single-use-seals crate

Author: dr-orlovsky

single_use_seals/README.md

@@ -10,20 +10,18 @@
 [![unsafe forbidden](https://img.shields.io/badge/unsafe-forbidden-success.svg)](https://github.com/rust-secure-code/safety-dance/)
 [![Apache-2 licensed](https://img.shields.io/crates/l/single_use_seals)](./LICENSE)
 
-This is an implementation of [LNPBP-4] multi-commitment standard and [LNPBP-9] 
-standard, defining to cryptographic commitment schemes used in 
-client-side-validation. It is a part of more generic [`client_side_validation`] 
-library covering other client-side-validation standards.
+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.
 
-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 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](https://lnp-bp.org).
-The original idea of client-side-validation was proposed by Peter Todd with its
-possible applications designed by Giacomo Zucco. It was shaped into a protocol-
-level design by Dr Maxim Orlovsky with a big input from the community and
-implemented by him as this set of libraries.
 
 
 ## Documentation
@@ -38,7 +36,7 @@ and [LNP/BP tech talks videos](https://www.youtube.com/channel/UCK_Q3xcQ-H3ERwAr
 
 ## Usage
 
-To use the library, you just need to reference a latest version, in 
+To use the library, you just need to reference the latest version, in 
 `[dependencies]` section of your project `Cargo.toml`.
 
 ```toml
@@ -52,6 +50,81 @@ 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 being 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
 
@@ -64,3 +137,4 @@ The libraries are distributed on the terms of Apache 2.0 opensource license.
 See [LICENCE](LICENSE) file for the license details.
 
 [`client_side_validation`]: https://crates.io/crates/client_side_validation
+[LNPBP-8]: https://github.com/LNP-BP/LNPBPs/blob/master/lnpbp-0008.md