# [IntegrityChain]: FIPS 205 Stateless Hash-Based Digital Signature Standard

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[FIPS 205] Stateless Hash-Based Digital Signature Standard written in pure Rust for server, 
desktop, browser and embedded applications. The source repository includes examples demonstrating 
benchmarking, constant-time statistical measurements, and WASM execution.

This crate implements the FIPS 205 **final/released** standard in pure Rust with minimal and mainstream dependencies,
and without any unsafe code. All twelve (!!) security parameter sets are fully functional. The implementation's
key- and signature-generation functionality operates in constant-time, does not require the standard library, e.g. 
`#[no_std]`, has no heap allocations, e.g. no `alloc` needed, and exposes the `RNG` so it is suitable for the full 
range of applications from server down to the bare-metal. The API is stabilized and the code is heavily biased 
towards safety and correctness; further performance optimizations will be implemented as the standard matures.
This crate will quickly follow any changes to FIPS 204 standard/vectors as they become available.

See <https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.205.pdf> for a full description of the target functionality.

The functionality is extremely simple to use, as demonstrated by the following example.

~~~rust
use fips205::slh_dsa_shake_128s; // Could use any of the twelve security parameter sets. 
use fips205::traits::{SerDes, Signer, Verifier};
# use std::error::Error;
#
# fn main() -> Result<(), Box<dyn Error>> {

let msg_bytes = [0u8, 1, 2, 3, 4, 5, 6, 7];

  
// Generate both public and secret keys. This only fails when the OS rng fails.
let (pk1, sk) = slh_dsa_shake_128s::try_keygen()?; 
// Use the secret key to generate a signature. The second parameter is the
// context string (often just an empty &[]), and the last parameter selects
// the preferred hedged variant. This only fails when the OS rng fails.
let sig_bytes = sk.try_sign(&msg_bytes, b"context", true)?;  

  
// Serialize the public key, and send with message and signature bytes. These
// statements model sending byte arrays over the wire.
let (pk_send, msg_send, sig_send) = (pk1.into_bytes(), msg_bytes, sig_bytes);
let (pk_recv, msg_recv, sig_recv) = (pk_send, msg_send, sig_send);

  
// Deserialize the public key. This only fails on a malformed key.
let pk2 = slh_dsa_shake_128s::PublicKey::try_from_bytes(&pk_recv)?;
// Use the public key to verify the msg signature
let v = pk2.verify(&msg_recv, &sig_recv, b"context");
assert!(v); 
# Ok(())
# }
~~~

The detailed Rust [Documentation][docs-link] lives under each **Module** corresponding to the 
desired [security parameter](#modules) below. 

## Notes

* This crate is fully functional and corresponds to the final/released FIPS 205 (August 13, 2024), 
  including the pre-hash variants which formalize methods for signing a hash of the message instead 
  of the message itself (along with metadata about the hasher used).
* Constant-time assurances target the source-code level only, with confirmation via
  manual review/inspection, the embedded target, and the `dudect` dynamic tests.
* Note that FIPS 205 places specific requirements on randomness per section 3.1, hence the exposed `RNG`.
* Requires Rust **1.70** or higher. The minimum supported Rust version may be changed in the future, 
  but it will be done with a minor version bump (when the major version is larger than 0).
* All on-by-default features of this library are covered by `SemVer`.
* The FIPS 205 standard and this software should be considered experimental -- USE AT YOUR OWN RISK!

## License

Contents are licensed under either the [Apache License, Version 2.0](http://www.apache.org/licenses/LICENSE-2.0)
or [MIT license](http://opensource.org/licenses/MIT) at your option.

### Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as 
defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

[//]: # (badges)

[crate-image]: https://img.shields.io/crates/v/fips205
[crate-link]: https://crates.io/crates/fips205
[docs-image]: https://docs.rs/fips205/badge.svg
[docs-link]: https://docs.rs/fips205/
[build-image]: https://github.com/integritychain/fips205/workflows/test/badge.svg
[build-link]: https://github.com/integritychain/fips205/actions?query=workflow%3Atest
[license-image]: https://img.shields.io/badge/license-Apache2.0/MIT-blue.svg
[rustc-image]: https://img.shields.io/badge/rustc-1.70+-blue.svg

[//]: # (general links)

[IntegrityChain]: https://github.com/integritychain/
[FIPS 205]: https://csrc.nist.gov/pubs/fips/205/final