Crate vsss_rs_std 

Verifiable Secret Sharing Schemes are using to split secrets into multiple shares and distribute them among different entities, with the ability to verify if the shares are correct and belong to a specific set. This crate includes Shamir’s secret sharing scheme which does not support verification but is more of a building block for the other schemes.

This crate supports Feldman and Pedersen verifiable secret sharing schemes.

Feldman and Pedersen are similar in many ways. It’s hard to describe when to use one over the other. Indeed both are used in http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.134.6445&rep=rep1&type=pdf.

Feldman reveals the public value of the verifier whereas Pedersen’s hides it.

Feldman and Pedersen are different from Shamir when splitting the secret. Combining shares back into the original secret is identical across all methods and is available for each scheme for convenience.

This crate is no-standard compliant and uses const generics to specify sizes.

This crate supports 255 as the maximum number of shares to be requested. Anything higher is pretty ridiculous but if such a use case exists please let me know.

Shares are represented as byte arrays. Shares can represent finite fields or groups depending on the use case. The first byte is reserved for the share identifier (x-coordinate) and everything else is the actual value of the share (y-coordinate).

When specifying share sizes, use the field size in bytes + 1 for the identifier.

To split a p256 secret using Shamir

use vsss_rs_std::{*, shamir};
use elliptic_curve::ff::PrimeField;
use p256::{NonZeroScalar, Scalar, SecretKey};

let mut osrng = rand_core::OsRng::default();
let sk = SecretKey::random(&mut osrng);
let nzs = sk.to_nonzero_scalar();
let res = shamir::split_secret::<Scalar, _>(2, 3, *nzs.as_ref(), &mut osrng);
assert!(res.is_ok());
let shares = res.unwrap();
let res = combine_shares::<Scalar>(&shares);
assert!(res.is_ok());
let scalar = res.unwrap();
let nzs_dup =  NonZeroScalar::from_repr(scalar.to_repr()).unwrap();
let sk_dup = SecretKey::from(nzs_dup);
assert_eq!(sk_dup.to_bytes(), sk.to_bytes());

To split a k256 secret using Shamir

use vsss_rs_std::{*, shamir};
use elliptic_curve::ff::PrimeField;
use k256::{NonZeroScalar, Scalar, ProjectivePoint, SecretKey};

let mut osrng = rand_core::OsRng::default();
let sk = SecretKey::random(&mut osrng);
let secret = *sk.to_nonzero_scalar();
let res = shamir::split_secret::<Scalar, _>(2, 3, secret, &mut osrng);
assert!(res.is_ok());
let shares = res.unwrap();
let res = combine_shares::<Scalar>(&shares);
assert!(res.is_ok());
let scalar = res.unwrap();
let nzs_dup = NonZeroScalar::from_repr(scalar.to_repr()).unwrap();
let sk_dup = SecretKey::from(nzs_dup);
assert_eq!(sk_dup.to_bytes(), sk.to_bytes());

Feldman or Pedersen return extra information for verification using their respective verifiers

use vsss_rs_std::{*, feldman};
use bls12_381_plus::{Scalar, G1Projective};
use elliptic_curve::ff::Field;

let mut rng = rand_core::OsRng::default();
let secret = Scalar::random(&mut rng);
let res = feldman::split_secret::<Scalar, G1Projective, _>(2, 3, secret, None, &mut rng);
assert!(res.is_ok());
let (shares, verifier) = res.unwrap();
for s in &shares {
    assert!(verifier.verify(s).is_ok());
}
let res = combine_shares::<Scalar>(&shares);
assert!(res.is_ok());
let secret_1 = res.unwrap();
assert_eq!(secret, secret_1);

Curve25519 is not a prime field but this crate does support it using features=["curve25519"] which is enabled by default. This feature wraps curve25519-dalek libraries so they can be used with Shamir, Feldman, and Pedersen.

Here’s an example of using Ed25519 and x25519

use curve25519_dalek::scalar::Scalar;
use ed25519_dalek::SecretKey;
use vsss_rs_std::{curve25519::WrappedScalar, *};
use x25519_dalek::StaticSecret;

let mut osrng_7 = rand_7::rngs::OsRng::default();
let mut osrng_8 = rand::rngs::OsRng::default();
let sc = Scalar::random(&mut osrng_7);
let sk1 = StaticSecret::from(sc.to_bytes());
let ske1 = SecretKey::from_bytes(&sc.to_bytes()).unwrap();
let res = shamir::split_secret::<WrappedScalar, _>(2, 3, sc.into(), &mut osrng_8);
assert!(res.is_ok());
let shares = res.unwrap();
let res = combine_shares::<WrappedScalar>(&shares);
assert!(res.is_ok());
let scalar = res.unwrap();
assert_eq!(scalar.0, sc);
let sk2 = StaticSecret::from(scalar.0.to_bytes());
let ske2 = SecretKey::from_bytes(&scalar.0.to_bytes()).unwrap();
assert_eq!(sk2.to_bytes(), sk1.to_bytes());
assert_eq!(ske1.to_bytes(), ske2.to_bytes());

Re-exports

pub use pedersen::PedersenResult;

pub use shamir::combine_shares;

pub use shamir::combine_shares_group;

pub use curve25519_dalek;curve25519

pub use elliptic_curve;

pub use sha2_9;curve25519

pub use subtle;

Modules

curve25519curve25519

Curve25519 is not a prime order curve Since this crate relies on the ff::PrimeField and Curve25519 does work with secret sharing schemes This code wraps the Ristretto points and scalars in a facade to be compliant to work with this library. The intent is the consumer will not have to use these directly since the wrappers implement the From and Into traits.

feldman

Feldman’s Verifiable secret sharing scheme. (see https://www.cs.umd.edu/~gasarch/TOPICS/secretsharing/feldmanVSS.pdf.

pedersen

Pedersen’s Verifiable secret sharing scheme. (see https://www.cs.cornell.edu/courses/cs754/2001fa/129.PDF)

shamir

Secret splitting for Shamir Secret Sharing Scheme and combine methods for field and group elements

Structs

FeldmanVerifier

A Feldman verifier is used to provide integrity checking of shamir shares T commitments are made to be used for verification.

PedersenVerifier

A Pedersen verifier is used to provide integrity checking of shamir shares T commitments are made to be used for verification.

Polynomial

The polynomial used for generating the shares

Share

A Shamir simple secret share provides no integrity checking The first byte is the X-coordinate or identifier The remaining bytes are the Y-coordinate

Enums

Error

Errors during secret sharing

Type Aliases

VsssResult

Results returned by this crate