Not allowing zero as an x-coordinate in lagrange basis evaluation, adding a check for total > 1, and some docs.

Signed-off-by: lovesh <lovesh.bond@gmail.com>

Author: lovesh

secret_sharing_and_dkg/src/feldman_dvss_dkg.rs

@@ -169,7 +169,7 @@ impl<G: AffineRepr> SharesAccumulator<G> {
 }
 
 /// Reconstruct threshold key using the individual public keys. Multiplies each public key with its
-/// Lagrange coefficient and adds the result
+/// Lagrange coefficient and adds the result. Assumes that public key ids are unique
 pub fn reconstruct_threshold_public_key<G: AffineRepr>(
     public_keys: Vec<(ShareId, G)>,
     threshold: ShareId,

secret_sharing_and_dkg/src/shamir_ss.rs

@@ -35,6 +35,9 @@ pub fn deal_secret<R: RngCore, F: PrimeField>(
     if threshold > total {
         return Err(SSError::InvalidThresholdOrTotal(threshold, total));
     }
+    if total < 2 {
+        return Err(SSError::InvalidThresholdOrTotal(threshold, total));
+    }
     if threshold < 1 {
         return Err(SSError::InvalidThresholdOrTotal(threshold, total));
     }
@@ -68,25 +71,24 @@ impl<F: PrimeField> Shares<F> {
 pub mod tests {
     use super::*;
     use crate::common::Share;
-    use ark_bls12_381::Bls12_381;
-    use ark_ec::pairing::Pairing;
+    use ark_bls12_381::{Bls12_381, Fr};
     use ark_serialize::{CanonicalDeserialize, CanonicalSerialize};
     use ark_std::rand::{rngs::StdRng, SeedableRng};
     use test_utils::test_serialization;
 
-    type Fr = <Bls12_381 as Pairing>::ScalarField;
-
     #[test]
     fn shamir_secret_sharing() {
         let mut rng = StdRng::seed_from_u64(0u64);
 
+        assert!(deal_random_secret::<_, Fr>(&mut rng, 1, 1).is_err());
         assert!(deal_random_secret::<_, Fr>(&mut rng, 5, 4).is_err());
 
         for (threshold, total) in vec![
             (2, 2),
             (2, 3),
             (2, 4),
             (2, 5),
+            (1, 3),
             (3, 3),
             (3, 4),
             (3, 5),

utils/README.md

@@ -0,0 +1,8 @@
+<!-- cargo-rdme start -->
+
+A collection of utilities used by our other crypto libraries. Some examples are Pedersen commitment,
+Elgamal encryption, some finite field utilities like inner product, weighted inner product, hadamard product,
+etc, multiscalar multiplication (MSM) like Fixed Base MSM, polynomial utilities like multiplying polynomials,
+creating polynomial from roots, etc, efficient way of checking several pairing relations in a single multi-pairing.
+
+<!-- cargo-rdme end -->

utils/src/commitment.rs

@@ -8,7 +8,7 @@ use digest::Digest;
 use serde::{Deserialize, Serialize};
 use serde_with::serde_as;
 
-/// A Pedersen commitment key. The Pedersen commitment will be `g * m + h * r` with opening `(m, r)`
+/// A Pedersen commitment key `(g, h)`. The Pedersen commitment will be `g * m + h * r` with opening `(m, r)`
 #[serde_as]
 #[derive(
     Clone, PartialEq, Eq, Debug, CanonicalSerialize, CanonicalDeserialize, Serialize, Deserialize,

utils/src/lib.rs

@@ -1,3 +1,9 @@
+//! A collection of utilities used by our other crypto libraries. Some examples are Pedersen commitment,
+//! Elgamal encryption, some finite field utilities like inner product, weighted inner product, hadamard product,
+//! etc, multiscalar multiplication (MSM) like Fixed Base MSM, polynomial utilities like multiplying polynomials,
+//! creating polynomial from roots, etc, efficient way of checking several pairing relations in a single multi-pairing.
+//!
+
 #![cfg_attr(not(feature = "std"), no_std)]
 
 extern crate alloc;
@@ -9,18 +15,30 @@ pub mod extend_some;
 #[macro_use]
 pub mod serde_utils;
 pub mod ecies;
+
+/// Elgamal encryption
 pub mod elgamal;
+
+/// Finite field utilities like inner product, weighted inner product, hadamard product, etc
 #[macro_use]
 pub mod ff;
+
+/// Pedersen commitment
 pub mod commitment;
+
+/// Hashing utilities like hashing arbitrary bytes to field element or group element
 pub mod hashing_utils;
 pub mod iter;
 pub mod macros;
 pub mod misc;
+/// Multiscalar multiplication (MSM) like Fixed Base MSM
 pub mod msm;
 pub mod owned_pairs;
 pub mod pairs;
+/// Polynomial utilities like multiplying polynomials, creating polynomial from roots, etc
 pub mod poly;
+/// An efficient way to check several equality relations involving pairings by combining the relations
+/// in a random linear combination and doing a multi-pairing check. Relies on Schwartz–Zippel lemma.
 pub mod randomized_pairing_check;
 pub mod signature;
 pub mod transcript;

utils/src/macros.rs

@@ -216,6 +216,7 @@ macro_rules! try_pairs {
     };
 }
 
+/// Return `$error` if `$left` not equals `$right`
 #[macro_export]
 macro_rules! expect_equality {
     ($left: expr, $right: expr, $error: expr) => {
@@ -225,13 +226,15 @@ macro_rules! expect_equality {
     };
 }
 
+/// Return pairing where `$pairing_func` is the pairing function, `$g1` is/are group G1 elements and `$g2` is/are group G2 elements
 #[macro_export]
 macro_rules! pair_g1_g2 {
     ($pairing_func: path, $g1: expr, $g2: expr) => {
         $pairing_func($g1, $g2)
     };
 }
 
+/// Return pairing where `$pairing_func` is the pairing function, `$g1` is/are group G1 elements and `$g2` is/are group G2 elements
 #[macro_export]
 macro_rules! pair_g2_g1 {
     ($pairing_func: path, $g2: expr, $g1: expr) => {

utils/src/transcript.rs

@@ -1,3 +1,5 @@
+//! Merlin transcripts
+
 use ark_ec::AffineRepr;
 use ark_ff::fields::Field;
 use ark_serialize::{CanonicalDeserialize, CanonicalSerialize};