Ian Goldberg 3 years ago
parent
commit
921ec26068
3 changed files with 49 additions and 3 deletions
  1. 1 0
      Cargo.toml
  2. 1 0
      src/lib.rs
  3. 47 3
      src/vss.rs

+ 1 - 0
Cargo.toml

@@ -7,3 +7,4 @@ edition = "2018"
 [dependencies]
 
 curve25519-dalek = "1"
+rand = "0.6"

+ 1 - 0
src/lib.rs

@@ -1,4 +1,5 @@
 extern crate curve25519_dalek;
+extern crate rand;
 
 pub mod vss;
 

+ 47 - 3
src/vss.rs

@@ -1,15 +1,59 @@
 use curve25519_dalek::edwards::EdwardsPoint;
 use curve25519_dalek::scalar::Scalar;
+use curve25519_dalek::constants::ED25519_BASEPOINT_POINT;
+use rand::rngs::ThreadRng;
 
 pub type Secret = Scalar;
 
-pub struct Share {}
+pub struct Share {
+    index: u32,
+    value: Scalar,
+}
 
-pub struct Commitment {}
+pub struct Commitment {
+    coms: Vec<EdwardsPoint>,
+}
 
 /// Create secret shares for a given secret.
 pub fn generate_shares(secret: Secret, numshares: u32, threshold: u32) -> Result<(Commitment, Vec<Share>), &'static str> {
-    unimplemented!("Not yet implemented")
+    if threshold < 1 { return Err("Threshold cannot be 0") }
+    if numshares < 1 { return Err("Number of shares cannot be 0") }
+    if threshold > numshares { return Err("Threshold cannot exceed numshares") }
+
+    let numcoeffs = (threshold-1) as usize;
+
+    let mut coeffs: Vec<Scalar> = Vec::with_capacity(numcoeffs);
+
+    let mut rng: ThreadRng = rand::thread_rng();
+
+    let mut shares: Vec<Share> = Vec::with_capacity(numshares as usize);
+
+    let mut comm: Commitment = Commitment { coms: Vec::with_capacity(threshold as usize) };
+
+    for _ in 1..numcoeffs {
+        coeffs.push(Scalar::random(&mut rng));
+    }
+
+    for share_index in 1..numshares {
+        // Evaluate the polynomial with `secret` as the constant term
+        // and `coeffs` as the other coefficients at the point x=share_index
+        // using Horner's method
+        let scalar_index = Scalar::from(share_index);
+        let mut value = Scalar::zero();
+        for i in (0..numcoeffs-1).rev() {
+            value += coeffs[i];
+            value *= scalar_index;
+        }
+        value += secret;
+        shares.push(Share{ index: share_index, value: value });
+    }
+
+    comm.coms.push(ED25519_BASEPOINT_POINT * secret);
+    for c in coeffs {
+        comm.coms.push(ED25519_BASEPOINT_POINT * c);
+    }
+
+    Ok((comm, shares))
 }
 
 /// Verify that a share is consistent with a commitment.