Shamir's secret sharing algorithm

shamir-secret-sharing/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+edition = "2021"
+name = "shamir-secret-sharing"
+version = "0.1.0"
+
+[dependencies]
+polynomial = {path = "../polynomial"}
+rand = "0.8.5"
+rand_chacha = "0.3.1"

shamir-secret-sharing/src/lib.rs

@@ -0,0 +1,44 @@
+#[cfg(test)]
+mod tests {
+    use polynomial::Polynomial;
+    use rand::prelude::*;
+
+    #[test]
+    fn shamir_secret_sharing() {
+        // Let's say we want to create a shamir secret scheme
+        // for hiding S = 119
+        let secret = 119;
+
+        // Assume that we want to break secret into 4 "parts",
+        // of which any 2 should be able to reconstruct the
+        // original secret
+        let parts = 4;
+        let threshold = 2;
+
+        // Hence, coefficients will be of form `secret + r1*x + r2*x^2...`
+        // where `r` is random values from `(0, threshold)`
+        let mut rng = rand_chacha::ChaCha8Rng::seed_from_u64(3091);
+        let coeffs: Vec<i64> = [secret]
+            .into_iter()
+            .chain((0..threshold).map(|_| rng.next_u32() as i64))
+            .collect();
+
+        let polynomial = Polynomial::new_from_coeffs(&coeffs);
+
+        // Ensure that we can get the secret back given we evaluate
+        // at 0
+        assert_eq!(polynomial.eval(0), secret);
+
+        // Now evaulate at a few random points to make the secret
+        let secret_parts: Vec<(i64, i64)> = (0..threshold)
+            .map(|_| {
+                let point_of_eval = rng.next_u32() as i64;
+                let eval = polynomial.eval(point_of_eval);
+                (point_of_eval, eval)
+            })
+            .collect();
+
+        // Ensure reconstruction is possible
+        // let reconstructed_poly = Polynomial::new_from_evalutations()
+    }
+}