implement tally proof generation and tally proof verification

rust/catalyst-voting/src/crypto/elgamal.rs

@@ -27,6 +27,14 @@ impl Deref for SecretKey {
     }
 }
 
+impl Deref for PublicKey {
+    type Target = GroupElement;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
 impl SecretKey {
     /// Generate a random `SecretKey` value from the random number generator.
     pub fn generate<R: CryptoRngCore>(rng: &mut R) -> Self {

rust/catalyst-voting/src/crypto/zk_dl_equality.rs

@@ -10,8 +10,6 @@
 //! points `point_1` and `point_2`. The witness, on the other hand
 //! is the discrete logarithm, `dlog`.
 
-#![allow(dead_code, unused_variables)]
-
 use curve25519_dalek::digest::Update;
 
 use super::{
@@ -41,10 +39,8 @@ pub fn verify_dleq_proof(
     proof: &DleqProof, base_1: &GroupElement, base_2: &GroupElement, point_1: &GroupElement,
     point_2: &GroupElement,
 ) -> bool {
-    let r1 = base_1 * &proof.1;
-    let r2 = base_2 * &proof.1;
-    let a_1 = &r1 - &(point_1 * &proof.0);
-    let a_2 = &r2 - &(point_2 * &proof.0);
+    let a_1 = &(base_1 * &proof.1) - &(point_1 * &proof.0);
+    let a_2 = &(base_2 * &proof.1) - &(point_2 * &proof.0);
 
     let challenge = calculate_challenge(base_1, base_2, point_1, point_2, &a_1, &a_2);
     challenge == proof.0

rust/catalyst-voting/src/tally/proof.rs

@@ -1,15 +1,56 @@
 //! Tally proof generation and verification procedures.
 //! It allows to transparently verify the correctness of decryption tally procedure.
 
+use std::ops::Mul;
+
 use rand_core::CryptoRngCore;
 
 use super::EncryptedTally;
-use crate::SecretKey;
+use crate::{
+    crypto::{
+        group::{GroupElement, Scalar},
+        zk_dl_equality::{generate_dleq_proof, verify_dleq_proof, DleqProof},
+    },
+    PublicKey, SecretKey,
+};
+
+/// Tally proof struct.
+#[allow(clippy::module_name_repetitions)]
+pub struct TallyProof(DleqProof);
 
 /// Generates a tally proof.
 /// More detailed described [here](https://input-output-hk.github.io/catalyst-voices/architecture/08_concepts/voting_transaction/crypto/#tally-proof)
 #[allow(clippy::module_name_repetitions)]
 pub fn generate_tally_proof<R: CryptoRngCore>(
-    _tally_result: &EncryptedTally, _secret_key: &SecretKey, _rng: &mut R,
-) {
+    encrypted_tally: &EncryptedTally, secret_key: &SecretKey, rng: &mut R,
+) -> TallyProof {
+    let randomness = Scalar::random(rng);
+    let e1 = encrypted_tally.0.first();
+    let d = e1.mul(secret_key);
+
+    let proof = generate_dleq_proof(
+        &GroupElement::GENERATOR,
+        e1,
+        &secret_key.public_key(),
+        &d,
+        secret_key,
+        &randomness,
+    );
+
+    TallyProof(proof)
+}
+
+/// Verifies a tally proof.
+/// More detailed described [here](https://input-output-hk.github.io/catalyst-voices/architecture/08_concepts/voting_transaction/crypto/#tally-proof)
+#[must_use]
+#[allow(clippy::module_name_repetitions)]
+pub fn verify_tally_proof(
+    encrypted_tally: &EncryptedTally, tally: u64, public_key: &PublicKey, proof: &TallyProof,
+) -> bool {
+    let tally = Scalar::from(tally);
+    let e1 = encrypted_tally.0.first();
+    let e2 = encrypted_tally.0.second();
+    let d = &GroupElement::GENERATOR.mul(&tally) - e2;
+
+    verify_dleq_proof(&proof.0, &GroupElement::GENERATOR, e1, public_key, &d)
 }