Add ZK feature

Cargo.toml

@@ -11,7 +11,7 @@ exclude = [".github/workflows/dusk-ci.yml", ".gitignore"]
 [dependencies]
 rand_core = { version = "0.6", default-features = false }
 dusk-bytes = "0.1"
-dusk-plonk = { version = "0.19", default-features = false }
+dusk-plonk = { version = "0.19", default-features = false, optional = true }
 dusk-bls12_381 = { version = "0.13", default-features = false }
 bls12_381-bls = { version = "0.3", default-features = false }
 dusk-jubjub = { version = "0.14", default-features = false, features = ["zeroize"] }
@@ -41,3 +41,6 @@ rkyv-impl = [
     "rkyv",
     "bytecheck"
 ]
+zk = [
+    "dusk-plonk",
+]

src/encryption/elgamal.rs

@@ -10,6 +10,8 @@
 //! Reference: https://link.springer.com/chapter/10.1007/3-540-39568-7_2
 
 use dusk_jubjub::{JubJubExtended, JubJubScalar, GENERATOR};
+
+#[cfg(feature = "zk")]
 use dusk_plonk::prelude::*;
 
 /// Encrypts a JubJubExtended plaintext given a public key and a fresh random
@@ -37,6 +39,7 @@ pub fn decrypt(
 
 /// Encrypt in-circuit a plaintext, returning
 /// a ciphertext (WitnessPoint, WitnessPoint)
+#[cfg(feature = "zk")]
 pub fn zk_encrypt(
     composer: &mut Composer,
     public_key: &JubJubAffine,

tests/encryption.rs

@@ -5,15 +5,19 @@
 // Copyright (c) DUSK NETWORK. All rights reserved.
 
 use dusk_jubjub::{JubJubAffine, JubJubScalar, GENERATOR, GENERATOR_EXTENDED};
-use dusk_plonk::prelude::*;
 use ff::Field;
 use rand_core::OsRng;
 
 use phoenix_core::{aes, elgamal, PublicKey, SecretKey};
 
+#[cfg(feature = "zk")]
+use dusk_plonk::prelude::*;
+#[cfg(feature = "zk")]
 static LABEL: &[u8; 12] = b"dusk-network";
+#[cfg(feature = "zk")]
 const CAPACITY: usize = 12; // capacity required for the setup
 
+#[cfg(feature = "zk")]
 #[derive(Default, Debug)]
 pub struct ElGamalCircuit {
     public_key: JubJubAffine,
@@ -23,6 +27,7 @@ pub struct ElGamalCircuit {
     ciphertext_2: JubJubAffine,
 }
 
+#[cfg(feature = "zk")]
 impl ElGamalCircuit {
     pub fn new(
         public_key: &JubJubExtended,
@@ -41,6 +46,7 @@ impl ElGamalCircuit {
     }
 }
 
+#[cfg(feature = "zk")]
 impl Circuit for ElGamalCircuit {
     fn circuit(&self, composer: &mut Composer) -> Result<(), Error> {
         let (ciphertext_1, ciphertext_2) = elgamal::zk_encrypt(
@@ -96,6 +102,7 @@ fn test_elgamal_encrypt_and_decrypt() {
     assert_ne!(message, dec_message_wrong);
 }
 
+#[cfg(feature = "zk")]
 #[test]
 fn test_elgamal_zk_encrypt() {
     let sk = SecretKey::random(&mut OsRng);