Merge pull request CS-3372-Anonymous-Credential-Experiment#2 from CS-3372-Anonymous-Credential-Experiment/adding_iss

adding iss

Author: DTJ-Tran

src/issuer.rs

@@ -0,0 +1,57 @@
+use bbs_plus::prelude::SecretKey;
+use num_bigint::BigUint;
+use ark_bls12_381::{
+    Fr,
+    g1::{G1_GENERATOR_X, G1_GENERATOR_Y},
+    G1Affine, G1Projective
+};
+use rand::thread_rng;
+use sha2::{Sha256};
+use num_bigint::RandBigInt;
+use ark_ec::AffineRepr;
+use ark_ff::PrimeField;
+use std::ops::Mul;
+
+#[allow(dead_code)]
+pub struct Issuer {
+    q: BigUint, // Security Parameter
+    sk: SecretKey<Fr>,
+    tau: BigUint, // Trapdoor values (secret)
+    pub g1: G1Projective,
+
+}
+
+impl Issuer { // Assume the issuer can work with Groth-Sahai Commitment (which now is not support) 
+    // currently: all the secret x shall be stored off-chain & accepting the risk of linkability on user's identity trade-off 
+    // for revocability with perdersen commitment
+    pub fn new() -> Self { // Initialization
+        let g1_affine = G1Affine::new_unchecked(G1_GENERATOR_X, G1_GENERATOR_Y);
+        let g1 = g1_affine.into_group(); // Into G1Projective
+        let q = BigUint::from(Fr::MODULUS);  // get the security parameter = 2 * 128 = 256 bits
+        let mut rng = thread_rng();
+        let seed_big = rng.gen_biguint_below(&q);
+        let seed_bytes = seed_big.to_bytes_le();
+        let sk = SecretKey::<Fr>::generate_using_seed::<Sha256>(&seed_bytes);
+        // geneerate the tau
+        let tau = rng.gen_biguint_below(&q); // Sample from field Z_q
+
+        Self {
+            q: q,
+            sk: sk,
+            tau: tau,
+            g1:g1
+        }
+
+    }
+    pub fn get_com_key(&self) -> (G1Projective, G1Projective) {
+        let g = self.g1;
+        let tau_fr = Fr::from_le_bytes_mod_order(&self.tau.to_bytes_le());
+        let h = g.mul(tau_fr);
+        (g, h)
+    }
+    pub fn get_tau_fr(&self) -> Fr {
+        Fr::from_le_bytes_mod_order(&self.tau.to_bytes_le())
+    }
+}
+
+