feat: new ChameleonHash Helper

Author: twsc-james

EccSDK/ChameleonHashHelper.cs

@@ -0,0 +1,34 @@
+using EccGrpcSDK.models;
+using Org.BouncyCastle.Math;
+using Org.BouncyCastle.Math.EC;
+
+namespace EccGrpcSDK;
+
+public class ChameleonHashHelper
+{
+    // Kn = public key
+    // kn = private key
+    
+    public static BigInteger Sign(ChameleonHashRequest request)
+    {
+        // sign = (sessionKey - dn) mod n
+        // dn = H(m) * kn
+        var msgHash = HashHelper.Sha256(request.Message);
+        var dn = msgHash.Multiply(request.KeyPair.PrivateKey);
+        return request.SessionKey.Add(dn).Mod(request.Order);
+    }
+    
+    public static bool Verify(ChameleonHashRequest request, ECPoint rightChameleonHash)
+    {
+        return GetChameleonHash(request).Equals(rightChameleonHash);
+    }
+
+    private static ECPoint GetChameleonHash(ChameleonHashRequest request)
+    {
+        // chameleonHash = [Kn x H(m)] + [P x sessionKey]
+        var msgHash = HashHelper.Sha256(request.Message);
+        var rP = request.KeyPair.BasePoint.Multiply(request.Signature);
+        var chameleonHash = request.KeyPair.PublicKey.Multiply(msgHash).Add(rP).Normalize();
+        return chameleonHash;
+    }
+}

EccSDK/EccGenerator.cs

@@ -18,11 +18,13 @@ public KeyPair GenerateKeyPair(int keySize)
         var privateKey = (ECPrivateKeyParameters) keyGen.Private;
         var publicKey = (ECPublicKeyParameters) keyGen.Public;
 
-        return new KeyPair()
+        var generateKeyPair = new KeyPair()
         {
             PublicKey = publicKey.Q, 
             PrivateKey = privateKey.D,
             BasePoint = publicKey.Parameters.G
         };
+        
+        return generateKeyPair;
     }
 }

EccSDK/models/ChameleonHashRequest.cs

@@ -0,0 +1,12 @@
+using Org.BouncyCastle.Math;
+
+namespace EccGrpcSDK.models;
+
+public class ChameleonHashRequest
+{
+    public KeyPair KeyPair { get; set; }
+    public string Message { get; set; }
+    public BigInteger SessionKey { get; set; }
+    public BigInteger Order { get; set; }
+    public BigInteger Signature { get; set; }
+}