Updates to DiffieHellman

sjh37 · Apr 11, 2018 · c31e74e · c31e74e
1 parent 9d09258
commit c31e74e
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Showing 4 changed files with 50 additions and 25 deletions.
diff --git a/DiffieHellman.cs b/DiffieHellman.cs
@@ -9,7 +9,6 @@ public sealed class DiffieHellman
         private readonly Aes _aes;
         private readonly ECDiffieHellmanCng _diffieHellman;
         public byte[] PublicKey { get; }
-        public byte[] IV => _aes.IV;
 
         public DiffieHellman()
         {
@@ -25,37 +24,30 @@ public DiffieHellman()
             PublicKey = _diffieHellman.PublicKey.ToByteArray();
         }
 
-        public byte[] Encrypt(byte[] publicKey, string secretMessage)
+        public byte[] Encrypt(DiffieHellman otherPerson, string secretMessage)
         {
-            byte[] encryptedMessage;
-            var key = CngKey.Import(publicKey, CngKeyBlobFormat.EccPublicBlob);
-            var derivedKey = _diffieHellman.DeriveKeyMaterial(key); // "Common secret"
-
-            _aes.Key = derivedKey;
+            // Common secret created by Diffie Hellman
+            _aes.Key = _diffieHellman.DeriveKeyMaterial(CngKey.Import(otherPerson.PublicKey, CngKeyBlobFormat.EccPublicBlob));
 
             using (var cipherText = new MemoryStream())
             {
                 using (var cs = new CryptoStream(cipherText, _aes.CreateEncryptor(), CryptoStreamMode.Write))
                 {
-                    var ciphertextMessage = Encoding.UTF8.GetBytes(secretMessage);
+                    var ciphertextMessage = Encoding.Unicode.GetBytes(secretMessage);
                     cs.Write(ciphertextMessage, 0, ciphertextMessage.Length);
                     cs.Close();
                 }
 
-                encryptedMessage = cipherText.ToArray();
+                return cipherText.ToArray();
             }
-
-            return encryptedMessage;
         }
 
-        public string Decrypt(byte[] publicKey, byte[] encryptedMessage, byte[] iv)
+        public string Decrypt(DiffieHellman otherPerson, byte[] encryptedMessage)
         {
-            string decryptedMessage;
-            var key = CngKey.Import(publicKey, CngKeyBlobFormat.EccPublicBlob);
-            var derivedKey = _diffieHellman.DeriveKeyMaterial(key);
-
-            _aes.Key = derivedKey;
-            _aes.IV = iv;
+            // Common secret created by Diffie Hellman
+            _aes.Key = _diffieHellman.DeriveKeyMaterial(CngKey.Import(otherPerson.PublicKey, CngKeyBlobFormat.EccPublicBlob));
+            var backupIV = _aes.IV;
+            _aes.IV = otherPerson._aes.IV;
 
             using (var plainText = new MemoryStream())
             {
@@ -65,10 +57,10 @@ public string Decrypt(byte[] publicKey, byte[] encryptedMessage, byte[] iv)
                     cs.Close();
                 }
 
-                decryptedMessage = Encoding.UTF8.GetString(plainText.ToArray());
-            }
+                _aes.IV = backupIV;
 
-            return decryptedMessage;
+                return Encoding.Unicode.GetString(plainText.ToArray());
+            }
         }
     }
 }
diff --git a/...less.Net.Encryption.Tests.Unit/Effortless.Net.Encryption.Tests.Unit/DiffieHellmanTests.cs b/...less.Net.Encryption.Tests.Unit/Effortless.Net.Encryption.Tests.Unit/DiffieHellmanTests.cs
@@ -8,18 +8,41 @@ public class DiffieHellmanTests
         [Test]
         public void Encrypt_Decrypt()
         {
-            var text = "Hello World!";
+            const string text = "Hello World!";
 
-            var bob = new DiffieHellman();
             var alice = new DiffieHellman();
+            var bob = new DiffieHellman();
 
             // Bob uses Alice's public key to encrypt his message.
-            var secretMessage = bob.Encrypt(alice.PublicKey, text);
+            var secretMessage = bob.Encrypt(alice, text);
 
             // Alice uses Bob's public key and IV to decrypt the secret message.
-            var decryptedMessage = alice.Decrypt(bob.PublicKey, secretMessage, bob.IV);
+            var decryptedMessage = alice.Decrypt(bob, secretMessage);
+            Assert.AreEqual(text, decryptedMessage);
+        }
+
+        [Test]
+        public void MultipleTests()
+        {
+            const string text = "Hello World!";
 
+            var alice = new DiffieHellman();
+            var bob = new DiffieHellman();
+
+            var secretMessageA = alice.Encrypt(bob, text);
+            var secretMessage1 = bob.Encrypt(alice, text);
+            var decryptedMessage = alice.Decrypt(bob, secretMessage1);
+            var secretMessageB = alice.Encrypt(bob, text);
             Assert.AreEqual(text, decryptedMessage);
+            Assert.AreEqual(secretMessageA, secretMessageB);
+
+            // See if its repeatable due to IV being replaced by previous decryption
+            var secretMessage2 = bob.Encrypt(alice, text);
+            decryptedMessage = alice.Decrypt(bob, secretMessage2);
+            Assert.AreEqual(text, decryptedMessage);
+
+            // Should be the same if nothing has changed
+            Assert.AreEqual(secretMessage1, secretMessage2);
         }
     }
 }
diff --git a/Effortless.Net.Encryption.csproj b/Effortless.Net.Encryption.csproj
@@ -56,6 +56,7 @@
     <Compile Include="Strings.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
     <None Include="Effortless.Net.Encryption.pfx" />
+    <None Include="README.md" />
   </ItemGroup>
   <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
 </Project>
diff --git a/README.md b/README.md
@@ -65,4 +65,13 @@ ds.AssignNewKey();
 var signature = ds.SignData(hash);
 var result = ds.VerifySignature(hash, signature);
 Assert.IsTrue(result);
+
+// Diffie Hellman
+var alice = new DiffieHellman();
+var bob = new DiffieHellman();
+// Bob uses Alice's public key to encrypt his message.
+var secretMessage = bob.Encrypt(alice, "Hello");
+// Alice uses Bob's public key and IV to decrypt the secret message.
+var decryptedMessage = alice.Decrypt(bob, secretMessage);
+Assert.AreEqual("Hello", decryptedMessage);
 ```