Create RemoteServerMock (oracle), refactor

Author: hckr

Program.cs

@@ -7,18 +7,23 @@ namespace Padding_Oracle_Attack
 {
     class PaddingOracleAttack
     {
+        private static RemoteServerMock server = new RemoteServerMock();
         public static void Main()
         {
             string hiddenMessage = "I'd just like to interject for a moment. What you’re referring to as Linux, is in fact, GNU/Linux, or as I’ve recently taken to calling it, GNU plus Linux.";
 
             using (Aes aes = Aes.Create())
             {
-                byte[] encrypted = EncryptStringToBytes_Aes(hiddenMessage);
+                byte[] encrypted = server.Encrypt(hiddenMessage);
                 var blocks = sliceBytesIntoBlocks(encrypted);
 
                 Console.WriteLine("Plaintext:\n{0}", hiddenMessage);
                 Console.WriteLine("\nCiphertext:\n{0}", String.Join("\n", blocks.ConvertAll(block => Convert.ToBase64String(block))));
                 Console.WriteLine("\nAttack results:\nTODO");
+
+                encrypted[encrypted.Length - 1] = 22;
+
+                Console.WriteLine("\nPadding is {0}", server.IsPaddingCorrect(encrypted) ? "correct" : "incorrect");
             }
         }
 
@@ -35,75 +40,5 @@ static List<byte[]> sliceBytesIntoBlocks(byte[] bytes, int blockSizeBytes = 16)
 
             return blocks;
         }
-        static byte[] EncryptStringToBytes_Aes(string plainText)
-        {
-            byte[] encrypted;
-
-            using (Aes aesAlg = Aes.Create())
-            {
-                aesAlg.Mode = CipherMode.CBC;
-                aesAlg.Padding = PaddingMode.PKCS7;
-
-                ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);
-
-                using (MemoryStream msEncrypt = new MemoryStream())
-                {
-                    using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
-                    {
-                        using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
-                        {
-                            swEncrypt.Write(plainText);
-                        }
-                        encrypted = msEncrypt.ToArray();
-                    }
-                }
-            }
-
-            return encrypted;
-        }
-
-        static string DecryptStringFromBytes_Aes(byte[] cipherText, byte[] Key, byte[] IV)
-        {
-            // Check arguments.
-            if (cipherText == null || cipherText.Length <= 0)
-                throw new ArgumentNullException("cipherText");
-            if (Key == null || Key.Length <= 0)
-                throw new ArgumentNullException("Key");
-            if (IV == null || IV.Length <= 0)
-                throw new ArgumentNullException("IV");
-
-            // Declare the string used to hold
-            // the decrypted text.
-            string plaintext = null;
-
-            // Create an Aes object
-            // with the specified key and IV.
-            using (Aes aesAlg = Aes.Create())
-            {
-                aesAlg.Key = Key;
-                aesAlg.IV = IV;
-
-                // Create a decryptor to perform the stream transform.
-                ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV);
-
-                // Create the streams used for decryption.
-                using (MemoryStream msDecrypt = new MemoryStream(cipherText))
-                {
-                    using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))
-                    {
-                        using (StreamReader srDecrypt = new StreamReader(csDecrypt))
-                        {
-
-                            // Read the decrypted bytes from the decrypting stream
-                            // and place them in a string.
-                            plaintext = srDecrypt.ReadToEnd();
-                        }
-                    }
-                }
-
-            }
-
-            return plaintext;
-        }
     }
 }

RemoteServerMock.cs

@@ -0,0 +1,64 @@
+using System.IO;
+using System.Security.Cryptography;
+
+namespace Padding_Oracle_Attack
+{
+    class RemoteServerMock
+    {
+        private Aes aesAlg = Aes.Create();
+
+        public RemoteServerMock()
+        {
+            aesAlg.BlockSize = 128;
+            aesAlg.Mode = CipherMode.CBC;
+            aesAlg.Padding = PaddingMode.PKCS7;
+        }
+
+        public byte[] Encrypt(string plaintext)
+        {
+            byte[] encrypted;
+
+            ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);
+
+            using (MemoryStream msEncrypt = new MemoryStream())
+            {
+                using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
+                {
+                    using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
+                    {
+                        swEncrypt.Write(plaintext);
+                    }
+                    encrypted = msEncrypt.ToArray();
+                }
+            }
+
+            return encrypted;
+        }
+
+        public bool IsPaddingCorrect(byte[] ciphertext)
+        {
+            try
+            {
+                ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV);
+
+                using (MemoryStream msDecrypt = new MemoryStream(ciphertext))
+                {
+                    using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))
+                    {
+                        using (StreamReader srDecrypt = new StreamReader(csDecrypt))
+                        {
+                            srDecrypt.ReadToEnd();
+                        }
+
+                    }
+                }
+            }
+            catch (CryptographicException)
+            {
+                return false;
+            }
+
+            return true;
+        }
+    }
+}