Merge pull request #15 from h5p9sl/master

Fixed RNG generating null-bytes in metadata; causing read errors.

Crypto Notepad/AES.cs

@@ -83,12 +83,43 @@ public bool GetMetadata(byte[] rawData)
 
     class AES
     {
+        private static bool ByteArrayIsNonZero(byte[] byte_array)
+        {
+            foreach (byte i in byte_array)
+            {
+                if (i == 0)
+                {
+                    return false;
+                }
+            }
+            return true;
+        }
+
+        // The purpose of this function is to ensure that the bytes generated by it are nonzero 100% of the time
+        // as there was a strange bug in which RNGCryptoServiceProvider.GetNonZeroBytes() would return a null byte sometimes
+        private static byte[] GenerateSecureNonZeroByteArray(int length)
+        {
+            byte[] result = new byte[length];
+
+            using (RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider())
+            {
+                do
+                {
+                    rng.GetNonZeroBytes(result);
+                } while (!ByteArrayIsNonZero(result));
+            }
+
+            return result;
+        }
+
         public static string Encrypt(string plainText, string password,
         string salt = null, string hashAlgorithm = "SHA1",
         int passwordIterations = 2, int keySize = 256)
         {
             if (string.IsNullOrEmpty(plainText))
-                return "";
+                return null;
+            if (string.IsNullOrEmpty(password))
+                return null;
 
             byte[] plainTextBytes;
             byte[] saltValueBytes;
@@ -97,9 +128,7 @@ public static string Encrypt(string plainText, string password,
             if (string.IsNullOrEmpty(salt))
             {
                 saltValueBytes = new byte[64]; // Nice and long
-                RandomNumberGenerator rng = RandomNumberGenerator.Create();
+                saltValueBytes = GenerateSecureNonZeroByteArray(saltValueBytes.Length);
-                rng.GetNonZeroBytes(saltValueBytes);
-                rng.Dispose();
             }
             else
             {
@@ -117,7 +146,9 @@ public static string Encrypt(string plainText, string password,
             byte[] keyBytes = derivedPassword.GetBytes(keySize / 8);
             RijndaelManaged symmetricKey = new RijndaelManaged();
             symmetricKey.Mode = CipherMode.CBC;
-            symmetricKey.GenerateIV();
+
+            // Generate IV
+            symmetricKey.IV = GenerateSecureNonZeroByteArray(symmetricKey.IV.Length);
 
             byte[] cipherTextBytes = null;
 
@@ -151,6 +182,8 @@ public static string Decrypt(string cipherText, string password, string salt = "
         {
             if (string.IsNullOrEmpty(cipherText))
                 return null;
+            if (string.IsNullOrEmpty(password))
+                return null;
 
             byte[] initialVectorBytes;
             byte[] saltValueBytes;