System.Security.Cryptography.CryptographicException: Wrong Key Length

When I started using this plugin for encryption purpose:

Secured PlayerPrefs

Now after run, I was getting this exclamation message in console, so its not working as per my thinking.

This is source code for encryption and decryption.

 static string Encrypt(string strPlain, string password)
     {
         if (!useSecure)
             return strPlain;
 
         try
         {
             DESCryptoServiceProvider des = new DESCryptoServiceProvider();
 
             Rfc2898DeriveBytes rfc2898DeriveBytes = new Rfc2898DeriveBytes(password, GetIV(), Iterations);
 
             byte[] key = rfc2898DeriveBytes.GetBytes(8);
 
             using (var memoryStream = new MemoryStream())
             using (var cryptoStream = new CryptoStream(memoryStream, des.CreateEncryptor(key, GetIV()), CryptoStreamMode.Write))
             {
                 memoryStream.Write(GetIV(), 0, GetIV().Length);
 
                 byte[] plainTextBytes = Encoding.UTF8.GetBytes(strPlain);
 
                 cryptoStream.Write(plainTextBytes, 0, plainTextBytes.Length);
                 cryptoStream.FlushFinalBlock();
 
                 return Convert.ToBase64String(memoryStream.ToArray());
             }
         }
         catch (Exception e)
         {
             Debug.LogWarning("Encrypt Exception: " + e);
             return strPlain;
         }
     }
 
     static string Decrypt(string strEncript, string password)
     {
         if (!useSecure)
             return strEncript;
 
         try
         {
             byte[] cipherBytes = Convert.FromBase64String(strEncript);
 
             using (var memoryStream = new MemoryStream(cipherBytes))
             {
                 DESCryptoServiceProvider des = new DESCryptoServiceProvider();
 
                 byte[] iv = GetIV();
                 memoryStream.Read(iv, 0, iv.Length);
 
                 // use derive bytes to generate key from password and IV
                 var rfc2898DeriveBytes = new Rfc2898DeriveBytes(password, iv, Iterations);
 
                 byte[] key = rfc2898DeriveBytes.GetBytes(8);
 
                 using (var cryptoStream = new CryptoStream(memoryStream, des.CreateDecryptor(key, iv), CryptoStreamMode.Read))
                 using (var streamReader = new StreamReader(cryptoStream))
                 {
                     string strPlain = streamReader.ReadToEnd();
                     return strPlain;
                 }
             }
         }
         catch (Exception e)
         {
             Debug.LogWarning("Decrypt Exception: " + e);
             return strEncript;
         }
 
     }

Please share your suggestion for this.