Reading binary from table column into byte[] array

Question

I'm using PBKDF2 in my application to store users passwords. In my Users table, I have a Salt and Password column which is determined like this:

// Hash the users password using PBKDF2
var DeriveBytes = new Rfc2898DeriveBytes(_Password, 20);
byte[] _Salt = DeriveBytes.Salt;
byte[] _Key = DeriveBytes.GetBytes(20);  // _Key is put into the Password column

On my login page I need to retrieve this salt and password. Because they're byte[] arrays, I store them in my table as varbinary(MAX). Now I need to retrieve them to compare against the users entered password. How would I do that using SqlDataReader? At the moment I have this:

cn.Open();
SqlCommand Command = new SqlCommand("SELECT Salt, Password FROM Users WHERE Email = @Email", cn);
Command.Parameters.Add("@Email", SqlDbType.NVarChar).Value = _Email;
SqlDataReader Reader = Command.ExecuteReader(CommandBehavior.CloseConnection);
Reader.Read();
if (Reader.HasRows)
{
    // This user exists, check their password with the one entered
    byte[] _Salt = Reader.GetBytes(0, 0, _Salt, 0, _Salt.Length);
}
else
{
    // No user with this email exists
    Feedback.Text = "No user with this email exists, check for typos or register";
}

But I know for a fact that it's wrong. Other methods in Reader have only one parameter being the index of the column to retrieve.

Answer 1

Casting it directly to a byte[] has worked for me so far.

using (SqlConnection c = new SqlConnection("FOO"))
{
    c.Open();
    String sql = @"
        SELECT Salt, Password 
        FROM Users 
        WHERE (Email = @Email)";
    using (SqlCommand cmd = new SqlCommand(sql, c))
    {
        cmd.Parameters.Add("@Email", SqlDbType.NVarChar).Value = _Email;
        using (SqlDataReader d = cmd.ExecuteReader())
        {
            if (d.Read())
            {
                byte[] salt = (byte[])d["Salt"];
                byte[] pass = (byte[])d["Password"];

                //Do stuff with salt and pass
            }
            else
            {
                // NO User with email exists
            }
        }
    }
}

Answer 2

I'm not sure why you think the code you wrote is wrong (please explain). But specifically for the error:
Notice that GetBytes returns a long not a byte array.

So, you should use: Reader.GetBytes(0, 0, _Salt, 0, _Salt.Length);

or
long bytesRead = Reader.GetBytes(0, 0, _Salt, 0, _Salt.Length);