C# - How to encrypt a data dictionary

A simple way would be convert the dictionary to string by having 2 different delimiters inside.
One between key and its value and another between each key-value pair.
Example:
key1@value1|key2@value2|key3@value3

To convert dictionary to such representation:
String.Join("|", dictionary.Select(kv=>String.Format("{0}@{1}",kv.Key,kv.Value).ToArray());

U must choose delimiters that u know are not part of the dictionary keys or values otherwise u wont get the conversion right.
Next step is to encrypt the string.
To get dictionary back from the string:
var dictionary = str.Split('|').ToDictionary(s=>s.Split('@')[0],s=>s.Split('@')[1]);

I have created the encrypt file with the routine below. How would I read it back.
Do I first read all the bytes from CryptoStream. Then put into the memorystream, then read from memory stream and restore data into the dictionary.  Any help will appreciated

        public void EncryptAndSerialize(string filename, SymmetricAlgorithm key)
        {
            using (FileStream fs = File.Open(filename, FileMode.Create))
            {
                using (CryptoStream cs = new CryptoStream(fs, key.CreateEncryptor(), CryptoStreamMode.Write))
                {
                    using (MemoryStream ms = new MemoryStream())
                    {
                        foreach (var item in map)
                        {

                            string line = item.Key + "," + item.Value + "\n";
                            byte[] array = Encoding.ASCII.GetBytes(line);
                            ms.Write(array, 0, line.Length);
                        }
                        byte[] allbytes = ms.GetBuffer();
                        cs.Write(allbytes, 0, allbytes.Length);
                    }

                }
            }
        }

Thanks