I am having some problems in using CryptoStream when I want to encrypt a binary stream after binary serialization and save it to a file. I am getting the following exception

System.ArgumentException : Stream was not readable.

Can anybody please show me how to encrypt a binary stream and save it to a file and deserialize it back correctly?

The code is as follows:

class Program
    {
        public static void Main(string[] args)
        {
            var b = new B {Name = "BB"};
            WriteFile<B>(@"C:\test.bin", b, true);
            var bb = ReadFile<B>(@"C:\test.bin", true);

            Console.WriteLine(b.Name == bb.Name);
            Console.ReadLine();
        }

        public static T ReadFile<T>(string file, bool decrypt)
        {
            T bObj = default(T);
            var _binaryFormatter = new BinaryFormatter();
            Stream buffer = null;

            using (var stream = new FileStream(file, FileMode.OpenOrCreate))
            {
                if(decrypt)
                {
                    const string strEncrypt = "*#4$%^.++q~!cfr0(_!#$@$!&#&#*&@(7cy9rn8r265&$@&*E^184t44tq2cr9o3r6329";
                    byte[] dv = {0x12, 0x34, 0x56, 0x78, 0x90, 0xAB, 0xCD, 0xEF};
                    CryptoStream cs;
                    DESCryptoServiceProvider des = null;

                    var byKey = Encoding.UTF8.GetBytes(strEncrypt.Substring(0, 8));
                    using (des = new DESCryptoServiceProvider())
                    {
                        cs = new CryptoStream(stream, des.CreateEncryptor(byKey, dv), CryptoStreamMode.Read);
                    }
                    buffer = cs;
                }
                else
                    buffer = stream;
                try
                {
                    bObj = (T) _binaryFormatter.Deserialize(buffer);
                }
                catch(SerializationException ex)
                {
                    Console.WriteLine(ex.Message);
                }
            }

            return bObj;
        }

        public static void WriteFile<T>(string file, T bObj, bool encrypt)
        {
            var _binaryFormatter = new BinaryFormatter();
            Stream buffer;

            using (var stream = new FileStream(file, FileMode.Create))
            {
                try
                {
                    if(encrypt)
                    {
                        const string strEncrypt = "*#4$%^.++q~!cfr0(_!#$@$!&#&#*&@(7cy9rn8r265&$@&*E^184t44tq2cr9o3r6329";
                        byte[] dv = {0x12, 0x34, 0x56, 0x78, 0x90, 0xAB, 0xCD, 0xEF};
                        CryptoStream cs;
                        DESCryptoServiceProvider des = null;

                        var byKey = Encoding.UTF8.GetBytes(strEncrypt.Substring(0, 8));
                        using (des = new DESCryptoServiceProvider())
                        {
                            cs = new CryptoStream(stream, des.CreateEncryptor(byKey, dv), CryptoStreamMode.Write);
                            buffer = cs;
                        }
                    }
                    else
                        buffer = stream;

                    _binaryFormatter.Serialize(buffer, bObj);
                    buffer.Flush();
                }
                catch(SerializationException ex)
                {
                    Console.WriteLine(ex.Message);
                }
            }
        }
    }

    [Serializable]
    public class B
    {
        public string Name {get; set;}
    }

It throws the serialization exception as follows

The input stream is not a valid binary format. The starting contents (in bytes) are: 3F-17-2E-20-80-56-A3-2A-46-63-22-C4-49-56-22-B4-DA ...