Encrypt a BMP file

Proposed exercise

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Create a program to encrypt/decrypt a BMP image file, by changing the "BM" mark in the first two bytes with MB and vice versa.

Use the advanced FileStream constructor to allow simultaneous reading and writing.

Output

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Solution

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using System;
using System.IO;

class EncryptBMP
{
static void Main()
{
Console.Write("Enter the name: ");
string name = Console.ReadLine();

if (!File.Exists(name))
{
Console.WriteLine("Not exists");
return;
}

try
{
FileStream file = File.Open(name, 
FileMode.Open,FileAccess.ReadWrite);
byte b1 = (byte)file.ReadByte();
byte b2 = (byte)file.ReadByte();

if ((Convert.ToChar(b1) != 'B')
|| (Convert.ToChar(b2) != 'M'))
Console.WriteLine("not bmp valid");
else
{
file.Seek(0, SeekOrigin.Begin);
file.WriteByte((byte)'M');
file.WriteByte((byte)'B');
}
file.Close();
}
catch (Exception)
{
Console.WriteLine("Error");
}
}
}