Encrypt is a simple class incorporating several encryption/decryption functions. It does not rely on CryptoAPI or any encryption packs and will work everywhere. The last Encrypt function (the one that works with files) is standalone. I made it operate in a stream-like manner, without reading the whole file into memory, which makes it possible to encrypt/decrypt gigabytes of data without going out of memory space. I would like to encourage you to read through it and understand how it works, it should be pretty easy.”]
Source: https://www.codeproject.com/Articles/5719/Simple-encrypting-and-decrypting-data-in-C