Make simple encryption software in C #

I made a simple encryption software in C #.

This time, it is a simple software that encrypts and decrypts the original text you want to encrypt using Key.
I’m using Xor.

If C is the encrypted data, O is the original data, and K is the key

C = O xor K

And encrypt

O = C xor K

You can decrypt it with.
It is an encryption that uses the nature of this Xor.

program

It’s organized into classes, so you can make it into a library or embed it.

code.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Ango
{
    class code
    {
        public string encrypt(string original,string key)
        {
            string str = original;
            byte[] arr = Encoding.GetEncoding("Shift_JIS").GetBytes(str);
            string str2 = key;
            byte[] arr2 = Encoding.GetEncoding("Shift_JIS").GetBytes(str2);

            string out_string = "";
            int str2_index = 0;
            int str2_next_index;

            for (int i = 0; i < arr.Length; i++)
            {
                str2_next_index = str2_index + 1;
                if (str2_next_index >= arr2.Length) str2_next_index = 0;

                arr2[str2_index] = (byte)((arr2[str2_index] + arr2[str2_next_index]) ^ arr2[str2_next_index]);
                arr2[str2_next_index] = (byte)(arr2[str2_index] + arr2[str2_next_index]);

                out_string = out_string + (arr[i] ^ arr2[str2_index]).ToString() + ",";

                str2_index++;
                if (str2_index >= arr2.Length) str2_index = 0;
            }

            return out_string;
        }

        public string decrypt(string cryptogram,string key)
        {
            string[] arr = cryptogram.Split(',');
            byte[] byte_arr = new byte[arr.Length];

            string str2 = key;
            byte[] arr2 = Encoding.GetEncoding("Shift_JIS").GetBytes(str2);

            int str2_index = 0;
            int str2_next_index;

            for (int i = 0; i < arr.Length - 1; i++)
            {
                str2_next_index = str2_index + 1;
                if (str2_next_index >= arr2.Length) str2_next_index = 0;

                arr2[str2_index] = (byte)((arr2[str2_index] + arr2[str2_next_index]) ^ arr2[str2_next_index]);
                arr2[str2_next_index] = (byte)(arr2[str2_index] + arr2[str2_next_index]);

                byte_arr[i] = Convert.ToByte(arr[i]);
                byte_arr[i] = (byte)(byte_arr[i] ^ arr2[str2_index]);

                str2_index++;
                if (str2_index >= arr2.Length) str2_index = 0;
            }


            string out_str = Encoding.GetEncoding("Shift_JIS").GetString(byte_arr);

            return out_str;
        }
    }
}

Commentary

The function ʻencrypt` encrypts.
Pass the original text and key as arguments.
The encrypted version is returned in text format.

First, change the original text and key from String to Byte [] .
Xor while shifting the two Byte [] by 1 byte.

With this alone, it seems that the key is easy to guess, so I am constantly changing the key.

                arr2[str2_index] = (byte)((arr2[str2_index] + arr2[str2_next_index]) ^ arr2[str2_next_index]);
                arr2[str2_next_index] = (byte)(arr2[str2_index] + arr2[str2_next_index]);

The function decrypt is a function to decrypt.
Pass the encrypted text and key as arguments.
The decrypted text is returned.

The rest is almost the same as when encrypting.

Example of use

Challenge the reader?

Even if you know the encryption algorithm this time, I don’t think you can guess the key and decrypt it.
I don’t know where that confidence comes from, but I think it’s very difficult because I’m constantly changing keys. (Do amateur feeling)
If you think you can do it, please decrypt the following encrypted version.

By the way, the key can also be used in Japanese.

135,168,181,167,173,90,27,45,183,0,220,38,143,140,145,252,201,93,82,34,227,101,95,234,150,153,76,118,94,33,1,93,20,74,41,192,184,27,143,147,163,76,95,170,199,9,222,177,50,45,233,232,244,49,173,221,229,158,220,65,132,217,75,38,221,150,20,152,149,2,64,172,236,151,155,98,78,22,237,202,107,47,40,205,107,160,67,237,166,173,235,46,249,188,154,9,241,140,222,211,209,101,136,149,175,224,113,128,100,233,145,140,153,104,201,230,10,165,140,115,161,124,85,76,206,185,67,158,7,201,153,124,44,29,200,170,132,29,145,4,228,15,230,139,19,78,71,91,193,93,225,154,