online_security_project/lib/Utils.cs

using System.Linq;
using System.Text;

namespace lib;

public static class Utils
{
    public static byte[] NumberToBytes(string Number)
    {
        if (Number.Any(c => !char.IsDigit(c)) || Number.Length > 16)
        {
            throw new Exception("Invalid arguments!");
        }
        byte[] res = Enumerable.Repeat((byte)0b1111_1111, 8).ToArray();
        // Pad Number if needed to be of even length (because each 2 digits are turned into 1 byte)
        Number = Number.Length % 2 == 0 ? Number : Number + '-';

        for (int i = 0; i < Number.Length - 1; i += 2)
        {
            char c1 = Number[i];
            char c2 = Number[i + 1];
            res[i / 2] = (byte)((DigitToByte(c1) << 4) | DigitToByte(c2));
        }
        return res;
    }

    public static string BytesToNumber(byte[] Bytes)
    {
        string s = "";
        foreach (byte b in Bytes)
        {
            byte b1 = (byte)((b >> 4) & 0b1111);
            byte b2 = (byte)(b & 0b1111);
            s = s + ByteToDigit(b1) + ByteToDigit(b2);
        }
        return new string(s.Where(char.IsDigit).ToArray());
    }


    public static byte DigitToByte(char c)
    {
        if (int.TryParse(c.ToString(), out int d))
        {
            return (byte)d;
        }
        else
        {
            return 0b1111; // empty, turned into '-' later to be discarded
        }
    }

    public static char ByteToDigit(byte b)
    {
        byte offset = Encoding.ASCII.GetBytes("0")[0];

        if (b == 0b1111)
        {
            return '-';
        }
        else
        {
            return Encoding.ASCII.GetChars([(byte)(b + offset)])[0];
        }
    }
}