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 using System;
using System.Collections;
using System.IO;
using System.Security.Cryptography;
using System.Text;
using System.Web;

namespace Web
{
    public class RSA
    {
        int keySize;
        string publicKey;
        string privateKey;
        string publicKeyFileName;
        string privateKeyFileName;

        public RSA()
        {
            keySize = 1024;
            publicKeyFileName = "public.pk";
            privateKeyFileName = "private.pk";
            publicKey = ReadFile(publicKeyFileName);
            privateKey = ReadFile(privateKeyFileName);
            if (String.IsNullOrEmpty(publicKey) || String.IsNullOrEmpty(privateKey))
            {
                GenerateKey();
            }
        }

        private void GenerateKey()
        {
            RSACryptoServiceProvider RSA = new RSACryptoServiceProvider(keySize);

            publicKey = RSA.ToXmlString(true);
            privateKey = RSA.ToXmlString(false);

            if (SaveFile(privateKeyFileName, publicKey))
            {
                SaveFile(publicKeyFileName, privateKey);
            }
        }

        public string EncryptString(string text)
        {
            RSACryptoServiceProvider RSA = new RSACryptoServiceProvider(keySize);
            RSA.FromXmlString(publicKey);
            byte[] bytes = Encoding.UTF32.GetBytes(text);
            int maxLength = (keySize / 8) - 42;
            int dataLength = bytes.Length;
            int iterations = dataLength / maxLength;
            StringBuilder stringBuilder = new StringBuilder();
            for (int i = 0; i <= iterations; i++)
            {
                byte[] tempBytes = new byte[(dataLength - maxLength * i > maxLength) ? maxLength : dataLength - maxLength * i];
                Buffer.BlockCopy(bytes, maxLength * i, tempBytes, 0, tempBytes.Length);
                byte[] encryptedBytes = RSA.Encrypt(tempBytes, true);
                Array.Reverse(encryptedBytes);
                stringBuilder.Append(Convert.ToBase64String(encryptedBytes));
            }
            return stringBuilder.ToString();
        }

        public string DecryptString(string text)
        {
            RSACryptoServiceProvider RSA = new RSACryptoServiceProvider(keySize);
            RSA.FromXmlString(privateKey);
            int base64BlockSize = ((keySize / 8) % 3 != 0) ? (((keySize / 8) / 3) * 4) + 4 : ((keySize / 8) / 3) * 4;
            int iterations = text.Length / base64BlockSize;
            ArrayList arrayList = new ArrayList();
            for (int i = 0; i < iterations; i++)
            {
                byte[] encryptedBytes = Convert.FromBase64String(text.Substring(base64BlockSize * i, base64BlockSize));
                Array.Reverse(encryptedBytes);
                arrayList.AddRange(RSA.Decrypt(encryptedBytes, true));
            }
            return Encoding.UTF32.GetString(arrayList.ToArray(Type.GetType("System.Byte")) as byte[]);
        }

        private bool SaveFile(string fileName, string text)
        {
            try
            {
                string path = HttpContext.Current.Server.MapPath("/" + fileName);
                StreamWriter streamWriter = new StreamWriter(path, false);
                if (text != null) streamWriter.Write(text);
                streamWriter.Close();
                return true;
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }

        private string ReadFile(string fileName)
        {
            string text = null;
            string path = HttpContext.Current.Server.MapPath("/" + fileName);
            if (File.Exists(path))
            {
                StreamReader streamReader = new StreamReader(path, true);
                text = streamReader.ReadToEnd();
                streamReader.Close();
            }
            return text;
        }
    }
}