using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;
 
namespace Common
{
    public class RSA
    {
        /// <summary>
        /// RSA公钥加密
        /// </summary>
        /// <param name="publickey">公钥</param>
        /// <param name="content">待加密字符串</param>
        /// <param name="input_charset">编码格式，UTF-8</param>
        /// <returns></returns>
        public static string RasEncrypt(string publickey, string content, string input_charset)
        {
            RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
            byte[] cipherbytes;
            rsa.ImportParameters(ConvertFromPublicKey(publickey));
            cipherbytes = rsa.Encrypt(Encoding.GetEncoding(input_charset).GetBytes(content), false);
            return Convert.ToBase64String(cipherbytes);
        }
 
        /// <summary>
        /// RSA私钥解密
        /// </summary>
        /// <param name="resData">RSA加密后字符串</param>
        /// <param name="privateKey">私钥</param>
        /// <param name="input_charset">编码格式，UTF-8</param>
        /// <returns>明文</returns>
        public static string RsaDecrypt(string resData, string privateKey, string input_charset)
        {
            byte[] DataToDecrypt = Convert.FromBase64String(resData);
            string result = "";
            for (int j = 0; j < DataToDecrypt.Length / 128; j++)
            {
                byte[] buf = new byte[128];
                for (int i = 0; i < 128; i++)
                {
 
                    buf[i] = DataToDecrypt[i + 128 * j];
                }
                result += decrypt(buf, privateKey, input_charset);
            }
            return result;
        }
 
        #region 内部方法
 
        private static string decrypt(byte[] data, string privateKey, string input_charset)
        {
            string result = "";
            RSACryptoServiceProvider rsa = DecodePemPrivateKey(privateKey);
            using (var sh = SHA1.Create())
            {
                byte[] source = rsa.Decrypt(data, false);
                char[] asciiChars = new char[Encoding.GetEncoding(input_charset).GetCharCount(source, 0, source.Length)];
                Encoding.GetEncoding(input_charset).GetChars(source, 0, source.Length, asciiChars, 0);
                result = new string(asciiChars);
                return result;
            }
 
        }
 
        private static RSACryptoServiceProvider DecodePemPrivateKey(String pemstr)
        {
            RSACryptoServiceProvider rsa = DecodeRSAPrivateKey(Convert.FromBase64String(pemstr));
            return rsa;
        }
 
        private static RSACryptoServiceProvider DecodeRSAPrivateKey(byte[] privkey)
        {
            byte[] MODULUS, E, D, P, Q, DP, DQ, IQ;
 
            // --------- Set up stream to decode the asn.1 encoded RSA private key ------
            MemoryStream mem = new MemoryStream(privkey);
            BinaryReader binr = new BinaryReader(mem); //wrap Memory Stream with BinaryReader for easy reading
            byte bt = 0;
            ushort twobytes = 0;
            int elems = 0;
            try
            {
                twobytes = binr.ReadUInt16();
                if (twobytes == 0x8130) //data read as little endian order (actual data order for Sequence is 30 81)
                    binr.ReadByte(); //advance 1 byte
                else if (twobytes == 0x8230)
                    binr.ReadInt16(); //advance 2 bytes
                else
                    return null;
 
                twobytes = binr.ReadUInt16();
                if (twobytes != 0x0102) //version number
                    return null;
                bt = binr.ReadByte();
                if (bt != 0x00)
                    return null;
 
 
                //------ all private key components are Integer sequences ----
                elems = GetIntegerSize(binr);
                MODULUS = binr.ReadBytes(elems);
 
                elems = GetIntegerSize(binr);
                E = binr.ReadBytes(elems);
 
                elems = GetIntegerSize(binr);
                D = binr.ReadBytes(elems);
 
                elems = GetIntegerSize(binr);
                P = binr.ReadBytes(elems);
 
                elems = GetIntegerSize(binr);
                Q = binr.ReadBytes(elems);
 
                elems = GetIntegerSize(binr);
                DP = binr.ReadBytes(elems);
 
                elems = GetIntegerSize(binr);
                DQ = binr.ReadBytes(elems);
 
                elems = GetIntegerSize(binr);
                IQ = binr.ReadBytes(elems);
 
 
                // ------- create RSACryptoServiceProvider instance and initialize with public key -----
                CspParameters CspParameters = new CspParameters();
                CspParameters.Flags = CspProviderFlags.UseMachineKeyStore;
                RSACryptoServiceProvider RSA = new RSACryptoServiceProvider(1024, CspParameters);
                RSAParameters RSAparams = new RSAParameters();
                RSAparams.Modulus = MODULUS;
                RSAparams.Exponent = E;
                RSAparams.D = D;
                RSAparams.P = P;
                RSAparams.Q = Q;
                RSAparams.DP = DP;
                RSAparams.DQ = DQ;
                RSAparams.InverseQ = IQ;
                RSA.ImportParameters(RSAparams);
                return RSA;
            }
            catch
            {
                return null;
            }
            finally
            {
                binr.Dispose();
            }
        }
 
        private static int GetIntegerSize(BinaryReader binr)
        {
            byte bt = 0;
            byte lowbyte = 0x00;
            byte highbyte = 0x00;
            int count = 0;
            bt = binr.ReadByte();
            if (bt != 0x02) //expect integer
                return 0;
            bt = binr.ReadByte();
 
            if (bt == 0x81)
                count = binr.ReadByte(); // data size in next byte
            else
                if (bt == 0x82)
            {
                highbyte = binr.ReadByte(); // data size in next 2 bytes
                lowbyte = binr.ReadByte();
                byte[] modint = { lowbyte, highbyte, 0x00, 0x00 };
                count = BitConverter.ToInt32(modint, 0);
            }
            else
            {
                count = bt; // we already have the data size
            }
 
            while (binr.ReadByte() == 0x00)
            { //remove high order zeros in data
                count -= 1;
            }
            binr.BaseStream.Seek(-1, SeekOrigin.Current); //last ReadByte wasn't a removed zero, so back up a byte
            return count;
        }
 
        #endregion
 
        #region 生成的Pem
        private static RSAParameters ConvertFromPublicKey(string pemFileConent)
        {
 
            if (string.IsNullOrEmpty(pemFileConent))
            {
                throw new ArgumentNullException("pemFileConent", "This arg cann't be empty.");
            }
            pemFileConent = pemFileConent.Replace("-----BEGIN PUBLIC KEY-----", "").Replace("-----END PUBLIC KEY-----", "").Replace("\n", "").Replace("\r", "");
            byte[] keyData = Convert.FromBase64String(pemFileConent);
            bool keySize1024 = (keyData.Length == 162);
            bool keySize2048 = (keyData.Length == 294);
            if (!(keySize1024 || keySize2048))
            {
                throw new ArgumentException("pem file content is incorrect, Only support the key size is 1024 or 2048");
            }
            byte[] pemModulus = (keySize1024 ? new byte[128] : new byte[256]);
            byte[] pemPublicExponent = new byte[3];
            Array.Copy(keyData, (keySize1024 ? 29 : 33), pemModulus, 0, (keySize1024 ? 128 : 256));
            Array.Copy(keyData, (keySize1024 ? 159 : 291), pemPublicExponent, 0, 3);
            RSAParameters para = new RSAParameters();
            para.Modulus = pemModulus;
            para.Exponent = pemPublicExponent;
            return para;
        }
 
        #endregion
 
    }
}