char[] asciiChars = new char[Encoding.GetEncoding(input_charset).GetCharCount(source, 0, source.Length)];

            Encoding.GetEncoding(input_charset).GetChars(source, 0, source.Length, asciiChars, 0);

            return new string(asciiChars);

        }

        private static byte[] decrypt(byte[] data, string privateKey, string input_charset)

        {

            RSACryptoServiceProvider rsa = DecodePemPrivateKey(privateKey);

            SHA1 sh = new SHA1CryptoServiceProvider();

            return rsa.Decrypt(data, false);

        }

        /// <summary>

        /// 解析java生成的pem文件私钥

        /// </summary>

        /// <param name="pemstr"></param>

        /// <returns></returns>

        private static RSACryptoServiceProvider DecodePemPrivateKey(String pemstr)

        {

            byte[] pkcs8privatekey;

            pkcs8privatekey = Convert.FromBase64String(pemstr);

            if (pkcs8privatekey != null)

            {

                RSACryptoServiceProvider rsa = DecodePrivateKeyInfo(pkcs8privatekey);

                return rsa;

            }

            else

                return null;

        }

        private static RSACryptoServiceProvider DecodePrivateKeyInfo(byte[] pkcs8)

        {

            byte[] SeqOID = { 0x30, 0x0D, 0x06, 0x09, 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x01, 0x05, 0x00 };

            byte[] seq = new byte[15];

            MemoryStream mem = new MemoryStream(pkcs8);

            int lenstream = (int)mem.Length;