C# RSA PEM解密字符

1、第一步先用openssl将pem的key转换为der的key //bin>openssl.exe rsa -in rsakeydec.pem -outform der -out pri.der 
2、调用下面的程序直接读取der转换为c#所需要的xml Key，之后进行密文解密

using System;

using System.IO;

using System.Security.Cryptography;

using System.Text;

namespace ConsoleApplication3 {

    class Program {

        private static int GetIntegerSize(BinaryReader binr) {

            int count;

            var bt = binr.ReadByte();

            if(bt != 0x02)        //expect integer

                return ;

            bt = binr.ReadByte();

            if(bt == 0x81)

                count = binr.ReadByte();    // data size in next byte

            else

                if(bt == 0x82) {

                var highbyte = binr.ReadByte();

                var lowbyte = binr.ReadByte();

                byte[] modint = { lowbyte,highbyte,0x00,0x00 };

                count = BitConverter.ToInt32(modint,);

            } else {

                count = bt;        // we already have the data size

            }

            while(binr.ReadByte() == 0x00) {    //remove high order zeros in data

                count -= ;

            }

            binr.BaseStream.Seek(-,SeekOrigin.Current);        //last ReadByte wasn't a removed zero, so back up a byte

            return count;

        }

        /// <summary>

        /// e.g:"D:\\pri.der";

        /// </summary>

        /// <param name="filePath"></param>

        /// <returns></returns>

        public static RSACryptoServiceProvider DecodeRsaPrivateKey(string filePath) {

            byte[] MODULUS, E, D, P, Q, DP, DQ, IQ;

            FileStream fs = new FileStream(filePath,FileMode.Open,FileAccess.Read);

            BinaryReader binr = new BinaryReader(fs);    //wrap Memory Stream with BinaryReader for easy reading

            try {

                var 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;

                var bt = binr.ReadByte();

                if(bt != 0x00)

                    return null;

                var 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 -----

                RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();

                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(Exception e) {

                Console.WriteLine(e.Message + e.StackTrace);

                return null;

            } finally {

                binr.Close();

            }

        }

        /// <summary>

        /// 导出私钥XML解密格式

        /// </summary>

        /// <returns></returns>

        public static string  PrivateKeyDecXml() {

            RSACryptoServiceProvider rsaProvider = DecodeRsaPrivateKey(@"D:\\pri.der");

            var privateKey = rsaProvider.ToXmlString(true);

            return privateKey;

        }

        /// <summary>

        /// RSA解密

        /// </summary>

        /// <param name="privatekey"></param>

        /// <param name="content"></param>

        /// <returns></returns>

        public static string RsaDecrypt(string privatekey,string content) {

            RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();

            byte[] cipherbytes;

            rsa.FromXmlString(privatekey);

            cipherbytes = rsa.Decrypt(Convert.FromBase64String(content),false);

            return Encoding.UTF8.GetString(cipherbytes);

        }

        static void Main(string[] args) {

        var str= PrivateKeyDecXml();

            var s = RsaDecrypt(str,

                "jB6EKo9Oakc8MYMlKorZmj415+s8Qf1sHr1MIPjZcybaFhRQDVb+MBZ734p45lc2RlEJUDsy5HRH8I4LvcGSNE0kJu+ge2yy9E8xOD3dWUTU9/30vv7cEbQ5WSHtjl0MyvhTX51x3vrW/oqubH0H3p827GF3c+ALPlxrvG1gHTc=");

        }

    }

}