RSA加密方法

/// <summary>
        /// rsa加密
        /// </summary>
        /// <param name="data"></param>
        /// <param name="privatekey"></param>
        /// <returns></returns>

        public static string rsasigncharset(string data, string privatekey)
        {

            byte[] signaturebytes = null;

            rsacryptoserviceprovider rsacsp = loadcertificatestring(privatekey, "");

            byte[] databytes = encoding.utf8.getbytes(data);

            signaturebytes = rsacsp.signdata(databytes, "sha256");
            return convert.tobase64string(signaturebytes);
        }

        private static rsacryptoserviceprovider loadcertificatestring(string strkey, string signtype)
        {
            byte[] data = null;
            //读取带
            //ata = encoding.default.getbytes(strkey);
            data = convert.frombase64string(strkey);
            //data = getpem("rsa private key", data);
            try
            {
                rsacryptoserviceprovider rsa = decodersaprivatekey(data, signtype);
                return rsa;
            }
            catch (exception ex)
            {
                //    throw new aopexception("encryptcontent = woshihaoren,zheshiyigeceshi,wanerde", ex);
            }
            return null;
        }

        private static rsacryptoserviceprovider decodersaprivatekey(byte[] privkey, string signtype)
        {
            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;

                int bitlen = 1024;
                if ("rsa2".equals(signtype))
                {
                    bitlen = 2048;
                }

                rsacryptoserviceprovider rsa = new rsacryptoserviceprovider(bitlen, 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 (exception ex)
            {
                return null;
            }
            finally
            {
                binr.close();
            }
        }

        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;
        }