public static string RSAPrivateKeyJava2DotNet(string privateKey)

{

            RsaPrivateCrtKeyParameters privateKeyParam = (RsaPrivateCrtKeyParameters)PrivateKeyFactory.CreateKey(Convert.FromBase64String(privateKey));

            return string.Format("<RSAKeyValue><Modulus>{0}</Modulus><Exponent>{1}</Exponent><P>{2}</P><Q>{3}</Q><DP>{4}</DP><DQ>{5}</DQ><InverseQ>{6}</InverseQ><D>{7}</D></RSAKeyValue>",

                Convert.ToBase64String(privateKeyParam.Modulus.ToByteArrayUnsigned()),

                Convert.ToBase64String(privateKeyParam.PublicExponent.ToByteArrayUnsigned()),

                Convert.ToBase64String(privateKeyParam.P.ToByteArrayUnsigned()),

                Convert.ToBase64String(privateKeyParam.Q.ToByteArrayUnsigned()),

                Convert.ToBase64String(privateKeyParam.DP.ToByteArrayUnsigned()),

                Convert.ToBase64String(privateKeyParam.DQ.ToByteArrayUnsigned()),

                Convert.ToBase64String(privateKeyParam.QInv.ToByteArrayUnsigned()),

                Convert.ToBase64String(privateKeyParam.Exponent.ToByteArrayUnsigned()));

}

public static string Sign(string contentForSign, string privateKey)

        {

            //转换成适用于.Net的秘钥

            var netKey = RSAPrivateKeyJava2DotNet(privateKey);

            var rsa = new RSACryptoServiceProvider();

            rsa.FromXmlString(netKey);

            //创建一个空对象

            var rsaClear = new RSACryptoServiceProvider();

            var paras = rsa.ExportParameters(true);

            rsaClear.ImportParameters(paras);

            //签名返回

            using (var sha256 = new SHA256CryptoServiceProvider())

            {

                var signData = rsa.SignData(Encoding.UTF8.GetBytes(contentForSign), sha256);

                return BytesToHex(signData);

            }

        } 

public static string BytesToHex(byte[] data)

{

            StringBuilder sbRet = new StringBuilder(data.Length * 2);

            for (int i = 0; i < data.Length; i++)

            {

                sbRet.Append(Convert.ToString(data[i], 16).PadLeft(2, '0'));

            }

            return sbRet.ToString();

}

string rsaSecret = @"MIIBUwIBADANBgkqhkiG9w0BAQEFAASCAT0wggE5AgEAAkEAjdAhDuqzKCzaYyrrxFLdWVoR7wwmSdbVHBSZ/lpILvN/vPaohbi0NChwAEXYbvIXrFQ7zQyuqKazoEbvvXRNKQ.......";

string signDataString = Sign("Hello World!", rsaSecret);