RAS 算法 私钥加密，公钥解密 Java 转 .net；

对接第三方接口，接口返回来的参数是经过 RAS 分段式 算法 加密后的，采用私钥加密，公钥解密，第三方提供公钥；

参考资料地址：

https://www.cnblogs.com/datous/p/RSAKeyConvert.html

https://www.bbsmax.com/A/RnJW6B4Ozq/

步骤：

①：先将java的公钥转成 .net 的公钥；一般来说 .net 的公钥是xml格式 （这里提供 公钥，私钥转换方法）

 /// <summary>
        /// RSA私钥格式转换，java->.net
        /// </summary>
        /// <param name="privateKey">java生成的RSA私钥</param>
        /// <returns></returns>
        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()));
        }
        /// <summary>
        /// RSA公钥格式转换，java->.net
        /// </summary>
        /// <param name="publicKey">java生成的公钥</param>
        /// <returns></returns>
        public static string RSAPublicKeyJava2DotNet(string publicKey)
        {
            RsaKeyParameters publicKeyParam = (RsaKeyParameters)PublicKeyFactory.CreateKey(Convert.FromBase64String(publicKey));
            return string.Format("<RSAKeyValue><Modulus>{0}</Modulus><Exponent>{1}</Exponent></RSAKeyValue>",
                Convert.ToBase64String(publicKeyParam.Modulus.ToByteArrayUnsigned()),
                Convert.ToBase64String(publicKeyParam.Exponent.ToByteArrayUnsigned()));
        }

　　

②：根据转换过后的公钥 解密加密的字符串 （因为 .net 和 .net core 不同；t ）

/// <summary>
        /// 用公钥给数据进行RSA解密 
        /// </summary>
        /// <param name="xmlPublicKey"> 公钥(XML格式字符串) </param>
        /// <param name="strDecryptString"> 要解密数据 </param>
        /// <returns> 解密后的数据 </returns>
        public static string PublicKeyDecrypt(string strDecryptString)
        {
            var xmlPublicKey = RSAPublicKeyJava2DotNet(publicKey);
            #region .net 时使用
            //加载公钥
            // RSACryptoServiceProvider publicRsa = new RSACryptoServiceProvider();
            //publicRsa.FromXmlString(xmlPublicKey);
            #endregion

            #region .net core 使用 需要 通过 FromXmlString 方法转换类型
            var publicRsa = RSA.Create();
            publicRsa.ImportParameters(FromXmlString(xmlPublicKey));
            #endregion

            RSAParameters rp = publicRsa.ExportParameters(false);
            //转换密钥
            AsymmetricKeyParameter pbk = DotNetUtilities.GetRsaPublicKey(rp);

            IBufferedCipher c = CipherUtilities.GetCipher("RSA/ECB/PKCS1Padding");
            //第一个参数为true表示加密，为false表示解密；第二个参数表示密钥
            c.Init(false, pbk);
            byte[] outBytes = null;
            byte[] dataToDecrypt = Convert.FromBase64String(strDecryptString);
            #region 分段解密
            int keySize = publicRsa.KeySize / 8;
            byte[] buffer = new byte[keySize];

            using (MemoryStream input = new MemoryStream(dataToDecrypt))
            using (MemoryStream output = new MemoryStream())
            {
                while (true)
                {
                    int readLine = input.Read(buffer, 0, keySize);
                    if (readLine <= 0)
                    {
                        break;
                    }
                    byte[] temp = new byte[readLine];
                    Array.Copy(buffer, 0, temp, 0, readLine);
                    byte[] decrypt = c.DoFinal(temp);
                    output.Write(decrypt, 0, decrypt.Length);
                }
                outBytes = output.ToArray();
            }
            #endregion
            //byte[] outBytes = c.DoFinal(DataToDecrypt);//解密

            string strDec = Encoding.UTF8.GetString(outBytes);
            return strDec;
        }
        public static  RSAParameters FromXmlString(string xmlString)
        {
            RSAParameters parameters = new RSAParameters();

            XmlDocument xmlDoc = new XmlDocument();
            xmlDoc.LoadXml(xmlString);

            if (xmlDoc.DocumentElement.Name.Equals("RSAKeyValue"))
            {
                foreach (XmlNode node in xmlDoc.DocumentElement.ChildNodes)
                {
                    switch (node.Name)
                    {
                        case "Modulus": parameters.Modulus = (string.IsNullOrEmpty(node.InnerText) ? null : Convert.FromBase64String(node.InnerText)); break;
                        case "Exponent": parameters.Exponent = (string.IsNullOrEmpty(node.InnerText) ? null : Convert.FromBase64String(node.InnerText)); break;
                        case "P": parameters.P = (string.IsNullOrEmpty(node.InnerText) ? null : Convert.FromBase64String(node.InnerText)); break;
                        case "Q": parameters.Q = (string.IsNullOrEmpty(node.InnerText) ? null : Convert.FromBase64String(node.InnerText)); break;
                        case "DP": parameters.DP = (string.IsNullOrEmpty(node.InnerText) ? null : Convert.FromBase64String(node.InnerText)); break;
                        case "DQ": parameters.DQ = (string.IsNullOrEmpty(node.InnerText) ? null : Convert.FromBase64String(node.InnerText)); break;
                        case "InverseQ": parameters.InverseQ = (string.IsNullOrEmpty(node.InnerText) ? null : Convert.FromBase64String(node.InnerText)); break;
                        case "D": parameters.D = (string.IsNullOrEmpty(node.InnerText) ? null : Convert.FromBase64String(node.InnerText)); break;
                    }
                }
            }
            else
            {
                throw new Exception("Invalid XML RSA key.");
            }

            // rsa.ImportParameters(parameters);
            return parameters;
        }