C# Java间进行RSA加密解密交互 .

这里，讲一下RSA算法加解密在C#和Java之间交互的问题，这两天纠结了很久，也看了很多其他人写的文章，颇受裨益，但没能解决我的实际问题，终于，还是被我捣鼓出来了。

首先，介绍一下写这代码的目的：完成webService验证问题，服务器端采用C#开发，客户端采用Java开发。服务器端给客户端提供公钥，已进行数据加密，客户端加密后提数据提交给服务器，服务器用私钥对数据解密，进行验证。 

这里遇到的主要问题是C# RSACryptoServiceProvider类产生的公钥、私钥都是xml字符串数据，而java RSA算法要求的 Modulus、Exponent都是BigInteger类型，两者间的转换才是问题所在。 

关于Java 和 C#各自独立的进行RSA加密解密，大家可以看整两篇文章，java RSA加密解密实现（） 和 C#中RSA加密解密和签名与验证的实现。 

接下来讲一下实现步骤：

首先由C# RSACryptoServiceProvider类生成公钥、私钥

/// <summary>        /// 生成公钥、私钥        /// </summary>        /// <returns>公钥、私钥，公钥键"PUBLIC",私钥键"PRIVATE"</returns>        public Dictionary<string, string> createKeyPair()        {            Dictionary<string, string> keyPair = new Dictionary<string, string>();            RSACryptoServiceProvider provider = new RSACryptoServiceProvider(1024);            keyPair.Add("PUBLIC", provider.ToXmlString(false));            keyPair.Add("PRIVATE", provider.ToXmlString(true));            return keyPair;        }

如此处生成的公钥为

<RSAKeyValue><Modulus>t+56m5jXXonAJAKC7mgkhAZX5gWJTZojbSloLpLBGEWiebFaM+aUUKALfRx83/HaUV79ZiR3zuLJOLBdALx1cmcPk/b9fdNblLmzqi4cfSnfmMLWh05xf+ZS1pKHSKQtui3dfuu+3XH6Ak+S38dpIZUj/hihQQuKysN6GJ9h+c8=</Modulus><Exponent>AQAB</Exponent></RSAKeyValue>

在客户端(Java)对C#提供的公钥提取Modulus和Exponent

/** * 返回包含模数modulus和指数exponent的haspMap * @return * @throws MalformedURLException * @throws DocumentException */public static HashMap<String,String> rsaParameters(String xmlPublicKey) throws MalformedURLException, DocumentException{    HashMap<String ,String> map = new HashMap<String, String>(); Document doc = DocumentHelper.parseText(xmlPublicKey);String mudulus = (String) doc.getRootElement().element("Modulus").getData();String exponent = (String) doc.getRootElement().element("Exponent").getData();map.put("mudulus", mudulus);map.put("exponent", exponent);return map;}

用Modulus和Exponent产生公钥RSAPublicKey（java）

这里有个关键步骤先对Mudolus和Exponent进行Base64解码，这个是由于C#生成的密钥对，其参数已经过Base64编码成String类型，而java RSA参数是未经base64编码的byte[]类型。

至于Base64编码、解码方法，参考这篇文章，java 编码和解码，想详细。

public static byte[] decodeBase64(String input) throws Exception{          Class clazz=Class.forName("com.sun.org.apache.xerces.internal.impl.dv.util.Base64");          Method mainMethod= clazz.getMethod("decode", String.class);          mainMethod.setAccessible(true);           Object retObj=mainMethod.invoke(null, input);           return (byte[])retObj;      }/** * 返回RSA公钥 * @param modules * @param exponent * @return */public static PublicKey getPublicKey(String modulus, String exponent){try { byte[] m = decodeBase64(modulus);byte[] e = decodeBase64(exponent);            BigInteger b1 = new BigInteger(1,m);              BigInteger b2 = new BigInteger(1,e);              KeyFactory keyFactory = KeyFactory.getInstance("RSA");              RSAPublicKeySpec keySpec = new RSAPublicKeySpec(b1, b2);              return (RSAPublicKey) keyFactory.generatePublic(keySpec);          } catch (Exception e) {              e.printStackTrace();              return null;          }}

获得公钥后就可以进行RSA加密处理了，这里还有一点需要提的是，RSA加密解密都有最大长度限制，加密最大长度为117字节，解密最大长度是128字节，此外，此处加密得到的数据是经过Base64编码处理的

public static String encrypt(byte[] source, PublicKey publicKey) throws Exception{String encryptData ="";try {Cipher cipher = Cipher.getInstance("RSA");cipher.init(Cipher.ENCRYPT_MODE, publicKey);int length = source.length;int offset = 0;byte[] cache;ByteArrayOutputStream outStream = new ByteArrayOutputStream();int i = 0;while(length - offset > 0){if(length - offset > MAXENCRYPTSIZE){cache = cipher.doFinal(source, offset, MAXENCRYPTSIZE);}else{cache = cipher.doFinal(source, offset, length - offset);}outStream.write(cache, 0, cache.length);i++;offset = i * MAXENCRYPTSIZE;}return encodeBase64(outStream.toByteArray());} catch (NoSuchAlgorithmException e) {e.printStackTrace();} catch (NoSuchPaddingException e) {e.printStackTrace();} catch (InvalidKeyException e) {e.printStackTrace();} catch (IllegalBlockSizeException e) {e.printStackTrace();} catch (BadPaddingException e) {e.printStackTrace();}return encryptData;}

加密后的数据提交给C#服务器端进行解密，当然，这里也要注意最大长度限制问题

/// <summary>        /// RSA解密        /// </summary>        /// <param name="encryptData">经过Base64编码的密文</param>        /// <param name="privateKey">私钥</param>        /// <returns>RSA解密后的数据</returns>        public static string decrypt(string encryptData, string privateKey)        {            string decryptData = "";            try            {                RSACryptoServiceProvider provider = new RSACryptoServiceProvider();                provider.FromXmlString(privateKey);                byte[] bEncrypt = Convert.FromBase64String(encryptData);                                int length = bEncrypt.Length;                int offset = 0;                string cache ;                int i = 0;                while (length - offset > 0)                {                    if (length - offset > MAXDECRYPTSIZE)                    {                        cache = Encoding.UTF8.GetString(provider.Decrypt(getSplit(bEncrypt, offset, MAXDECRYPTSIZE), false));                    }                    else                    {                        cache = Encoding.UTF8.GetString(provider.Decrypt(getSplit(bEncrypt, offset, length - offset), false));                    }                    decryptData += cache;                    i++;                    offset = i*MAXDECRYPTSIZE;                }            }            catch(Exception e)            {                throw e;            }            return decryptData;        }        /// <summary>        /// 截取字节数组部分字节        /// </summary>        /// <param name="input"></param>        /// <param name="offset">起始偏移位</param>        /// <param name="length">截取长度</param>        /// <returns></returns>        private static byte[] getSplit(byte[] input, int offset, int length)        {             byte[] output = new byte[length];            for (int i = offset; i < offset + length; i++)            {                output[i - offset] = input[i];            }            return output;        }