理论可以参考百度；关于加密解密过程降解，觉得比较好的：一篇博文

因客户要求把web页面提交/验证改用RSA算法加密密文传递到后台：

1，js/jsp客户端部分RSA加密密码；

2，服务端Java解密；

基本流程：

a：以RSA算法在服务端生成密钥对（PublicKey,PrivateKey）,session中保存私钥；

b：把公钥Base64编码为Base64字符串通过http response传递到前台；

c：客户端（js）读取公钥解码，以公钥为参数RSA算法加密‘用户密码’，编码为Base64String，提交至服务端；

d：服务端Base64转码‘用户密码’字符串，并以RSA算法(私钥为参数)解密

e：比较验证解密后的字符串密码；

实现的基本库：

1，客户端js库jsencrypt-2.1.0

2，服务端采用JDK API（java.security.*,javax.crypto.*）,apache的commons-codec-1.9

实现细节问题：

1，jsencrypt只用到了加密过程，并且长度不能超过117个英文字符；

2，jdk解密时，密文超过128会出BadPaddingException异常；

3，所以在客户端大于117字符时按117长度分段加密，并按特定分隔符连接提交，在服务端分割字符串后分段解密还原；

代码：

（部分，不含Servlet）

客户端:

   var enc = function(){var pubkeystr = "MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDekiyV+vuvwcqGG2gvVCy/YbL94ke3kWK2ffgiA9puLshrooaHUHVVSyKjnb2qO47ZFEAL41gTt5jY05+r1w/DdLLLjsN8N7rIwNHDmZ2UaitRR5Vo1d+aI4edS+58pUmzUvhQwxpIJSo7JqZtSAtx6OELSwlSUjC+fRX0wiWjHQIDAQAB";var crypt = new JSEncrypt();crypt.setKey(pubkeystr);var datastr = $("#data").val();var result = "";for(var i=0; i<datastr.length; i+=117){            //  应当： substring(i,i+117) //如果i+117< length;//  应当： substring(i,length)//如果i+117>lengthvar sub = datastr.substring(i,i+117);if (""===result){result = crypt.encrypt(sub);}else{result += ","+crypt.encrypt(sub);}              }return result;}

服务端：

 public static void createkeypair(){try {SecureRandom sr = new SecureRandom();KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");kpg.initialize(1024, sr);KeyPair kp = kpg.genKeyPair();System.out.println("Generate KeyPair:");PrivateKey pvk = kp.getPrivate();String pvkb64 = Base64.encodeBase64String(pvk.getEncoded());System.out.println("PrivateKey(Base64String):\r\n"+pvkb64);PublicKey pbk = kp.getPublic();String pbk64 = Base64.encodeBase64String(pbk.getEncoded());System.out.println("PublicKey(Base64String):\r\n"+pbk64); } catch (NoSuchAlgorithmException e) {System.err.println(e.toString());}}public static byte[] decspec(byte[] keyv, byte[] encdata) throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeySpecException, InvalidKeyException, IllegalBlockSizeException, BadPaddingException{PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyv); //编码标准 //PKCS8解密 配合 X509加密      PrivateKey pvk = KeyFactory.getInstance("RSA").generatePrivate(pkcs8KeySpec);Cipher ce = Cipher.getInstance(pvk.getAlgorithm());ce.init(Cipher.DECRYPT_MODE, pvk);return ce.doFinal(encdata);}public static void decBase64Array(){//分段得到，OKString encodedata3 = "rOMx3LB0+n5J2OJBzZN8p2U+Q2uIlMvQbeSTnWqzU1tcUYreYh4fXEwSIAwgfsCMLCnmRLD0Rh3qx3+4d3lHZAo/eWKtSgjOH2fqxtzvnlDMiKVpU0OHCd441EUnlfDCJyKC5z5iC6uNOiGbzKNtmhpvz+18wbCuDV9CoCI49Pk=,OpFfPpYm2rbJYzflRg8hiRY+PSUcGECFTs7nq9bVgkeLBi+e7yU3reOkLCMr/WK9LvGNFAhQl+pZftSeh+4XZQGIcOZVgHarFS7GYdhy9xnEq3cocRR1mnIHlq7NVLR18QJYsE+pCs/oi1rRpNXw5KG6C2cywDl8/JuqsWnYRaw=,FbGedocEygHd/+MTztmHJrPb4nSW4wrJ29piSvvmKoajZRJbWukWIulqlzSQ87Vxem0OPYa3cIsVLOGZkhq5qnfkG7EDm9LijFLVTUbnZ9T3pfQOaSXC9gUjAi5ut9AzGVwKEmImIOQjOeHBvYpUkgn6G/J8YLH6L0obd9lFTMQ=";String privatekstr = "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";String[] arrs = encodedata3.split("\\,");for (int i = 0; i < arrs.length; i++) {byte[] data = Base64.decodeBase64(arrs[i]);//解码，得到RSA加密的数据byte[] pvencoded = Base64.decodeBase64(privatekstr);//解码，得到私钥数据          try {                           byte[] databytes = decspec(pvencoded,data);//解密                System.out.println("Recovered data:\r\n" + new String(databytes,"utf-8"));} catch (Exception e) {System.err.println(e.toString());} }}