写加密方法，希望大神知点和分享我们的技术

/**
* 将接收到的site_guide_id进行转码到页面显示
* @param num site_guide_id
* @return 转码后的字符串
*/
public static String encodeShowId(Long num){
System.out.println(" 加密的 === num : "+num);
int a = 510;
int b = 3;
String letter[] = { "A", "B", "C", "D", "E", "F", "G", "H", "I", "G"};
//随便进行运算后再将后两位远的成字母显示
int newnum= num.intValue()*a/b;
String pass = newnum  + (letter[newnum%100/10])+ (letter[newnum%10]);
return pass;
}
/**
* 将页面显示的转码后的GUIDE_ID反编码
* @param pass
* @return
*/
public static int decodeShowId(String pass){
int a = 510;
int b = 3;
//去掉后两位再按原规则反向运算
String left =  pass.substring(0,pass.length()-2);
int num = Integer.parseInt(left);
num = num*b/a;
return num;

}