package gh;import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.Reader;
import java.util.HashMap;
import java.util.Iterator;
/*** 信息安全作业* @author ganhang**/
public class encrypt {private static HashMap<String, Integer> h=new HashMap<String, Integer>();public static void main(String[] args) {
//        System.out.println(readfile("2.txt"));
//        System.out.println(encode(readfile("2.txt"),3));
//        System.out.println(find(readfile("2.txt")));
        String encodeString =encode(readfile("2.txt"),3);//加密后的字符串String decodeString =decode(encodeString);//解密后的字符串
        System.out.println(decodeString);}/*** 解密* @param s*/public static String decode(String s){String maxString =find(s);//找出出现最多的字母//System.out.println(maxString);char maxchar='e';//自然状态下出现最多的字母char max =maxString.charAt(0);//转字母int shift=max-maxchar;//获得偏移量(这里是+3)return encode(s,0-shift);//(解密只需要偏移-3)
    }/*** 找出出现频率最高的字母* @param s* @return*/public static String find(String s){//HashMap<String, Integer> h=new HashMap<String, Integer>();char c[]=s.toCharArray();int count=0;for(int i=0;i<c.length;i++){if (c[i] <= 'Z' && c[i] >= 'A' || c[i] <= 'z' && c[i] >= 'a') {if(h.get(""+c[i])!=null)count=h.get(""+c[i]);h.put(c[i]+"",++count);}}int max=-1;String maxString=null;for (String str : h.keySet()) {if (h.get(str) > max) {max = h.get(str);maxString = str;}}return maxString;}/*** 读文件* @param url* @return*/public static String readfile(String url){StringBuilder sb = new StringBuilder();try {Reader in=new InputStreamReader(new FileInputStream(url));char []cbuf=new char[1024];int len;while((len=in.read(cbuf))!=-1){sb.append(cbuf);}in.close();} catch (FileNotFoundException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();}return sb.toString();}/*** 移位加密* @param s* @param key* @return*/public static String encode(String s, int key) {StringBuilder sb = new StringBuilder();char[] c = s.toCharArray();for (int i = 0; i < c.length; i++) {if (c[i] <= 'Z' && c[i] >= 'A' || c[i] <= 'z' && c[i] >= 'a') {char ch = (char) (c[i] + key);sb.append(ch);}elsesb.append(c[i]);}return sb.toString();}
}