程序猿成长之路之密码学篇-DES算法详解

DES的算法实现原理详情请见
https://blog.csdn.net/qq_31236027/article/details/128209185
DES算法密钥获取详情请见
https://blog.csdn.net/qq_31236027/article/details/129224730
编码工具类获取详见
https://blog.csdn.net/qq_31236027/article/details/128579451

DES算法实现思路：

1. 进行编码工具类的设计，主要设计以下几个方法：
   1. 字符串转二进制，用于明文加密
   2. 二进制转字符串，用于对解密二进制流与文本的转换
   3. 二进制转十六进制字符串，用于对加密后的文本进行传输和保存，防止出现乱码
   4. 十六进制转二进制，用于对加密后的文本进行解密
   5. 其他有需要的方法（如s盒的二进制转十进制)
2. 进行密钥获取工具类的设计
3. 进行des算法工具类的设计

密钥获取工具类的设计：

1. 设计一个初始化方法和两个数组，用于密钥第一次选择置换和接收左右半部分的32位二进制结果。
2. 初始化后进行16轮密钥的获取，最好能够存储在一个私有全局变量里，然后通过一个接口方法对外发布。（我这步没有做）

DES算法工具类的设计：

注意点：

1. 将获取的16轮密钥保存在一个全局变量，解密需要使用（只需要逆置即可)
2. 注意分组问题
3. ！！很重要的一点！！在加密后要将所有的十六进制流小写，大写的话会解密出现乱码。

最后上DES算法工具类实现代码：

package des;import java.io.UnsupportedEncodingException;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;import common.EncodeUtil;
import common.IEncrytion;
import common.EncodeUtil.EncodeRadix;/*** des加解密工具类* @author zygswo**/
public class DesUtil implements IEncrytion{/*** 加密轮数*/public static final int ROUND_NB = 16;/*** 字符串长度*/public static final int CHAR_LEN = 16;/*** 分组长度*/public static final int DIV_LEN = 64 / CHAR_LEN;/*** 密钥对象*/private KeyUtil subKeyObj = new KeyUtil().init(); public List<String> subKeys = Collections.synchronizedList(new ArrayList<>());/*** 初始置换PC表*/private static int[][] transferTable = {{58,50,42,34,26,18,10,2},{60,52,44,36,28,20,12,4},{62,54,46,38,30,22,14,6},{64,56,48,40,32,24,16,8},{57,49,41,33,25,17,9,1},{59,51,43,35,27,19,11,3},{61,53,45,37,29,21,13,5},{63,55,47,39,31,23,15,7}};/*** 扩展置换PC表*/private static int[][] transferExtendTable = {{32,1,2,3,4,5},{4,5,6,7,8,9},{8,9,10,11,12,13},{12,13,14,15,16,17},{16,17,18,19,20,21},{20,21,22,23,24,25},{24,25,26,27,28,29},{28,29,30,31,32,1}};/*** p盒置换表*/private static int[][] pTransferTable = {{16,7,20,21},{29,12,28,17},{1,15,23,26},{5,18,31,10},{2,8,24,14},{32,27,3,9},{19,13,30,6},{22,11,4,25}};/*** 逆初始置换PC-1表*/private static int[][] transferReverseTable = {{40,8,48,16,56,24,64,32},{39,7,47,15,55,23,63,31},{38,6,46,14,54,22,62,30},{37,5,45,13,53,21,61,29},{36,4,44,12,52,20,60,28},{35,3,43,11,51,19,59,27},  {34,2,42,10,50,18,58,26},{33,1,41,9,49,17,57,25}};/*** s盒置换表*/private static int[][][] sBox = {{{14,4,13,1,2,15,11,8,3,10,6,12,5,9,0,7},{0,15,7,4,14,2,13,1,10,6,12,11,9,5,3,8},{4,1,14,8,13,6,2,11,15,12,9,7,3,10,5,0},{15,12,8,2,4,9,1,7,5,11,3,14,10,0,6,13}},{{15,1,8,14,6,11,3,4,9,7,2,13,12,0,5,10},{3,13,4,7,15,2,8,14,12,0,1,10,6,9,11,5},{0,14,7,11,10,4,13,1,5,8,12,6,9,3,2,15},{13,8,10,1,3,15,4,2,11,6,7,12,0,5,14,9}},{{10,0,9,14,6,3,15,5,1,13,12,7,11,4,2,8},{13,7,0,9,3,4,6,10,2,8,5,14,12,11,15,1},{13,6,4,9,8,15,3,0,11,1,2,12,5,10,14,7},{1,10,13,0,6,9,8,7,4,15,14,3,11,5,2,12}},{{7,13,14,3,0,6,9,10,1,2,8,5,11,12,4,15},{13,8,11,5,6,15,0,3,4,7,2,12,1,10,14,9},{10,6,9,0,12,11,7,13,15,1,3,14,5,2,8,4},{3,15,0,6,10,1,13,8,9,4,5,11,12,7,2,14}},{{2,12,4,1,7,10,11,6,8,5,3,15,13,0,14,9},{14,11,2,12,4,7,13,1,5,0,15,10,3,9,8,6},{4,2,1,11,10,13,7,8,15,9,12,5,6,3,0,14},{11,8,12,7,1,14,2,13,6,15,0,9,10,4,5,3}},{{12,1,10,15,9,2,6,8,0,13,3,4,14,7,5,11},{10,15,4,2,7,12,9,5,6,1,13,14,0,11,3,8},{9,14,15,5,2,8,12,3,7,0,4,10,1,13,11,6},{4,3,2,12,9,5,15,10,11,14,1,7,6,0,8,13}},{{4,11,2,14,15,0,8,13,3,12,9,7,5,10,6,1},{13,0,11,7,4,9,1,10,14,3,5,12,2,15,8,6},{1,4,11,13,12,3,7,14,10,15,6,8,0,5,9,2},{6,11,13,8,1,4,10,7,9,5,0,15,14,2,3,12}},{{13,2,8,4,6,15,11,1,10,9,3,14,5,0,12,7},{1,15,13,8,10,3,7,4,12,5,6,11,0,14,9,2},{7,11,4,1,9,12,14,2,0,6,10,13,15,3,5,8},{2,1,14,7,4,10,8,13,15,12,9,0,3,5,6,11}}};/*** 解密* @param encrytedText 密文* @return 明文*/@Overridepublic String decrypt(String encrytedText) {StringBuilder sb = new StringBuilder();// CHAR_LEN = divLeng * 4 (16进制4位，转16位需要4个16进制位）int divLeng = 16;int length = encrytedText.length()% divLeng == 0 ? encrytedText.length()/divLeng : (encrytedText.length()/divLeng + 1);for (int i = 0; i<length; i++) {int startIndex = i * divLeng;int endIndex = (startIndex + divLeng) > encrytedText.length() ? encrytedText.length() : (startIndex + divLeng);String str1 = encrytedText.substring(startIndex, endIndex);sb.append(baseDecrypt(EncodeUtil.toBinary(str1,EncodeRadix.HEX)));}return sb.toString().trim();}/*** 解密(64位一组)* @param encrytedText 密文* @return*/private String baseDecrypt(String encrytedText) {//1.初始置换//获取16组密钥List<String> reversedSubkeys = new ArrayList<>();for (int i = subKeys.size() -1; i >=0 ;i--) {reversedSubkeys.add(subKeys.get(i));}//16次循环加密return EncodeUtil.binaryToStr(loops(encrytedText, reversedSubkeys,false),CHAR_LEN).trim();}/*** 分组加密* @param text 明文* @return 密文*/@Overridepublic String encrypt(String text) {StringBuilder sb = new StringBuilder();// DIV_LEN * CHAR_LEN = 64 // 根据DIV_LEN进行分组，如CHAR_LEN=16位，那么就每4个字符一组int length = text.length()% DIV_LEN == 0 ? text.length()/DIV_LEN : (text.length()/DIV_LEN + 1);for (int i = 0; i<length; i++) {int startIndex = i * DIV_LEN;int endIndex = (startIndex + DIV_LEN) > text.length() ? text.length() : (startIndex + DIV_LEN);String str1 = text.substring(startIndex, endIndex);//尾部填充while (str1.length() < DIV_LEN) {str1 += " ";}sb.append(baseEncrypt(str1));}return sb.toString().toLowerCase().trim(); //注意，加密后一定要为小写,大写后会出错}/*** 加密（每个密文都是64位）* @param text* @return*/private String baseEncrypt(String text) {//获取16组密钥if (subKeys == null || subKeys.isEmpty()) {subKeys = subKeyObj.generateKey();}//16次循环加密return EncodeUtil.binaryToHexStr(loops(text, subKeys, true)).trim();}/*** 16轮循环加密* @param step1Result 初始置换后的结果* @param subKeys 16组子密钥* @param isEncrypt 是否加密* @return 循环加密结果*/private String loops(String text, List<String> subKeys, boolean isEncrypt) {//1.初始置换String str64bit = text;if (isEncrypt) {str64bit = EncodeUtil.strtoBinary(text,CHAR_LEN);}str64bit = swap(str64bit, transferTable);if (str64bit.length() != 64) {throw new IllegalArgumentException("初始置换后的结果不为64位");}if (subKeys.size() != 16) {throw new IllegalArgumentException("加密密钥组数不为16组");}//主体部分String leftPart = str64bit.substring(0,32); //高位String rightPart = str64bit.substring(32);  //低位for (String subKey: subKeys) {//右半边参与f函数运算String temp = rightPart;//获取f函数结果String fResult = fFunction(rightPart,subKey);//f函数结果与左半部分进行异或运算rightPart = xor(fResult, leftPart);//左右交换leftPart = temp;}//逆初始置换return swap(rightPart+leftPart, transferReverseTable);}/*** f函数* @param str32Bit 右半部分* @param subKey 子密钥* @return f函数结果*/private String fFunction(String str32Bit, String subKey) {//1. 扩展运算，将rightPart32位转成48位String str48Bit = swap(str32Bit, transferExtendTable);//2. 与密钥进行异或运算String result = xor(str48Bit, subKey);char[] res = result.toCharArray();//3. s盒运算String[] sBoxTmp = new String[8];StringBuilder sBoxResult = new StringBuilder();  //p盒运算用for(int i=0; i<sBoxTmp.length; i++) {//每6位为一组输入（首位和末尾位为行索引，中间四位为列索引）int rowNb = Integer.valueOf(EncodeUtil.binaryToDec(res[i*6] + "" + res[i*6 + 5]));int colNb = Integer.valueOf(EncodeUtil.binaryToDec(res[i*6 + 1] + "" + res[i*6 + 2]+ res[i*6 + 3]+ res[i*6 + 4]));sBoxTmp[i] = EncodeUtil.decToBinary(sBox[i][rowNb][colNb]+"",4);}for(String res1: sBoxTmp) {sBoxResult.append(res1);}//4. p盒置换运算return swap(sBoxResult.toString().trim(),pTransferTable);}/*** 异或运算* @param text1 text1 * @param text2 text2* @return*/private String xor(String text1, String text2) {if (text1 == null || text2 == null || text1.length() != text2.length()) {throw new IllegalArgumentException("异或运算失败");}StringBuilder sb = new StringBuilder();for (int i = 0; i < text1.length();i++) {char ch1 = text1.charAt(i);char ch2 = text2.charAt(i);sb.append((ch1) ^ (ch2));}return sb.toString().trim();}/*** 置换运算* @param text 文本* @param table 置换运算表* @return 置换运算后结果*/private String swap(String text,int[][] table) {char[] chs = text.toCharArray();StringBuilder sb = new StringBuilder();int rowNb = table.length;int colNb = table[0].length;for (int i = 0; i < rowNb * colNb;i++) {sb.append(chs[table[i/colNb][i%colNb] - 1]);}return sb.toString().trim();}public static void main(String[] args) throws NoSuchAlgorithmException, UnsupportedEncodingException {/*** desutil使用方法* 1. 使用base64编码字符串* 2. 使用des加密，获得16进制字符串*/DesUtil util = new DesUtil();String result = util.encrypt("{\"code\":200,\"message\":\"成功！\",\"data\":{\"id\": \"2103813902831\"}}");System.out.println("encrypt result=" + result);System.out.println("decrypt result = " + util.decrypt(result));}
}

存在的不足

1. 密钥较短（64位），安全性能较差，很容易被破解
2. 加密后文本较长
3. 处理速度较慢

后续改进方案

1. 缩短加密后文本长度
2. 尝试使用多线程处理，加快处理速度。
3. 尝试更长密钥的版本。