一、密钥长度处理

实现了小于8 bytes的密钥都可以进行测试，原理其实很简单，只需要在密钥生成的时候对密钥的长度进行判断，不够的进行补0操作。

//密钥生成public StringBuffer[] getSubkey() {StringBuffer keyBinary = new StringBuffer(stringBufferToBinary(key)); //把密钥转成二进制StringBuffer subkey[] = new StringBuffer[16];  //subkey数组用来存储子密钥StringBuffer C0 = new StringBuffer(); //左密钥StringBuffer D0 = new StringBuffer(); //右密钥//判断密钥长度while (keyBinary.length() < 64) {keyBinary.append("0");}//PC1置换（64 bits --> 56 bits）for (int i = 0; i < 28; i++) {C0.append(keyBinary.charAt(PC1[i] - 1));D0.append(keyBinary.charAt(PC1[i + 28] - 1));}//16轮循环生成子密钥//16轮移位操作，每轮左移一位，特殊情况左移两位（查看密钥移位表）for (int i = 0; i < 16; i++) {//把第一位删了添加到最后一位char tmp;tmp = C0.charAt(0);C0.deleteCharAt(0);C0.append(tmp);tmp = D0.charAt(0);D0.deleteCharAt(0);D0.append(tmp);//特殊位置左移两位if (i != 0 && i != 1 && i != 8 && i != 15) {tmp = C0.charAt(0);C0.deleteCharAt(0);C0.append(tmp);tmp = D0.charAt(0);D0.deleteCharAt(0);D0.append(tmp);}//左右合并StringBuffer CODO = new StringBuffer(C0.toString() + D0.toString());//PC2置换StringBuffer C0D0tmp = new StringBuffer();for (int j = 0; j < 48; j++) {C0D0tmp.append(CODO.charAt(PC2[j] - 1));}subkey[i] = C0D0tmp;//  System.out.println(i + "轮密钥：" + subkey[i]);}return subkey;}

二、分组加密

实现了对任意长度的明文进行加密，实现这个功能需要引入一个分组数变量，用来记录分几组。

整个源代码如下：

package DES;import java.util.Scanner;public class Demo {private StringBuffer plaintext;  //明文字符串64 bits----8 bytesprivate StringBuffer ciphertext;  //密文字符串64 bits----8 bytesprivate StringBuffer key;  //密钥字符串64 bits ----8 bytesprivate int group;  //分组public int getGroup() {return group;}//设置分组数public void setGroup() {group = plaintext.length() / 8;}public StringBuffer getPlaintext() {return plaintext;}public void setPlaintext(StringBuffer plaintext) {this.plaintext = plaintext;}public StringBuffer getCiphertext() {return ciphertext;}public void setCiphertext(StringBuffer ciphertext) {this.ciphertext = ciphertext;}public StringBuffer getKey() {return key;}public void setKey(StringBuffer key) {this.key = key;}//IP置换private static final int[] IP = {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};//IP逆置换private static final int[] IPReverse = {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};// E位选择表(扩展置换表)private static final int[] E = {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换位表(单纯换位表)private static final int[] P = {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};//PC1private static final int[] PC1 = {57, 49, 41, 33, 25, 17, 9,1, 58, 50, 42, 34, 26, 18,10, 2, 59, 51, 43, 35, 27,19, 11, 3, 60, 52, 44, 36,63, 55, 47, 39, 31, 23, 15,7, 62, 54, 46, 38, 30, 22,14, 6, 61, 53, 45, 37, 29,21, 13, 5, 28, 20, 12, 4};// PC2private static final int[] PC2 = {14, 17, 11, 24, 1, 5,3, 28, 15, 6, 21, 10,23, 19, 12, 4, 26, 8,16, 7, 27, 20, 13, 2,41, 52, 31, 37, 47, 55,30, 40, 51, 45, 33, 48,44, 49, 39, 56, 34, 53,46, 42, 50, 36, 29, 32};// SBoxprivate static final int[][] SBox = {// S1{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},// S2{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},// S3{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},// S4{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},// S5{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},// S6{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},// S7{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},// S8{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}};//StringBuffer转成二进制public StringBuffer stringBufferToBinary(StringBuffer s) {StringBuffer res = new StringBuffer();StringBuffer stmp = new StringBuffer();for (int i = 0; i < s.length(); i++) {stmp = new StringBuffer(Integer.toBinaryString(s.charAt(i)));while (stmp.length() < 8) {  //转成8位二进制stmp.insert(0, 0);}//System.out.println(stmp);res.append(stmp);}return res;}//二进制字符串转成字符64->8//int column = Integer.parseInt(Sinput.substring(1, 5), 2);public StringBuffer BinaryTostringBuffer(StringBuffer s) {StringBuffer res = new StringBuffer();for (int i = 0; i < 8; i++) {int t = Integer.parseInt(s.substring(i * 8, (i + 1) * 8), 2);res.append((char) t);}return res;}//初始置换IPpublic StringBuffer Initial(StringBuffer r) {StringBuffer res = new StringBuffer();for (int i = 0; i < 64; i++) {res.append(r.charAt(IP[i] - 1)); //数组的索引是从0开始的}return res;}//终止置换IPpublic StringBuffer Final(StringBuffer r) {StringBuffer res = new StringBuffer();for (int i = 0; i < 64; i++) {res.append(r.charAt(IPReverse[i] - 1)); //数组的索引是从0开始的}return res;}//P置换public StringBuffer P(StringBuffer r) {StringBuffer res = new StringBuffer();for (int i = 0; i < 32; i++) {res.append(r.charAt(P[i] - 1)); //数组的索引是从0开始的}return res;}//扩展置换（E表）public StringBuffer Extent(StringBuffer r) {StringBuffer res = new StringBuffer();for (int i = 0; i < 48; i++) {res.append(r.charAt(E[i] - 1)); //数组的索引是从0开始的}return res;}//密钥生成public StringBuffer[] getSubkey() {StringBuffer keyBinary = new StringBuffer(stringBufferToBinary(key)); //把密钥转成二进制StringBuffer subkey[] = new StringBuffer[16];  //subkey数组用来存储子密钥StringBuffer C0 = new StringBuffer(); //左密钥StringBuffer D0 = new StringBuffer(); //右密钥//判断密钥长度while (keyBinary.length() < 64) {keyBinary.append("0");}//PC1置换（64 bits --> 56 bits）for (int i = 0; i < 28; i++) {C0.append(keyBinary.charAt(PC1[i] - 1));D0.append(keyBinary.charAt(PC1[i + 28] - 1));}//16轮循环生成子密钥//16轮移位操作，每轮左移一位，特殊情况左移两位（查看密钥移位表）for (int i = 0; i < 16; i++) {//把第一位删了添加到最后一位char tmp;tmp = C0.charAt(0);C0.deleteCharAt(0);C0.append(tmp);tmp = D0.charAt(0);D0.deleteCharAt(0);D0.append(tmp);//特殊位置左移两位if (i != 0 && i != 1 && i != 8 && i != 15) {tmp = C0.charAt(0);C0.deleteCharAt(0);C0.append(tmp);tmp = D0.charAt(0);D0.deleteCharAt(0);D0.append(tmp);}//左右合并StringBuffer CODO = new StringBuffer(C0.toString() + D0.toString());//PC2置换StringBuffer C0D0tmp = new StringBuffer();for (int j = 0; j < 48; j++) {C0D0tmp.append(CODO.charAt(PC2[j] - 1));}subkey[i] = C0D0tmp;//  System.out.println(i + "轮密钥：" + subkey[i]);}return subkey;}//f轮函数public StringBuffer F(StringBuffer R, StringBuffer subkey) {StringBuffer res = new StringBuffer();//E盒扩展res = Extent(R);//异或运算for (int i = 0; i < 48; i++) {res.replace(i, i + 1, (res.charAt(i) == subkey.charAt(i) ? "0" : "1"));}//S盒压缩StringBuffer sBox = new StringBuffer();  //sBox用来接收压缩后的32 bitsfor (int i = 0; i < 8; i++) {String Sinput = res.substring(i * 6, (i + 1) * 6);//首尾两位转化为行，中间四位转化为列//parseInt(String s,int radix)---把字符串s根据radix（进制）转成对应的整数int row = Integer.parseInt(Character.toString(Sinput.charAt(0)) + Sinput.charAt(5), 2);int column = Integer.parseInt(Sinput.substring(1, 5), 2);StringBuffer Soutput = new StringBuffer(Integer.toBinaryString(SBox[i][row * 16 + column]));while (Soutput.length() < 4) {//小于四位要添0Soutput.insert(0, 0);}sBox.append(Soutput);}//P置换sBox = P(sBox);return sBox;}//16轮迭代public StringBuffer iteration(StringBuffer L, StringBuffer R, int mode) {StringBuffer res = new StringBuffer();StringBuffer[] subkey = getSubkey(); //获取子密钥//mode == 1 解密  密钥反转if (mode == 1) {StringBuffer[] tmp = getSubkey();  //mode ==1for (int i = 0; i < 16; i++) {subkey[i] = tmp[15 - i];//  System.out.println(i+"轮密钥："+subkey[i]);}}//查看密钥
//        for (int i =0;i<16;i++){
//            System.out.println(i+"轮密钥："+subkey[i]);
//        }//16轮循环for (int i = 0; i < 16; i++) {StringBuffer Ltmp = new StringBuffer(L);StringBuffer Rtmp = new StringBuffer(R);//右边的赋给左边L.replace(0, 32, R.toString());//F轮函数StringBuffer Fstring = F(Rtmp, subkey[i]);//Fstring异或Rfor (int j = 0; j < 32; j++) {R.replace(j, j + 1, (Fstring.charAt(j) == Ltmp.charAt(j) ? "0" : "1"));}}//循环结束后左右交换StringBuffer RL = new StringBuffer(R.toString() + L.toString());//终止置换RL = Final(RL);return RL;}public static void main(String[] args) {System.out.println("----DES----");Demo instance = new Demo();//创建实例StringBuffer plain = new StringBuffer(); //录入明文String tmp = ""; //用来临时录入明文密文Scanner sc = new Scanner(System.in);System.out.println("请输入明文：");tmp = sc.next();plain.append(tmp);int length = plain.length(); //保存明文的长度instance.setPlaintext(plain);System.out.println("明文：" + instance.getPlaintext());//密钥产生System.out.println("输入密钥：");tmp = sc.next();StringBuffer mykey = new StringBuffer();mykey.append(tmp);instance.setKey(mykey);System.out.println("密钥：" + instance.getKey());//设置分组数instance.setGroup();//测试加密System.out.println("-----DES加密-----");plain = instance.stringBufferToBinary(instance.getPlaintext()); //明文转成二进制StringBuffer L = new StringBuffer();//左明文StringBuffer R = new StringBuffer();//右明文StringBuffer plainBackup = new StringBuffer(plain);  //二进制明文备份StringBuffer cipherBackup = new StringBuffer();  //二进制密文备份StringBuffer descipher = new StringBuffer(); //解密后的明文//扩充明文while (plainBackup.length() < 64 * (instance.group + 1)) {plainBackup.append("0");}//分组加密for (int i = 0; i <= instance.group; i++) {//明文分组处理for (int j = 0; j < 64; j++) {plain.replace(j, j + 1, plainBackup.substring(j + i * 64, j + 64 * i + 1));}//初始置换plain = instance.Initial(plain);L.replace(0, 32, plain.substring(0, 32));R.replace(0, 32, plain.substring(32, 64));//16轮迭代plain = instance.iteration(L, R, 0);//plain是加密后的二进制密文System.out.println(i + "轮迭代后：" + plain);//备份二进制密文cipherBackup.append(plain);System.out.println(i + "轮密文：" + instance.BinaryTostringBuffer(plain));}//测试解密System.out.println("-----DES解密-----");//分组解密for (int i = 0; i <= instance.group; i++) {//密文分组处理for (int j = 0; j < 64; j++) {plain.replace(j, j + 1, cipherBackup.substring(j + i * 64, j + 64 * i + 1));}//初始置换plain = instance.Initial(plain);L.replace(0, 32, plain.substring(0, 32));R.replace(0, 32, plain.substring(32, 64));plain = instance.iteration(L, R, 1);//plain是解密后的二进制密文System.out.println(i + "轮迭代后：" + plain);System.out.println(i + "明文：" + instance.BinaryTostringBuffer(plain));descipher.append(instance.BinaryTostringBuffer(plain));}//输出解密后的明文System.out.println("最终解密后的明文："+descipher.substring(0,length));}
}
/*
aaaaaaaa
-----------
abcdef
abcdabcd:
abcdabcd:
----------
abcdefgh
abcdefghijkabcdefghijk*/

三、运行结果

明文长度小于8比特，密钥长度小于8。

明文长度大于8比特。

DES实现的粗略版链接：DES算法的Java实现（粗略版）_争取不划水的博客-CSDN博客

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DES算法Java实现（完善版）

一、密钥长度处理

二、分组加密

三、运行结果

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