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基本介绍

分组密码，也叫块加密(block cyphers)，一次加密明文中的一个块。将明文按一定的位长分组，明文组经过加密运算得到密文组。将多个密文组合并成密文。密文组经过解密运算（加密运算的逆运算），还原成明文组。

序列密码，也叫流加密(stream cyphers)，一次加密明文中的一个位。利用少量的密钥（制乱元素）通过某种复杂的运算（密码算法）产生大量的伪随机位流，用于对明文位流的加密。也可以用同样的密钥和密码算法及与加密相同的伪随机位流，用以还原明文位流。

四种分组加密模式

图片来源:

ECB(Electronic Code Book)/电码本模式

ECB模式是最简单的一种，从图中就可以看出，就是利用一个密钥KEY分别对每个明文块进行加密，解密就是逆过程，同时可以发现每个明文块加密过程是相互独立的，可以并行，所以加密效率是最快的。

CBC(Cipher Block Chaining)/密文分组链接方式

CBC模式与之前的ECB加密过程差不多，只不过每个明文块的加密密钥依赖于前一个明文加密后的结果，所以不能并行处理。

Cipher Feedback (CFB)/密文反馈模式

CFB模式就是对初始化向量IV进行加密再与明文异或来得到密文，再利用得到的密文作为下一个明文加密的密钥。

Output Feedback (OFB)/输出反馈模式

OFB模式与CFB模式的加密过程类似，不过OFB模式是对明文加密后再进行的异或操作。这个模式最神奇的地方是加密和解密的过程是一样的，你可以查看下面Java实现CFB的加解密函数，是一模一样的。

代码实现

代码中实现了对普通字节数组的加/解密,还实现了对图片加解密。对图片的加解密是利用直接内存实现的。处理效率高，可以减少一次从操作系统到JVM的IO

import javax.crypto.Cipher;import javax.crypto.SecretKey;import javax.crypto.SecretKeyFactory;import javax.crypto.spec.DESKeySpec;import javax.swing.filechooser.FileSystemView;import java.io.File;import java.io.FileInputStream;import java.io.FileOutputStream;import java.nio.ByteBuffer;import java.nio.channels.FileChannel;import java.util.Arrays;public class PacketSecret {
       private OperationMode mode;//要使用的加密运行模式    private SecretKey secretKey;//DES使用的密钥    private Cipher enCipher, deCipher;//加密/解密算法,这里选用DES    private static final byte[] IV = {
   1, 2, 3, 4, 5, 6, 7, 8};    private static byte count;//记录填充数    public PacketSecret() {
           this(new ECB());    }    public PacketSecret(OperationMode mode) {
           this.mode = mode;        initDES();    }    public void setMode(OperationMode mode) {
           this.mode = mode;    }    public OperationMode getMode() {
           return mode;    }    //初始化密钥和加密算法    private void initDES() {
           try {
               //原始密钥，至少8个            byte[] rawKey = new byte[]{
   1, 2, 3, 4, 5, 6, 7, 8};            DESKeySpec deskeySpec = new DESKeySpec(rawKey);            secretKey = SecretKeyFactory.getInstance("DES").generateSecret(deskeySpec);            enCipher = Cipher.getInstance("DES/ECB/NoPadding");//这里只使用普通的DES模式            deCipher = Cipher.getInstance("DES/ECB/NoPadding");            enCipher.init(Cipher.ENCRYPT_MODE, secretKey);            deCipher.init(Cipher.DECRYPT_MODE, secretKey);        } catch (Exception e) {
               System.out.println("DES算法初始化失败");            e.printStackTrace();        }    }    //对分组数据预处理，以输入加密函数    private byte[] initPacket(byte[] data) {
           if (data.length % 8 == 0) return data;        //如果刚好64一组则直接进行加密，否则先填充        byte[] newData = new byte[((data.length >> 3) + 1) * 8];        System.arraycopy(data, 0, newData, 0, data.length);//默认填充0        count = (byte) (8 - data.length % 8);//记录填充了多少数据        return newData;    }    public byte[] packetEncrypt(byte[] data) {
           byte[] packets = initPacket(data);        try {
               byte[] encryptData = mode.packetEncrypt(packets, enCipher);            return encryptData;        } catch (Exception e) {
               e.printStackTrace();        }        return null;    }    public byte[] packetDecrypt(byte[] packets) {
           if (packets.length % 8 != 0) {
               System.out.println("解密数据长度错误");            return null;        }        try {
               byte[] rawData = mode.packetDecrypt(packets, deCipher, enCipher);            if (count == 0) {
                   return rawData;            } else {
                   return Arrays.copyOf(rawData, rawData.length - count);            }        } catch (Exception e) {
               e.printStackTrace();        }        return null;    }    private static void arraysXOR(byte[] src, byte[] des) {
           if (src.length != des.length) {
               System.out.println("数组长度不一致无法异或");            return;        }        for (int i = 0; i < src.length; i++) {
               src[i] ^= des[i];        }    }    static class ECB implements OperationMode {
           @Override        public byte[] packetEncrypt(byte[] data, Cipher enCipher) throws Exception {
               byte[] encryptData = new byte[data.length];            byte[] encryptBlock, block;            //循环加密，每8字节一组            for (int i = 0; i < data.length; i += 8) {
                   block = Arrays.copyOfRange(data, i, i + 8);//获取分组                encryptBlock = enCipher.doFinal(block);//进行加密                //将数据拷贝到输出数组                System.arraycopy(encryptBlock, 0, encryptData, i, encryptBlock.length);            }            return encryptData;        }        @Override        public byte[] packetDecrypt(byte[] data, Cipher deCipher, Cipher enCipher) throws Exception {
               byte[] rawData = new byte[data.length];            byte[] decryptBlock, block;            //循环加密，每8字节一组            for (int i = 0; i < data.length; i += 8) {
                   block = Arrays.copyOfRange(data, i, i + 8);//获取分组                decryptBlock = deCipher.doFinal(block);//进行解密                //将数据拷贝到输出数组                System.arraycopy(decryptBlock, 0, rawData, i, decryptBlock.length);            }            return rawData;        }    }    static class CBC implements OperationMode {
           @Override        public byte[] packetEncrypt(byte[] data, Cipher enCipher) throws Exception {
               byte[] encryptData = new byte[data.length];            byte[] encryptBlock, block;            byte[] iv = Arrays.copyOf(IV, IV.length);            //循环加密，每8字节一组            for (int i = 0; i < data.length; i += 8) {
                   block = Arrays.copyOfRange(data, i, i + 8);//获取分组                arraysXOR(block, iv);//保存异或结果到block                encryptBlock = enCipher.doFinal(block);//对结果进行加密                iv = encryptBlock;//保存结果加密到iv                //将数据拷贝到输出数组                System.arraycopy(encryptBlock, 0, encryptData, i, encryptBlock.length);            }            return encryptData;        }        @Override        public byte[] packetDecrypt(byte[] data, Cipher deCipher, Cipher enCipher) throws Exception {
               byte[] rawData = new byte[data.length];            byte[] decryptBlock, block;            byte[] iv = Arrays.copyOf(IV, IV.length);            //循环加密，每8字节一组            for (int i = 0; i < data.length; i += 8) {
                   block = Arrays.copyOfRange(data, i, i + 8);//获取分组                decryptBlock = deCipher.doFinal(block);//先进行解密                arraysXOR(decryptBlock, iv);//将异或结果保存到decryptBlock                iv = block;                //将数据拷贝到输出数组                System.arraycopy(decryptBlock, 0, rawData, i, decryptBlock.length);            }            return rawData;        }    }    static class CFB implements OperationMode {
           @Override        public byte[] packetEncrypt(byte[] data, Cipher enCipher) throws Exception {
               byte[] encryptData = new byte[data.length];            byte[] encryptBlock, block;            byte[] iv = Arrays.copyOf(IV, IV.length);            //循环加密，每8字节一组            for (int i = 0; i < data.length; i += 8) {
                   block = Arrays.copyOfRange(data, i, i + 8);//获取分组                encryptBlock = enCipher.doFinal(iv);//对IV进行加密                arraysXOR(encryptBlock, block);//保存异或结果到encryptBlock                iv = encryptBlock;//保存密文结果到iv                //将数据拷贝到输出数组                System.arraycopy(encryptBlock, 0, encryptData, i, encryptBlock.length);            }            return encryptData;        }        @Override        public byte[] packetDecrypt(byte[] data, Cipher deCipher, Cipher enCipher) throws Exception {
               byte[] rawData = new byte[data.length];            byte[] decryptBlock, block;            byte[] iv = Arrays.copyOf(IV, IV.length);            //循环加密，每8字节一组            for (int i = 0; i < data.length; i += 8) {
                   block = Arrays.copyOfRange(data, i, i + 8);//获取分组                iv = enCipher.doFinal(iv);//获取到加密后的IV                arraysXOR(block, iv);//先将异或结果保存到Block                decryptBlock = block;                iv = Arrays.copyOfRange(data, i, i + 8);                //将数据拷贝到输出数组                System.arraycopy(decryptBlock, 0, rawData, i, decryptBlock.length);            }            return rawData;        }    }    static class OFB implements OperationMode {
           @Override        public byte[] packetEncrypt(byte[] data, Cipher enCipher) throws Exception {
               byte[] encryptData = new byte[data.length];            byte[] encryptBlock, block;            byte[] iv = Arrays.copyOf(IV, IV.length);            //循环加密，每8字节一组            for (int i = 0; i < data.length; i += 8) {
                   block = Arrays.copyOfRange(data, i, i + 8);//获取分组                iv = enCipher.doFinal(iv);//对IV进行加密                encryptBlock = Arrays.copyOf(iv, iv.length);                arraysXOR(encryptBlock, block);//保存异或结果到encryptBlock                //将数据拷贝到输出数组                System.arraycopy(encryptBlock, 0, encryptData, i, encryptBlock.length);            }            return encryptData;        }        @Override        public byte[] packetDecrypt(byte[] data, Cipher deCipher, Cipher enCipher) throws Exception {
               //OFB模式下加解密过程是一致的            return packetEncrypt(data, enCipher);        }    }    public static void printArrays(byte[] data) {
           for (int i = 0; i < data.length; i++) {
               System.out.print(String.format("0x%02x,", data[i]));        }        System.out.println();    }    public static void imageTest(File infile, File outFile, Mode mode) {
           PacketSecret secret = new PacketSecret();        secret.setMode(new ECB());        try (//自动关闭流             FileInputStream fis = new FileInputStream(infile);             FileOutputStream fos = new FileOutputStream(outFile);        ) {
               FileChannel infileChannel = fis.getChannel();            FileChannel outfileChannel = fos.getChannel();            ByteBuffer byteBuffer = ByteBuffer.allocate(1024 * 5);//读入5k到缓冲区            byte[] secretText;            while (infileChannel.read(byteBuffer) != -1) {
   //读取到缓冲区                byte[] data = byteBuffer.array();                if (mode == Mode.Encrypt) {
                       secretText = secret.packetEncrypt(data);                } else {
                       secretText = secret.packetDecrypt(data);                }                byteBuffer.rewind();//将指针指向头部                byteBuffer.put(secretText);                byteBuffer.flip();//设置limit指针到position，准备读出                outfileChannel.write(byteBuffer);                byteBuffer.clear();            }            infileChannel.close();            outfileChannel.close();        } catch (Exception e) {
               e.printStackTrace();        }    }    public static void simpleTest() {
           byte[] text = new byte[]{
   0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13};//明文内容        PacketSecret secret = new PacketSecret();        secret.setMode(new ECB());        test(secret, text);        secret.setMode(new CBC());        test(secret, text);        secret.setMode(new CFB());        test(secret, text);        secret.setMode(new OFB());        test(secret, text);    }    public static void test(PacketSecret secret, byte[] text) {
           System.out.println("-------当前运行模式:" + secret.getMode().getClass().getSimpleName() + "-------");        byte[] pe = secret.packetEncrypt(text);        System.out.println("----密文如下:----");        printArrays(pe);        System.out.println("----解密后如下:----");        printArrays(secret.packetDecrypt(pe));    }    public static void main(String[] args) {
   //        simpleTest();//字节数组测试        //在桌面放一张名为test.jpg的图片        System.out.println("在桌面放一张名为test.jpg的图片");        File file = new File(FileSystemView.getFileSystemView().getHomeDirectory(), "test.jpg");        //输出到桌面        File EncryptFile = new File(FileSystemView.getFileSystemView().getHomeDirectory(), "test-Encrypt.jpg");        File DecryptFile = new File(FileSystemView.getFileSystemView().getHomeDirectory(), "test-Decrypt.jpg");        System.out.println("加密图片文件路径:" + EncryptFile.getPath());        imageTest(file, EncryptFile, Mode.Encrypt);//输出加密图片        imageTest(EncryptFile, DecryptFile, Mode.Decrypt);//输出解密图片    }    enum Mode {
   Decrypt, Encrypt}    //运作模式通用接口，采用"命令设计模式"    public interface OperationMode {
           byte[] packetEncrypt(byte[] data, Cipher cipher) throws Exception;//加密分组        byte[] packetDecrypt(byte[] data,Cipher deCipher,Cipher enCipher) throws Exception;//解密分组    }}

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