详解DES加密算法及在Java程序中的使用示例

des加密算法
des全称为data encryption standard，即数据加密标准，是一种使用密钥加密的块算法，1976年被美国联邦*的国家标准局确定为联邦资料处理标准（fips），随后在国际上广泛流传开来。
des算法的入口参数有三个:key、data、mode。其中key为7个字节共56位,是des算法的工作密钥;data为8个字节64位,是要被加密或被解密的数据;mode为des的工作方式,有两种:加密或解密。
des算法把64位的明文输入块变为64位的密文输出块,它所使用的密钥也是56位，其算法主要分为两步：
1）初始置换
其功能是把输入的64位数据块按位重新组合,并把输出分为l0、r0两部分,每部分各长32位,其置换规则为将输入的第58位换到第一位,第50位换到第2位……依此类推,最后一位是原来的第7位。l0、r0则是换位输出后的两部分，l0是输出的左32位,r0是右32位,例:设置换前的输入值为d1d2d3……d64,则经过初始置换后的结果为:l0=d58d50……d8;r0=d57d49……d7。
其置换规则见下表：

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,

2）逆置换
经过16次迭代运算后,得到l16、r16,将此作为输入,进行逆置换,逆置换正好是初始置换的逆运算，由此即得到密文输出。
此算法是对称加密算法体系中的代表,在计算机网络系统中广泛使用.

java基本实现

package com.stone.security; 
 
import java.security.key; 
import java.security.securerandom; 
 
import javax.crypto.cipher; 
import javax.crypto.keygenerator; 
import javax.crypto.secretkey; 
import javax.crypto.secretkeyfactory; 
import javax.crypto.spec.deskeyspec; 
import javax.crypto.spec.ivparameterspec; 
 
/** 
 * des 算法    1972美国ibm研制，对称加密算法 
 */ 
public class des {  
  // 算法名称 
  public static final string key_algorithm = "des"; 
  // 算法名称/加密模式/填充方式 
  public static final string cipher_algorithm_ecb = "des/ecb/pkcs5padding"; 
  public static final string cipher_algorithm_cbc = "des/cbc/pkcs5padding"; 
   
  public static void main(string[] args) throws exception { 
    /* 
     * 使用 ecb mode 
     * 密钥生成器 生成密钥 
     * ecb mode cannot use iv 
     */ 
    byte[] key = generatekey();  
    byte[] encrypt = encrypt("胃炎f#*（x）".getbytes(), key); 
    system.out.println(new string(decrypt(encrypt, key))); 
     
     
    /* 
     * 使用cbc mode 
     * 使用密钥工厂生成密钥，加密 解密 
     * iv: des in cbc mode and rsa ciphers with oaep encoding operation. 
     */ 
    deskeyspec dks = new deskeyspec(generatekey()); 
    secretkeyfactory factory = secretkeyfactory.getinstance(key_algorithm); 
    secretkey secretkey = factory.generatesecret(dks); 
    cipher cipher = cipher.getinstance(cipher_algorithm_cbc); 
    cipher.init(cipher.encrypt_mode, secretkey, new ivparameterspec(getiv())); 
    byte[] enc = cipher.dofinal("胃炎a%f#*（x）".getbytes()); //加密 
     
    cipher.init(cipher.decrypt_mode, secretkey, new ivparameterspec(getiv())); 
    byte[] dec = cipher.dofinal(enc); // 解密 
    system.out.println(new string(dec)); 
  } 
   
  static byte[] getiv() { 
    string iv = "asdfivh7"; //iv length: must be 8 bytes long 
    return iv.getbytes(); 
  } 
 
  /** 
   * 生成密钥 
   * 
   * @return 
   * @throws exception 
   */ 
  private static byte[] generatekey() throws exception { 
    keygenerator keygenerator = keygenerator.getinstance(key_algorithm); 
    keygenerator.init(56); //des 必须是56, 此初始方法不必须调用 
    secretkey secretkey = keygenerator.generatekey(); 
    return secretkey.getencoded(); 
  } 
 
  /** 
   * 还原密钥 
   * 
   * @param key 
   * @return 
   * @throws exception 
   */ 
  private static key tokey(byte[] key) throws exception { 
    deskeyspec des = new deskeyspec(key); 
    secretkeyfactory keyfactory = secretkeyfactory.getinstance(key_algorithm); 
    secretkey secretkey = keyfactory.generatesecret(des); 
    return secretkey; 
  } 
   
  /** 
   * 加密 
   * @param data 原文 
   * @param key 
   * @return 密文 
   * @throws exception 
   */ 
  public static byte[] encrypt(byte[] data, byte[] key) throws exception { 
    key k = tokey(key); 
    cipher cipher = cipher.getinstance(cipher_algorithm_ecb); 
    cipher.init(cipher.encrypt_mode, k, new securerandom()); 
    return cipher.dofinal(data); 
  } 
  /** 
   * 解密 
   * @param data 密文 
   * @param key 
   * @return 明文、原文 
   * @throws exception 
   */ 
  public static byte[] decrypt(byte[] data, byte[] key) throws exception { 
    key k = tokey(key); 
    cipher cipher = cipher.getinstance(cipher_algorithm_ecb); 
    cipher.init(cipher.decrypt_mode, k, new securerandom()); 
    return cipher.dofinal(data); 
  } 
} 

java三重des实现：

package com.stone.security; 
 
import javax.crypto.cipher; 
import javax.crypto.keygenerator; 
import javax.crypto.secretkey; 
import javax.crypto.secretkeyfactory; 
import javax.crypto.spec.desedekeyspec; 
import javax.crypto.spec.ivparameterspec; 
 
/** 
 * 三重加密 3des也作 triple des, 
 */ 
public class tripledes { 
  // 算法名称 
  public static final string key_algorithm = "desede"; 
  // 算法名称/加密模式/填充方式 
  public static final string cipher_algorithm_ecb = "desede/ecb/pkcs5padding"; 
  public static final string cipher_algorithm_cbc = "desede/cbc/pkcs5padding"; 
   
  private keygenerator keygen; 
  private secretkey secretkey; 
  private secretkey secretkey2; 
  private cipher cipher; 
  private static byte[] encryptdata; 
   
  public static void main(string[] args) throws exception { 
    tripledes tripledes = new tripledes("ecb"); 
    tripledes.encrypt("sau8jzxlcvm,'123`98(*^&%^^jcb zx>>a<s<}}{"); 
    system.out.println("加密后：" + new string(encryptdata)); 
    system.out.println("解密后："+ new string(tripledes.decrypt(encryptdata))); 
     
    tripledes = new tripledes("cbc"); 
    tripledes.encrypt2("sau8jzxlc dqv#><«|vm,'123`98(*^&%^^jcb zx>>a<s<}}{"); 
    system.out.println("加密后：" + new string(encryptdata)); 
    system.out.println("解密后："+ new string(tripledes.decrypt2(encryptdata))); 
  } 
   
  public tripledes(string mode) throws exception { 
    if ("ecb".equals(mode)) { 
//     cipher = cipher.getinstance(key_algorithm); 
      cipher = cipher.getinstance(cipher_algorithm_ecb); 
      keygen = keygenerator.getinstance(key_algorithm); 
      secretkey = keygen.generatekey(); 
    } else if("cbc".equals(mode)) { 
      cipher = cipher.getinstance(cipher_algorithm_cbc); 
      keygen = keygenerator.getinstance(key_algorithm); 
      desedekeyspec spec = new desedekeyspec(keygen.generatekey().getencoded()); 
      secretkey2 = secretkeyfactory.getinstance(key_algorithm).generatesecret(spec); 
    } 
  } 
  /** 
   * 加密 
   * @param str 
   * @return 
   * @throws exception 
   */ 
  public byte[] encrypt(string str) throws exception { 
    cipher.init(cipher.encrypt_mode, secretkey); 
    return encryptdata = cipher.dofinal(str.getbytes()); 
  } 
  /** 
   * 解密 
   * @param encrypt 
   * @return 
   * @throws exception 
   */ 
  public byte[] decrypt(byte[] encrypt) throws exception { 
    cipher.init(cipher.decrypt_mode, secretkey); 
    return encryptdata = cipher.dofinal(encrypt); 
  } 
  byte[] getiv() { 
    return "administ".getbytes(); 
  } 
  /** 
   * 加密 
   * @param str 
   * @return 
   * @throws exception 
   */ 
  public byte[] encrypt2(string str) throws exception { 
    cipher.init(cipher.encrypt_mode, secretkey2, new ivparameterspec(getiv())); 
    return encryptdata = cipher.dofinal(str.getbytes()); 
  } 
  /** 
   * 解密 
   * @param encrypt 
   * @return 
   * @throws exception 
   */ 
  public byte[] decrypt2(byte[] encrypt) throws exception { 
    cipher.init(cipher.decrypt_mode, secretkey2, new ivparameterspec(getiv())); 
    return encryptdata = cipher.dofinal(encrypt); 
  } 
}