Java MD5消息摘要算法原理及实现代码

/** 
   * MD5 32bit Encrypt Methods. 
   * @param readyEncryptStr ready encrypt string 
   * @return String encrypt result string 
   * @throws NoSuchAlgorithmException 
   * */ 
  public static final String MD5_32bit(String readyEncryptStr) throws NoSuchAlgorithmException{ 
    if(readyEncryptStr != null){ 
      //Get MD5 digest algorithm's MessageDigest's instance. 
      MessageDigest md = MessageDigest.getInstance("MD5"); 
      //Use specified byte update digest. 
      md.update(readyEncryptStr.getBytes()); 
      //Get cipher text 
      byte [] b = md.digest(); 
      //The cipher text converted to hexadecimal string 
      StringBuilder su = new StringBuilder(); 
      //byte array switch hexadecimal number. 
      for(int offset = 0,bLen = b.length; offset < bLen; offset++){ 
        String haxHex = Integer.toHexString(b[offset] & 0xFF); 
        if(haxHex.length() < 2){ 
          su.append("0"); 
        } 
        su.append(haxHex); 
      } 
      return su.toString(); 
    }else{ 
      return null; 
    } 
  }

public class MD5{
  /*
  *四个链接变量
  */
  private final int A=0x67452301;
  private final int B=0xefcdab89;
  private final int C=0x98badcfe;
  private final int D=0x10325476;
  /*
  *ABCD的临时变量
  */
  private int Atemp,Btemp,Ctemp,Dtemp;
   
  /*
  *常量ti
  *公式:floor(abs(sin(i+1))×(2pow32)
  */
  private final int K[]={
    0xd76aa478,0xe8c7b756,0x242070db,0xc1bdceee,
    0xf57c0faf,0x4787c62a,0xa8304613,0xfd469501,0x698098d8,
    0x8b44f7af,0xffff5bb1,0x895cd7be,0x6b901122,0xfd987193,
    0xa679438e,0x49b40821,0xf61e2562,0xc040b340,0x265e5a51,
    0xe9b6c7aa,0xd62f105d,0x02441453,0xd8a1e681,0xe7d3fbc8,
    0x21e1cde6,0xc33707d6,0xf4d50d87,0x455a14ed,0xa9e3e905,
    0xfcefa3f8,0x676f02d9,0x8d2a4c8a,0xfffa3942,0x8771f681,
    0x6d9d6122,0xfde5380c,0xa4beea44,0x4bdecfa9,0xf6bb4b60,
    0xbebfbc70,0x289b7ec6,0xeaa127fa,0xd4ef3085,0x04881d05,
    0xd9d4d039,0xe6db99e5,0x1fa27cf8,0xc4ac5665,0xf4292244,
    0x432aff97,0xab9423a7,0xfc93a039,0x655b59c3,0x8f0ccc92,
    0xffeff47d,0x85845dd1,0x6fa87e4f,0xfe2ce6e0,0xa3014314,
    0x4e0811a1,0xf7537e82,0xbd3af235,0x2ad7d2bb,0xeb86d391};
  /*
  *向左位移数,计算方法未知
  */
  private final int s[]={7,12,17,22,7,12,17,22,7,12,17,22,7,
    12,17,22,5,9,14,20,5,9,14,20,5,9,14,20,5,9,14,20,
    4,11,16,23,4,11,16,23,4,11,16,23,4,11,16,23,6,10,
    15,21,6,10,15,21,6,10,15,21,6,10,15,21};
   
   
  /*
  *初始化函数
  */
  private void init(){
    Atemp=A;
    Btemp=B;
    Ctemp=C;
    Dtemp=D;
  }
  /*
  *移动一定位数
  */
  private  int  shift(int a,int s){
    return(a<<s)|(a>>>(32-s));//右移的时候，高位一定要补零，而不是补充符号位
  }
  /*
  *主循环
  */
  private void MainLoop(int M[]){
    int F,g;
    int a=Atemp;
    int b=Btemp;
    int c=Ctemp;
    int d=Dtemp;
    for(int i = 0; i < 64; i ++){
      if(i<16){
        F=(b&c)|((~b)&d);
        g=i;
      }else if(i<32){
        F=(d&b)|((~d)&c);
        g=(5*i+1)%16;
      }else if(i<48){
        F=b^c^d;
        g=(3*i+5)%16;
      }else{
        F=c^(b|(~d));
        g=(7*i)%16;
      }
      int tmp=d;
      d=c;
      c=b;
      b=b+shift(a+F+K[i]+M[g],s[i]);
      a=tmp;
    }
    Atemp=a+Atemp;
    Btemp=b+Btemp;
    Ctemp=c+Ctemp;
    Dtemp=d+Dtemp;
   
  }
  /*
  *填充函数
  *处理后应满足bits≡448(mod512),字节就是bytes≡56（mode64)
  *填充方式为先加一个0,其它位补零
  *最后加上64位的原来长度
  */
  private int[] add(String str){
    int num=((str.length()+8)/64)+1;//以512位，64个字节为一组
    int strByte[]=new int[num*16];//64/4=16，所以有16个整数
    for(int i=0;i<num*16;i++){//全部初始化0
      strByte[i]=0;
    }
    int  i;
    for(i=0;i<str.length();i++){
      strByte[i>>2]|=str.charAt(i)<<((i%4)*8);//一个整数存储四个字节，小端序
    }
    strByte[i>>2]|=0x80<<((i%4)*8);//尾部添加1
    /*
    *添加原长度，长度指位的长度，所以要乘8，然后是小端序，所以放在倒数第二个,这里长度只用了32位
    */
    strByte[num*16-2]=str.length()*8;
      return strByte;
  }
  /*
  *调用函数
  */
  public String getMD5(String source){
    init();
    int strByte[]=add(source);
    for(int i=0;i<strByte.length/16;i++){
    int num[]=new int[16];
    for(int j=0;j<16;j++){
      num[j]=strByte[i*16+j];
    }
    MainLoop(num);
    }
    return changeHex(Atemp)+changeHex(Btemp)+changeHex(Ctemp)+changeHex(Dtemp);
   
  }
  /*
  *整数变成16进制字符串
  */
  private String changeHex(int a){
    String str="";
    for(int i=0;i<4;i++){
      str+=String.format("%2s", Integer.toHexString(((a>>i*8)%(1<<8))&0xff)).replace(' ', '0');
 
    }
    return str;
  }
  /*
  *单例
  */
  private static MD5 instance;
  public static MD5 getInstance(){
    if(instance==null){
      instance=new MD5();
    }
    return instance;
  }
   
  private MD5(){};
   
  public static void main(String[] args){
    String str=MD5.getInstance().getMD5("");
    System.out.println(str);
  }
}