MD5算法的Java实现

//使用MD5算法对密码加密之后，会得到一个唯一的并且是不可逆转的字符串编码
//将加密后所得到的字符串编码作为密码标识符存储在数据库中，可以防止密码在数据库中被
//并且加密后的字符串编码是不能再转换到原有密码，这就保证了存储在数据库中的密码的安全性
//所以在用户校验时，不能直接把登录密码和数据库中存储的密码标识符进行比较
//而是需要将用户的登录密码也进行MD5转换，然后才可以进行比较
//下面的代码就实现了MD5算法对字符串进行加密的功能

/**
 * 实现了MD5算法对字符串进行加密的功能
 * @see 直接调用MD5类中的toMD5()方法
 * @see 即可对需要加密的字符串进行加密
 */
public class MD5 {
	//下面这些S11-S44实际上是一个4*4的矩阵，在原始的C实现中是用#define实现的
	//这里把它们实现成为static final是表示只读，且能在同一个进程空间内的多个Instance间共享
	static final int S11 = 7;
	static final int S12 = 12;
	static final int S13 = 17;
	static final int S14 = 22;
	static final int S21 = 5;
	static final int S22 = 9;
	static final int S23 = 14;
	static final int S24 = 20;
	static final int S31 = 4;
	static final int S32 = 11;
	static final int S33 = 16;
	static final int S34 = 23;
	static final int S41 = 6;
	static final int S42 = 10;
	static final int S43 = 15;
	static final int S44 = 21;
	static final byte[] PADDING = {-128, 0, 0, 0, 0, 0, 0, 0, 0, 
		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
	
	/**
	 * 下面的3个成员是MD5计算过程中用到的3个核心数据，在原始的C实现中被定义到MD5_CTX结构中
	 */
	private long[] state = new long[4]; //state()
	private long[] count = new long[2]; //number of bits, modulo 2^64 (Isb first)
	private byte[] buffer = new byte[64]; //input buffer
	
	//digestHexStr是MD5.java的唯一一个公共成员，是最新一次计算结果的十六进制ASCII表示
	//即此变量中存放了将输入串进行MD5运算后的128位MD5码的ASCII码�
	public String digestHexStr;
	
	//digest是最新一次计算结果的二进制内部表示，表示128bit的MD5值
	private byte[] digest = new byte[16];
	
	/**
	 * 这是类MD5最主要的公共方法
	 * @param inbuf 入口参数是你想要进行MD5变换的字符串
	 * @return 返回变换完的结果，该结果是从公共成员digestHexStr取得的
	 */
	public String getMD5ofStr(String inbuf){
		md5Init();
		md5Update(inbuf.getBytes(), inbuf.length());
		md5Final();
		digestHexStr = "";
		for(int i=0; i<16; i++){
			digestHexStr += byteHEX(digest[i]);
		}
		return digestHexStr;
	}
	
	/**
	 * 这是MD5类的标准构造函数，JavaBean要求有一个public的并且没有参数的构造函数
	 */
	public MD5(){
		md5Init();
		return;
	}
	
	/**
	 * 这是一个初始化函数，初始化核心变量，装入标准的函数
	 */
	private void md5Init(){
		count[0] = 0L;
		count[1] = 0L;
		//Load magic initialization constants
		state[0] = 0x67452301L;
		state[1] = 0xefcdab89L;
		state[2] = 0x98badcfeL;
		state[3] = 0x10325476L;
	}
	
	//F, G, H, I是4个基本的MD5函数
	//在原始的MD5的C实现中，由于它们是简单的位运算，可能出于效率的考虑把它们实现成了宏
	//在Java中，我们把它们实现成了private方法，名字保持了原来C中的
	private long F(long x, long y, long z){
		return (x&y) | ((~x)&z);
	}
	private long G(long x, long y, long z){
		return (x&z) | (y&(~z));
	}
	private long H(long x, long y, long z){
		return x ^ y ^ z;
	}
	private long I(long x, long y, long z){
		return y ^ (x | (~z));
	}
	
	//FF, GG, HH和II将调用F, G, H, I进行进一步变换
	//FF, GG, HH and II transformations for rounds 1,2,3 and 4
	//Rotation is separate from addition to prevent recomputation
	private long FF(long a, long b, long c, long d, long x, long s, long ac){
		a += F(b, c, d) + x + ac;
		a = ((int)a << s) | ((int)a >>> (32-s));
		a += b;
		return a;
	}
	private long GG(long a, long b, long c, long d, long x, long s, long ac){
		a += G(b, c, d) + x + ac;
		a = ((int)a << s) | ((int)a >>> (32-s));
		a += b;
		return a;
	}
	private long HH(long a, long b, long c, long d, long x, long s, long ac){
		a += H(b, c, d) + x + ac;
		a = ((int)a << s) | ((int)a >>> (32-s));
		a += b;
		return a;
	}
	private long II(long a, long b, long c, long d, long x, long s, long ac){
		a += I(b, c, d) + x + ac;
		a = ((int)a << s) | ((int)a >>> (32-s));
		a += b;
		return a;
	}
	
	/**
	 * 这是MD5的主计算过程。该函数由getMD5ofStr调用
	 * @see 该函数在被调用之前需要调用md5Init，因此把它设计成private的
	 * @param inbuf 要进行MD5加密的字节串
	 * @param inputLen 字符串长度
	 */
	private void md5Update(byte[] inbuf, int inputLen){
		int i, index, partLen;
		byte[] block = new byte[64];
		index = (int)(count[0]>>>3) & 0x3F;
		//Update number of bits
		if((count[0] += (inputLen<<3)) < (inputLen << 3))
			count[1]++;
		count[1] += (inputLen >>> 29);
		partLen = 64 - index;
		//Transform as many times as possible
		if(inputLen >= partLen){
			md5Memcpy(buffer, inbuf, index, 0, partLen);
			md5Transform(buffer);
			for(i=partLen; i+63<inputLen; i+=64){
				md5Memcpy(block, inbuf, 0, i, 64);
				md5Transform(block);
			}
			index = 0;
		}else
			i = 0;
		//Buffer remaining input
		md5Memcpy(buffer, inbuf, index, i, inputLen-i);
	}
	
	/**
	 * 整理和填写输出结果
	 * @see 将得到的128位(16字节)的MD5码存放在digest数组
	 */
	private void md5Final(){
		byte[] bits = new byte[8];
		int index, padLen;
		//Save number of bits
		Encode(bits, count, 8);
		//Pad out to 56 mod 64
		index = (int)(count[0]>>>3) & 0x3f;
		padLen = (index<56) ? (56-index) : (120-index);
		md5Update(PADDING, padLen);
		//Append length (before padding)
		md5Update(bits, 8);
		//Store state in digest
		Encode(digest, state, 16);
	}
	
	/**
	 * 这是一个内部使用的byte数组的块复制函数
	 * @see 从input的inpos开始把len长度的字节复制到output的outpos位置开始
	 */
	private void md5Memcpy(byte[] output, byte[] input, int outpos, int inpos, int len){
		int i;
		for(i=0; i<len; i++)
			output[outpos+i] = input[inpos+i];
	}
	
	/**
	 * 这是MD5核心变换程序。由md5Update调用
	 * @param block 分块的原始字节
	 */
	private void md5Transform(byte block[]){
		long a=state[0], b=state[1], c=state[2], d=state[3];
		long[] x = new long[16];
		Decode(x, block, 64);
		/*Round 1*/
		a = FF(a, b, c, d, x[0], S11, 0xd76aa478L);  // 1
		d = FF(d, a, b, c, x[1], S12, 0xe8c7b756L);  // 2
		c = FF(c, d, a, b, x[2], S13, 0x242070dbL);  // 3
		b = FF(b, c, d, a, x[3], S14, 0xc1bdceeeL);  // 4
		a = FF(a, b, c, d, x[4], S11, 0xf57c0fafL);  // 5
		d = FF(d, a, b, c, x[5], S12, 0x4787c62aL);  // 6
		c = FF(c, d, a, b, x[6], S13, 0xa8304613L);  // 7
		b = FF(b, c, d, a, x[7], S14, 0xfd469501L);  // 8
		a = FF(a, b, c, d, x[8], S11, 0x698098d8L);  // 9
		d = FF(d, a, b, c, x[9], S12, 0x8b44f7afL);  //10
		c = FF(c, d, a, b, x[10], S13, 0xffff5bb1L); //11
		b = FF(b, c, d, a, x[11], S14, 0x895cd7beL); //12
		a = FF(a, b, c, d, x[12], S11, 0x6b901122L); //13
		d = FF(d, a, b, c, x[13], S12, 0xfd987193L); //14
		c = FF(c, d, a, b, x[14], S13, 0xa679438eL); //15
		b = FF(b, c, d, a, x[15], S14, 0x49b40821L); //16
		/*Round 2*/
		a = GG(a, b, c, d, x[1], S21, 0xf61e2562L);  //17
		d = GG(d, a, b, c, x[6], S22, 0xc040b340L);  //18
		c = GG(c, d, a, b, x[11], S23, 0x265e5a51L); //19
		b = GG(b, c, d, a, x[0], S24, 0xe9b6c7aaL);  //20
		a = GG(a, b, c, d, x[5], S21, 0xd62f105dL);  //21
		d = GG(d, a, b, c, x[10], S22, 0x2441453L);  //22
		c = GG(c, d, a, b, x[15], S23, 0xd8a1e681L); //23
		b = GG(b, c, d, a, x[4], S24, 0xe7d3fbc8L);  //24
		a = GG(a, b, c, d, x[9], S21, 0x21e1cde6L);  //25
		d = GG(d, a, b, c, x[14], S22, 0xc33707d6L); //26
		c = GG(c, d, a, b, x[3], S23, 0xf4d50d87L);  //27
		b = GG(b, c, d, a, x[8], S24, 0x455a14edL);  //28
		a = GG(a, b, c, d, x[13], S21, 0xa9e3e905L); //29
		d = GG(d, a, b, c, x[2], S22, 0xfcefa3f8L);  //30
		c = GG(c, d, a, b, x[7], S23, 0x676f02d9L);  //31
		b = GG(b, c, d, a, x[12], S24, 0x8d2a4c8aL); //32
		/*Round 3*/
		a = HH(a, b, c, d, x[5], S31, 0xfffa3942L);  //33
		d = HH(d, a, b, c, x[8], S32, 0x8771f681L);  //34
		c = HH(c, d, a, b, x[11], S33, 0x6d9d6122L); //35
		b = HH(b, c, d, a, x[14], S34, 0xfde5380cL); //36
		a = HH(a, b, c, d, x[1], S31, 0xa4beea44L);  //37
		d = HH(d, a, b, c, x[4], S32, 0x4bdecfa9L);  //38
		c = HH(c, d, a, b, x[7], S33, 0xf6bb4b60L);  //39
		b = HH(b, c, d, a, x[10], S34, 0xbebfbc70L); //40
		a = HH(a, b, c, d, x[13], S31, 0x289b7ec6L); //41
		d = HH(d, a, b, c, x[0], S32, 0xeaa127faL);  //42
		c = HH(c, d, a, b, x[3], S33, 0xd4ef3085L);  //43
		b = HH(b, c, d, a, x[6], S34, 0x4881d05L);   //44
		a = HH(a, b, c, d, x[9], S31, 0xd9d4d039L);  //45
		d = HH(d, a, b, c, x[12], S32, 0xe6db99e5L); //46
		c = HH(c, d, a, b, x[15], S33, 0x1fa27cf8L); //47
		b = HH(b, c, d, a, x[2], S34, 0xc4ac5665L);  //48
		/*Round 4*/
		a = II(a, b, c, d, x[0], S41, 0xf4292244L);  //49
		d = II(d, a, b, c, x[7], S42, 0x432aff97L);  //50
		c = II(c, d, a, b, x[14], S43, 0xab9423a7L); //51
		b = II(b, c, d, a, x[5], S44, 0xfc93a039L);  //52
		a = II(a, b, c, d, x[12], S41, 0x655b59c3L); //53
		d = II(d, a, b, c, x[3], S42, 0x8f0ccc92L);  //54
		c = II(c, d, a, b, x[10], S43, 0xfeff47dL);  //55
		b = II(b, c, d, a, x[1], S44, 0x85845dd1L);  //56
		a = II(a, b, c, d, x[8], S41, 0x6fa87e4fL);  //57
		d = II(d, a, b, c, x[15], S42, 0xfe2ce6e0L); //58
		c = II(c, d, a, b, x[6], S43, 0xa3014314L);  //59
		b = II(b, c, d, a, x[13], S44, 0x4e0811a1L); //60
		a = II(a, b, c, d, x[4], S41, 0xf7537e82L);  //61
		d = II(d, a, b, c, x[11], S42, 0xbd3af235L); //62
		c = II(c, d, a, b, x[2], S43, 0x2ad7d2bbL);  //63
		b = II(b, c, d, a, x[9], S44, 0xeb86d391L);  //64
		state[0] += a;
		state[1] += b;
		state[2] += c;
		state[3] += d;
	}
	
	/**
	 * 把long数组按顺序拆成byte数组
	 * @see 因为Java的long类型是64bit的，只拆低32bit，以适应原始C实现的用途
	 */
	private void Encode(byte[] output, long[] input, int len){
		int i, j;
		for(i=0,j=0; j<len; i++,j+=4){
			output[j] = (byte)(input[i] & 0xffL);
			output[j+1] = (byte)((input[i]>>>8) & 0xffL);
			output[j+2] = (byte)((input[i]>>>16) & 0xffL);
			output[j+3] = (byte)((input[i]>>>24) & 0xffL);
		}
	}
	
	/**
	 * 把byte数组按顺序合成long数组
	 * @see 因为Java的long类型是64bit的，只合成低32bit，高32bit清零，以适应原始C实现的用途
	 */
	private void Decode(long[] output, byte[] input, int len){
		int i, j;
		for(i=0,j=0; j<len; i++,j+=4)
			output[i] = b2iu(input[j]) | (b2iu(input[j+1])<<8) | (b2iu(input[j+2])<<16) | (b2iu(input[j+3])<<24);
		return;
	}
	
	/**
	 * 将一字节的有符号数转换成一无符号的long型值
	 * @see 该方法是一个把byte按照不考虑正负号的原则的"升位"程序
	 * @see 因为Java没有unsigned运算
	 */
	public static long b2iu(byte b){
		//或者写成return b >= 0 ? b : b & 0xff;
		return b<0 ? b&0x7F+128 : b;
	}
	
	/**
	 * 该方法用来把一个byte类型的数转换成十六进制的ASCII表示
	 * @see 因为Java中的byte的toString无法实现这一点
	 * @see 而我们又没有C语言中的sprintf(outbuf, "%02X", ib)
	 */
	public static String byteHEX(byte ib){
		char[] Digit = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};
		char[] ob = new char[2];
		ob[0] = Digit[(ib>>>4) & 0X0F];
		ob[1] = Digit[ib & 0X0F];
		String s = new String(ob);
		return s;
	}
	
	/**
	 * 对需要加密的字符串进行加密
	 * @see 即对字符串source进行MD5运算，返回该串的MD5字符串
	 */
	public static String toMD5(String source){
		MD5 md5 = new MD5();
		return md5.getMD5ofStr(source);
	}
	
	public static void main(String[] args) {
		System.out.println(toMD5("My name is Jadyer"));
	}
}