MD5算法详解 & 哈希长度拓展攻击
（未完成）
MD5算法
分组，填充
令原信息长度为M位，填充使之满足
(M + N) mod 512 = 448 (N为填充位)
这样就使得 (M+N) = k * 512 + 448 bit
(512 - 448) = 64 bit 作为文件末尾存储填充前信息长度（M）
处理算法
幻数：
标准幻数为：1
2
3
4A = 0x 01 23 45 67
B = 0x 89 AB CD EF
C = 0x FE DC BA 98
D = 0x 76 54 32 10
实际上在程序中每个两位值被作为一个整数处理，小端存储的情况下，应写为：
1 | A = 0x 67 45 23 01 |
四轮循环运算：循环的次数是分组的个数（N+1）
示例代码（JAVA实现）1
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274public class MD5 {
static final String hexs[]={"0","1","2","3","4","5","6","7","8","9","A","B","C","D","E","F"};
//标准的幻数
private static final long A=0x67452301L;
private static final long B=0xefcdab89L;
private static final long C=0x98badcfeL;
private static final long D=0x10325476L;
//下面这些S11-S44实际上是一个4*4的矩阵，在四轮循环运算中用到
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;
//java不支持无符号的基本数据（unsigned）
private long [] result={A,B,C,D};//存储hash结果，共4×32=128位，初始化值为（幻数的级联）
public static void main(String []args){
MD5 md=new MD5();
System.out.println("md5(abc)="+md.digest("abc"));
}
private String digest(String inputStr){
byte [] inputBytes=inputStr.getBytes();
int byteLen=inputBytes.length;//长度（字节）
int groupCount=0;//完整分组的个数
groupCount=byteLen/64;//每组512位（64字节）
long []groups=null;//每个小组(64字节)再细分后的16个小组(4字节)
//处理每一个完整 分组
for(int step=0;step<groupCount;step++){
groups=divGroup(inputBytes,step*64);
trans(groups);//处理分组，核心算法
}
//处理完整分组后的尾巴
int rest=byteLen%64;//512位分组后的余数
byte [] tempBytes=new byte[64];
if(rest<=56){
for(int i=0;i<rest;i++)
tempBytes[i]=inputBytes[byteLen-rest+i];
if(rest<56){
tempBytes[rest]=(byte)(1<<7);
for(int i=1;i<56-rest;i++)
tempBytes[rest+i]=0;
}
long len=(long)(byteLen<<3);
for(int i=0;i<8;i++){
tempBytes[56+i]=(byte)(len&0xFFL);
len=len>>8;
}
groups=divGroup(tempBytes,0);
trans(groups);//处理分组
}else{
for(int i=0;i<rest;i++)
tempBytes[i]=inputBytes[byteLen-rest+i];
tempBytes[rest]=(byte)(1<<7);
for(int i=rest+1;i<64;i++)
tempBytes[i]=0;
groups=divGroup(tempBytes,0);
trans(groups);//处理分组
for(int i=0;i<56;i++)
tempBytes[i]=0;
long len=(long)(byteLen<<3);
for(int i=0;i<8;i++){
tempBytes[56+i]=(byte)(len&0xFFL);
len=len>>8;
}
groups=divGroup(tempBytes,0);
trans(groups);//处理分组
}
//将Hash值转换成十六进制的字符串
String resStr="";
long temp=0;
for(int i=0;i<4;i++){
for(int j=0;j<4;j++){
temp=result[i]&0x0FL;
String a=hexs[(int)(temp)];
result[i]=result[i]>>4;
temp=result[i]&0x0FL;
resStr+=hexs[(int)(temp)]+a;
result[i]=result[i]>>4;
}
}
return resStr;
}
/**
* 从inputBytes的index开始取512位，作为新的分组
* 将每一个512位的分组再细分成16个小组，每个小组64位（8个字节）
* @param inputBytes
* @param index
* @return
*/
private static long[] divGroup(byte[] inputBytes,int index){
long [] temp=new long[16];
for(int i=0;i<16;i++){
temp[i]=b2iu(inputBytes[4*i+index])|
(b2iu(inputBytes[4*i+1+index]))<<8|
(b2iu(inputBytes[4*i+2+index]))<<16|
(b2iu(inputBytes[4*i+3+index]))<<24;
}
return temp;
}
/**
* 这时不存在符号位（符号位存储不再是代表正负），所以需要处理一下
* @param b
* @return
*/
public static long b2iu(byte b){
return b < 0 ? b & 0x7F + 128 : b;
}
/**
* 主要的操作，四轮循环
* @param groups[]--每一个分组512位（64字节）
*/
private void trans(long[] groups) {
long a = result[0], b = result[1], c = result[2], d = result[3];
/*第一轮*/
a = FF(a, b, c, d, groups[0], S11, 0xd76aa478L); /* 1 */
d = FF(d, a, b, c, groups[1], S12, 0xe8c7b756L); /* 2 */
c = FF(c, d, a, b, groups[2], S13, 0x242070dbL); /* 3 */
b = FF(b, c, d, a, groups[3], S14, 0xc1bdceeeL); /* 4 */
a = FF(a, b, c, d, groups[4], S11, 0xf57c0fafL); /* 5 */
d = FF(d, a, b, c, groups[5], S12, 0x4787c62aL); /* 6 */
c = FF(c, d, a, b, groups[6], S13, 0xa8304613L); /* 7 */
b = FF(b, c, d, a, groups[7], S14, 0xfd469501L); /* 8 */
a = FF(a, b, c, d, groups[8], S11, 0x698098d8L); /* 9 */
d = FF(d, a, b, c, groups[9], S12, 0x8b44f7afL); /* 10 */
c = FF(c, d, a, b, groups[10], S13, 0xffff5bb1L); /* 11 */
b = FF(b, c, d, a, groups[11], S14, 0x895cd7beL); /* 12 */
a = FF(a, b, c, d, groups[12], S11, 0x6b901122L); /* 13 */
d = FF(d, a, b, c, groups[13], S12, 0xfd987193L); /* 14 */
c = FF(c, d, a, b, groups[14], S13, 0xa679438eL); /* 15 */
b = FF(b, c, d, a, groups[15], S14, 0x49b40821L); /* 16 */
/*第二轮*/
a = GG(a, b, c, d, groups[1], S21, 0xf61e2562L); /* 17 */
d = GG(d, a, b, c, groups[6], S22, 0xc040b340L); /* 18 */
c = GG(c, d, a, b, groups[11], S23, 0x265e5a51L); /* 19 */
b = GG(b, c, d, a, groups[0], S24, 0xe9b6c7aaL); /* 20 */
a = GG(a, b, c, d, groups[5], S21, 0xd62f105dL); /* 21 */
d = GG(d, a, b, c, groups[10], S22, 0x2441453L); /* 22 */
c = GG(c, d, a, b, groups[15], S23, 0xd8a1e681L); /* 23 */
b = GG(b, c, d, a, groups[4], S24, 0xe7d3fbc8L); /* 24 */
a = GG(a, b, c, d, groups[9], S21, 0x21e1cde6L); /* 25 */
d = GG(d, a, b, c, groups[14], S22, 0xc33707d6L); /* 26 */
c = GG(c, d, a, b, groups[3], S23, 0xf4d50d87L); /* 27 */
b = GG(b, c, d, a, groups[8], S24, 0x455a14edL); /* 28 */
a = GG(a, b, c, d, groups[13], S21, 0xa9e3e905L); /* 29 */
d = GG(d, a, b, c, groups[2], S22, 0xfcefa3f8L); /* 30 */
c = GG(c, d, a, b, groups[7], S23, 0x676f02d9L); /* 31 */
b = GG(b, c, d, a, groups[12], S24, 0x8d2a4c8aL); /* 32 */
/*第三轮*/
a = HH(a, b, c, d, groups[5], S31, 0xfffa3942L); /* 33 */
d = HH(d, a, b, c, groups[8], S32, 0x8771f681L); /* 34 */
c = HH(c, d, a, b, groups[11], S33, 0x6d9d6122L); /* 35 */
b = HH(b, c, d, a, groups[14], S34, 0xfde5380cL); /* 36 */
a = HH(a, b, c, d, groups[1], S31, 0xa4beea44L); /* 37 */
d = HH(d, a, b, c, groups[4], S32, 0x4bdecfa9L); /* 38 */
c = HH(c, d, a, b, groups[7], S33, 0xf6bb4b60L); /* 39 */
b = HH(b, c, d, a, groups[10], S34, 0xbebfbc70L); /* 40 */
a = HH(a, b, c, d, groups[13], S31, 0x289b7ec6L); /* 41 */
d = HH(d, a, b, c, groups[0], S32, 0xeaa127faL); /* 42 */
c = HH(c, d, a, b, groups[3], S33, 0xd4ef3085L); /* 43 */
b = HH(b, c, d, a, groups[6], S34, 0x4881d05L); /* 44 */
a = HH(a, b, c, d, groups[9], S31, 0xd9d4d039L); /* 45 */
d = HH(d, a, b, c, groups[12], S32, 0xe6db99e5L); /* 46 */
c = HH(c, d, a, b, groups[15], S33, 0x1fa27cf8L); /* 47 */
b = HH(b, c, d, a, groups[2], S34, 0xc4ac5665L); /* 48 */
/*第四轮*/
a = II(a, b, c, d, groups[0], S41, 0xf4292244L); /* 49 */
d = II(d, a, b, c, groups[7], S42, 0x432aff97L); /* 50 */
c = II(c, d, a, b, groups[14], S43, 0xab9423a7L); /* 51 */
b = II(b, c, d, a, groups[5], S44, 0xfc93a039L); /* 52 */
a = II(a, b, c, d, groups[12], S41, 0x655b59c3L); /* 53 */
d = II(d, a, b, c, groups[3], S42, 0x8f0ccc92L); /* 54 */
c = II(c, d, a, b, groups[10], S43, 0xffeff47dL); /* 55 */
b = II(b, c, d, a, groups[1], S44, 0x85845dd1L); /* 56 */
a = II(a, b, c, d, groups[8], S41, 0x6fa87e4fL); /* 57 */
d = II(d, a, b, c, groups[15], S42, 0xfe2ce6e0L); /* 58 */
c = II(c, d, a, b, groups[6], S43, 0xa3014314L); /* 59 */
b = II(b, c, d, a, groups[13], S44, 0x4e0811a1L); /* 60 */
a = II(a, b, c, d, groups[4], S41, 0xf7537e82L); /* 61 */
d = II(d, a, b, c, groups[11], S42, 0xbd3af235L); /* 62 */
c = II(c, d, a, b, groups[2], S43, 0x2ad7d2bbL); /* 63 */
b = II(b, c, d, a, groups[9], S44, 0xeb86d391L); /* 64 */
/*加入到之前计算的结果当中*/
result[0] += a;
result[1] += b;
result[2] += c;
result[3] += d;
result[0]=result[0]&0xFFFFFFFFL;
result[1]=result[1]&0xFFFFFFFFL;
result[2]=result[2]&0xFFFFFFFFL;
result[3]=result[3]&0xFFFFFFFFL;
}
/**
* 下面是处理要用到的线性函数
*/
private static long F(long x, long y, long z) {
return (x & y) | ((~x) & z);
}
private static long G(long x, long y, long z) {
return (x & z) | (y & (~z));
}
private static long H(long x, long y, long z) {
return x ^ y ^ z;
}
private static long I(long x, long y, long z) {
return y ^ (x | (~z));
}
private static long FF(long a, long b, long c, long d, long x, long s,
long ac) {
a += (F(b, c, d)&0xFFFFFFFFL) + x + ac;
a = ((a&0xFFFFFFFFL)<< s) | ((a&0xFFFFFFFFL) >>> (32 - s));
a += b;
return (a&0xFFFFFFFFL);
}
private static long GG(long a, long b, long c, long d, long x, long s,
long ac) {
a += (G(b, c, d)&0xFFFFFFFFL) + x + ac;
a = ((a&0xFFFFFFFFL) << s) | ((a&0xFFFFFFFFL) >>> (32 - s));
a += b;
return (a&0xFFFFFFFFL);
}
private static long HH(long a, long b, long c, long d, long x, long s,
long ac) {
a += (H(b, c, d)&0xFFFFFFFFL) + x + ac;
a = ((a&0xFFFFFFFFL) << s) | ((a&0xFFFFFFFFL) >>> (32 - s));
a += b;
return (a&0xFFFFFFFFL);
}
private static long II(long a, long b, long c, long d, long x, long s,
long ac) {
a += (I(b, c, d)&0xFFFFFFFFL) + x + ac;
a = ((a&0xFFFFFFFFL) << s) | ((a&0xFFFFFFFFL) >>> (32 - s));
a += b;
return (a&0xFFFFFFFFL);
}
}