算法 MD5

头文件定义（MD5.h）：

#ifndef MD5_H
#define MD5_H
 
 
typedef struct
{
  unsigned int count[2];
  unsigned int state[4];
  unsigned char buffer[64];
} MD5_CTX;
 
#define F(x,y,z) ((x & y) | (~x & z))
#define G(x,y,z) ((x & z) | (y & ~z))
#define H(x,y,z) (x^y^z)
#define I(x,y,z) (y ^ (x | ~z))
#define ROTATE_LEFT(x,n) ((x << n) | (x >> (32-n)))
 
#define FF(a,b,c,d,x,s,ac) \
{ \
  a += F(b,c,d) + x + ac; \
  a = ROTATE_LEFT(a,s); \
  a += b; \
}
#define GG(a,b,c,d,x,s,ac) \
{ \
  a += G(b,c,d) + x + ac; \
  a = ROTATE_LEFT(a,s); \
  a += b; \
}
#define HH(a,b,c,d,x,s,ac) \
{ \
  a += H(b,c,d) + x + ac; \
  a = ROTATE_LEFT(a,s); \
  a += b; \
}
#define II(a,b,c,d,x,s,ac) \
{ \
  a += I(b,c,d) + x + ac; \
  a = ROTATE_LEFT(a,s); \
  a += b; \
}
void MD5Init(MD5_CTX *context);
void MD5Update(MD5_CTX *context, unsigned char *input, unsigned int inputlen);
void MD5Final(MD5_CTX *context, unsigned char digest[16]);
void MD5Transform(unsigned int state[4], unsigned char block[64]);
void MD5Encode(unsigned char *output, unsigned int *input, unsigned int len);
void MD5Decode(unsigned int *output, unsigned char *input, unsigned int len);
 
#endif

源码实现（MD5.cpp）：

#include "stdafx.h"
#include "md5.h"
#include <memory.h>
#include <stdlib.h>
#include <stdio.h>
#include<fcntl.h>
unsigned char PADDING[] =
{
  0x80,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
  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
};
 
void MD5Init(MD5_CTX *context)
{
  context->count[0] = 0;
  context->count[1] = 0;
  context->state[0] = 0x67452301;
  context->state[1] = 0xEFCDAB89;
  context->state[2] = 0x98BADCFE;
  context->state[3] = 0x10325476;
}
 
void MD5Update(MD5_CTX *context, unsigned char *input, unsigned int inputlen)
{
  unsigned int i = 0;
  unsigned int index = 0;
  unsigned int partlen = 0;
 
  index = (context->count[0] >> 3) & 0x3F;
  partlen = 64 - index;
  context->count[0] += inputlen << 3;
 
  if(context->count[0] < (inputlen << 3))
    context->count[1]++;
  context->count[1] += inputlen >> 29;
 
  if(inputlen >= partlen)
  {
    memcpy(&context->buffer[index], input,partlen);
    MD5Transform(context->state, context->buffer);
 
    for(i = partlen; i+64 <= inputlen; i+=64)
      MD5Transform(context->state, &input[i]);
 
    index = 0;
  }
  else
  {
    i = 0;
  }
  memcpy(&context->buffer[index], &input[i], inputlen-i);
}
 
void MD5Final(MD5_CTX *context, unsigned char digest[16])
{
  unsigned int index = 0,padlen = 0;
  unsigned char bits[8];
 
  index = (context->count[0] >> 3) & 0x3F;
  padlen = (index < 56)?(56-index):(120-index);
  MD5Encode(bits, context->count, 8);
  MD5Update(context, PADDING, padlen);
  MD5Update(context, bits, 8);
  MD5Encode(digest, context->state, 16);
}
 
void MD5Encode(unsigned char *output,unsigned int *input,unsigned int len)
{
  unsigned int i = 0;
  unsigned int j = 0;
 
  while(j < len)
  {
    output[j] = input[i] & 0xFF;
    output[j+1] = (input[i] >> 8) & 0xFF;
    output[j+2] = (input[i] >> 16) & 0xFF;
    output[j+3] = (input[i] >> 24) & 0xFF;
    i++;
    j += 4;
  }
}
 
void MD5Decode(unsigned int *output, unsigned char *input, unsigned int len)
{
  unsigned int i = 0;
  unsigned int j = 0;
 
  while(j < len)
  {
    output[i] = (input[j]) |
      (input[j+1] << 8) |
      (input[j+2] << 16) |
      (input[j+3] << 24);
    i++;
    j += 4;
  }
}
 
void MD5Transform(unsigned int state[4], unsigned char block[64])
{
  unsigned int a = state[0];
  unsigned int b = state[1];
  unsigned int c = state[2];
  unsigned int d = state[3];
  unsigned int x[64];
 
  MD5Decode(x,block,64);
 
  FF(a, b, c, d, x[ 0], 7, 0xd76aa478); /* 1 */
  FF(d, a, b, c, x[ 1], 12, 0xe8c7b756); /* 2 */
  FF(c, d, a, b, x[ 2], 17, 0x242070db); /* 3 */
  FF(b, c, d, a, x[ 3], 22, 0xc1bdceee); /* 4 */
  FF(a, b, c, d, x[ 4], 7, 0xf57c0faf); /* 5 */
  FF(d, a, b, c, x[ 5], 12, 0x4787c62a); /* 6 */
  FF(c, d, a, b, x[ 6], 17, 0xa8304613); /* 7 */
  FF(b, c, d, a, x[ 7], 22, 0xfd469501); /* 8 */
  FF(a, b, c, d, x[ 8], 7, 0x698098d8); /* 9 */
  FF(d, a, b, c, x[ 9], 12, 0x8b44f7af); /* 10 */
  FF(c, d, a, b, x[10], 17, 0xffff5bb1); /* 11 */
  FF(b, c, d, a, x[11], 22, 0x895cd7be); /* 12 */
  FF(a, b, c, d, x[12], 7, 0x6b901122); /* 13 */
  FF(d, a, b, c, x[13], 12, 0xfd987193); /* 14 */
  FF(c, d, a, b, x[14], 17, 0xa679438e); /* 15 */
  FF(b, c, d, a, x[15], 22, 0x49b40821); /* 16 */
 
  /* Round 2 */
  GG(a, b, c, d, x[ 1], 5, 0xf61e2562); /* 17 */
  GG(d, a, b, c, x[ 6], 9, 0xc040b340); /* 18 */
  GG(c, d, a, b, x[11], 14, 0x265e5a51); /* 19 */
  GG(b, c, d, a, x[ 0], 20, 0xe9b6c7aa); /* 20 */
  GG(a, b, c, d, x[ 5], 5, 0xd62f105d); /* 21 */
  GG(d, a, b, c, x[10], 9,  0x2441453); /* 22 */
  GG(c, d, a, b, x[15], 14, 0xd8a1e681); /* 23 */
  GG(b, c, d, a, x[ 4], 20, 0xe7d3fbc8); /* 24 */
  GG(a, b, c, d, x[ 9], 5, 0x21e1cde6); /* 25 */
  GG(d, a, b, c, x[14], 9, 0xc33707d6); /* 26 */
  GG(c, d, a, b, x[ 3], 14, 0xf4d50d87); /* 27 */
  GG(b, c, d, a, x[ 8], 20, 0x455a14ed); /* 28 */
  GG(a, b, c, d, x[13], 5, 0xa9e3e905); /* 29 */
  GG(d, a, b, c, x[ 2], 9, 0xfcefa3f8); /* 30 */
  GG(c, d, a, b, x[ 7], 14, 0x676f02d9); /* 31 */
  GG(b, c, d, a, x[12], 20, 0x8d2a4c8a); /* 32 */
 
  /* Round 3 */
  HH(a, b, c, d, x[ 5], 4, 0xfffa3942); /* 33 */
  HH(d, a, b, c, x[ 8], 11, 0x8771f681); /* 34 */
  HH(c, d, a, b, x[11], 16, 0x6d9d6122); /* 35 */
  HH(b, c, d, a, x[14], 23, 0xfde5380c); /* 36 */
  HH(a, b, c, d, x[ 1], 4, 0xa4beea44); /* 37 */
  HH(d, a, b, c, x[ 4], 11, 0x4bdecfa9); /* 38 */
  HH(c, d, a, b, x[ 7], 16, 0xf6bb4b60); /* 39 */
  HH(b, c, d, a, x[10], 23, 0xbebfbc70); /* 40 */
  HH(a, b, c, d, x[13], 4, 0x289b7ec6); /* 41 */
  HH(d, a, b, c, x[ 0], 11, 0xeaa127fa); /* 42 */
  HH(c, d, a, b, x[ 3], 16, 0xd4ef3085); /* 43 */
  HH(b, c, d, a, x[ 6], 23,  0x4881d05); /* 44 */
  HH(a, b, c, d, x[ 9], 4, 0xd9d4d039); /* 45 */
  HH(d, a, b, c, x[12], 11, 0xe6db99e5); /* 46 */
  HH(c, d, a, b, x[15], 16, 0x1fa27cf8); /* 47 */
  HH(b, c, d, a, x[ 2], 23, 0xc4ac5665); /* 48 */
 
  /* Round 4 */
  II(a, b, c, d, x[ 0], 6, 0xf4292244); /* 49 */
  II(d, a, b, c, x[ 7], 10, 0x432aff97); /* 50 */
  II(c, d, a, b, x[14], 15, 0xab9423a7); /* 51 */
  II(b, c, d, a, x[ 5], 21, 0xfc93a039); /* 52 */
  II(a, b, c, d, x[12], 6, 0x655b59c3); /* 53 */
  II(d, a, b, c, x[ 3], 10, 0x8f0ccc92); /* 54 */
  II(c, d, a, b, x[10], 15, 0xffeff47d); /* 55 */
  II(b, c, d, a, x[ 1], 21, 0x85845dd1); /* 56 */
  II(a, b, c, d, x[ 8], 6, 0x6fa87e4f); /* 57 */
  II(d, a, b, c, x[15], 10, 0xfe2ce6e0); /* 58 */
  II(c, d, a, b, x[ 6], 15, 0xa3014314); /* 59 */
  II(b, c, d, a, x[13], 21, 0x4e0811a1); /* 60 */
  II(a, b, c, d, x[ 4], 6, 0xf7537e82); /* 61 */
  II(d, a, b, c, x[11], 10, 0xbd3af235); /* 62 */
  II(c, d, a, b, x[ 2], 15, 0x2ad7d2bb); /* 63 */
  II(b, c, d, a, x[ 9], 21, 0xeb86d391); /* 64 */
  state[0] += a;
  state[1] += b;
  state[2] += c;
  state[3] += d;
}