题中所示代码中，python实现了计算空字符串的MD5值，并对MD5的值的十六进制的字符串所表示的字节进行BASE64处理。
不像Python内部有实现md5功能，根据ANSI C标准，C语言的标准库里是没有md5功能的；
但是RFC1231规定了MD5功能的C实现并提供了附件，可以直接用，也可以直接获取现成的实现，在编译链接时指定正确的.h头文件和.lib静态链接库文件；
这里我采取前者的做法（电脑上没有装VC，有VC就简单很多，使用的是minGW）大概六七百行代码左右。
然后这里展示不完，给个实现效果图
这是我整理的实现代码，其中BASE64部分使用了github上littlestar的b64.c，然后MD5计算部分直接参考了RFC1231标准的附录。RFC1231文件有计算方法
BASE64的编码原理
#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
源文件md5.c
#include <memory.h>
#include "md5.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,index = 0,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 = partleni+64 <= inputleni+=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,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,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 */
