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本文詳細講解視頻如下：
《C語言實現(xiàn)MD5算法》
摘要算法又稱哈希算法。
它表示輸入任意長度的數(shù)據(jù)，輸出固定長度的數(shù)據(jù)，它的主要特征是加密過程不需要密鑰，并且經(jīng)過加密的數(shù)據(jù)無法被解密。
目前可以被解密逆向的只有CRC32算法，只有輸入相同的明文數(shù)據(jù)經(jīng)過相同的消息摘要算法才能得到相同的密文。
消息摘要算法不存在密鑰的管理與分發(fā)問題，適合于分布式網(wǎng)絡(luò)上使用。由于其加密計算的工作量相當巨大，所以以前的這種算法通常只用于數(shù)據(jù)量有限的情況下的加密。
這三類算法的主要作用：驗證數(shù)據(jù)的完整性
MD5即Message-Digest Algorithm 5（信息-摘要算法）。
屬于摘要算法，是一個不可逆過程，就是無論多大數(shù)據(jù)，經(jīng)過算法運算后都是生成固定長度的數(shù)據(jù)，結(jié)果使用16進制進行顯示的128bit的二進制串。通常表示為32個十六進制數(shù)連成的字符串。
MD5有什么用？
用于確保信息傳輸完整一致。是計算機廣泛使用的雜湊算法之一（又譯摘要算法、哈希算法），主流編程語言普遍已有MD5實現(xiàn)。更多用在文檔校驗上，用來生成密鑰檢測文檔是否被篡改。
有很多在線進行MD5加密的網(wǎng)站，如下：
http://www.metools.info/code/c26.html
舉例: 給字符串 12334567 加密成。
如圖結(jié)果為：
32135A337F8DC8E2BB9A9B80D86BDFD0
源文件如下：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
md5.c
include
include &34;md5.h&34;
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 = 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,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);
FF(d, a, b, c, x[ 1], 12, 0xe8c7b756);
FF(c, d, a, b, x[ 2], 17, 0x242070db);
FF(b, c, d, a, x[ 3], 22, 0xc1bdceee);
FF(a, b, c, d, x[ 4], 7, 0xf57c0faf);
FF(d, a, b, c, x[ 5], 12, 0x4787c62a);
FF(c, d, a, b, x[ 6], 17, 0xa8304613);
FF(b, c, d, a, x[ 7], 22, 0xfd469501);
FF(a, b, c, d, x[ 8], 7, 0x698098d8);
FF(d, a, b, c, x[ 9], 12, 0x8b44f7af);
FF(c, d, a, b, x[10], 17, 0xffff5bb1);
FF(b, c, d, a, x[11], 22, 0x895cd7be);
FF(a, b, c, d, x[12], 7, 0x6b901122);
FF(d, a, b, c, x[13], 12, 0xfd987193);
FF(c, d, a, b, x[14], 17, 0xa679438e);
FF(b, c, d, a, x[15], 22, 0x49b40821);
GG(a, b, c, d, x[ 1], 5, 0xf61e2562);
GG(d, a, b, c, x[ 6], 9, 0xc040b340);
GG(c, d, a, b, x[11], 14, 0x265e5a51);
GG(b, c, d, a, x[ 0], 20, 0xe9b6c7aa);
GG(a, b, c, d, x[ 5], 5, 0xd62f105d);
GG(d, a, b, c, x[10], 9, 0x2441453);
GG(c, d, a, b, x[15], 14, 0xd8a1e681);
GG(b, c, d, a, x[ 4], 20, 0xe7d3fbc8);
GG(a, b, c, d, x[ 9], 5, 0x21e1cde6);
GG(d, a, b, c, x[14], 9, 0xc33707d6);
GG(c, d, a, b, x[ 3], 14, 0xf4d50d87);
GG(b, c, d, a, x[ 8], 20, 0x455a14ed);
GG(a, b, c, d, x[13], 5, 0xa9e3e905);
GG(d, a, b, c, x[ 2], 9, 0xfcefa3f8);
GG(c, d, a, b, x[ 7], 14, 0x676f02d9);
GG(b, c, d, a, x[12], 20, 0x8d2a4c8a);
HH(a, b, c, d, x[ 5], 4, 0xfffa3942);
HH(d, a, b, c, x[ 8], 11, 0x8771f681);
HH(c, d, a, b, x[11], 16, 0x6d9d6122);
HH(b, c, d, a, x[14], 23, 0xfde5380c);
HH(a, b, c, d, x[ 1], 4, 0xa4beea44);
HH(d, a, b, c, x[ 4], 11, 0x4bdecfa9);
HH(c, d, a, b, x[ 7], 16, 0xf6bb4b60);
HH(b, c, d, a, x[10], 23, 0xbebfbc70);
HH(a, b, c, d, x[13], 4, 0x289b7ec6);
HH(d, a, b, c, x[ 0], 11, 0xeaa127fa);
HH(c, d, a, b, x[ 3], 16, 0xd4ef3085);
HH(b, c, d, a, x[ 6], 23, 0x4881d05);
HH(a, b, c, d, x[ 9], 4, 0xd9d4d039);
HH(d, a, b, c, x[12], 11, 0xe6db99e5);
HH(c, d, a, b, x[15], 16, 0x1fa27cf8);
HH(b, c, d, a, x[ 2], 23, 0xc4ac5665);
II(a, b, c, d, x[ 0], 6, 0xf4292244);
II(d, a, b, c, x[ 7], 10, 0x432aff97);
II(c, d, a, b, x[14], 15, 0xab9423a7);
II(b, c, d, a, x[ 5], 21, 0xfc93a039);
II(a, b, c, d, x[12], 6, 0x655b59c3);
II(d, a, b, c, x[ 3], 10, 0x8f0ccc92);
II(c, d, a, b, x[10], 15, 0xffeff47d);
II(b, c, d, a, x[ 1], 21, 0x85845dd1);
II(a, b, c, d, x[ 8], 6, 0x6fa87e4f);
II(d, a, b, c, x[15], 10, 0xfe2ce6e0);
II(c, d, a, b, x[ 6], 15, 0xa3014314);
II(b, c, d, a, x[13], 21, 0x4e0811a1);
II(a, b, c, d, x[ 4], 6, 0xf7537e82);
II(d, a, b, c, x[11], 10, 0xbd3af235);
II(c, d, a, b, x[ 2], 15, 0x2ad7d2bb);
II(b, c, d, a, x[ 9], 21, 0xeb86d391);
state[0] += a;
state[1] += b;
state[2] += c;
state[3] += d;
}
MD5加密步驟如下：
MD5_CTX md5c;
MD5Init(MD5_CTX *context);
實現(xiàn)MD5值的計算及結(jié)構(gòu)體的更新：
MD5Update(MD5_CTX *context,(unsigned char *)input,inputLen);
MD5Final(MD5_CTX *context,unsigned char digest[16]);
轉(zhuǎn)換成32位的16進制字符串。
對字符串進行加密：
1 include
2 include
3 include &34;md5.h&34;
4 include
5 include
6 include
7 include
8
9 void main( void )
10 {
11 int read_len;
12 int i ;
13 char temp[8]={0};
14 unsigned char digest[16]; //存放結(jié)果
15 char hexbuf[128]=&34;12334567&34;;
16 unsigned char decrypt[16]={0};
17 unsigned char decrypt32[64]={0};
18
19 MD5_CTX md5c;
20
21 MD5Init(&md5c); //初始化
22 read_len = strlen(hexbuf);
23 MD5Update(&md5c,(unsigned char *)hexbuf,read_len);
24
25 MD5Final(&md5c,decrypt);
26 strcpy((char *)decrypt32,&34;&34;);
27
28 for(i=0;i<16;i++)
29 {
30 sprintf(temp,&34;%02x&34;,decrypt[i]);
31 strcat((char *)decrypt32,temp);
32 }
33 printf(&34;md5:%sn&34;,decrypt32);
34
35 return;
36 }
執(zhí)行結(jié)果如下：
本例對字符串12334567進行加密，結(jié)果和在線加密結(jié)果一致。
對文件進行加密
include
include
include &34;md5.h&34;
include
include
include
include
define FORWORD_FW &34;123.c&34;
int calc_md5(char*filename,char*dest)
{
int i;
int filelen = 0;
int read_len;
char temp[8]={0};
char hexbuf[128]={0};
unsigned char decrypt[16]={0};
unsigned char decrypt32[64]={0};
MD5_CTX md5;
char fw_path[128];
int fdf;
fdf = open(filename,O_RDWR);
if(fdf<0)
{
printf(&34;%s not existn&34;,FORWORD_FW);
return -1;
}
MD5Init(&md5);
while(1)
{
read_len = read(fdf, hexbuf,sizeof(hexbuf));
if (read_len <0) {
close(fdf);
return -1;
}
if(read_len==0)
{
break;
}
filelen += read_len;
MD5Update(&md5,(unsigned char *)hexbuf,read_len);
}
MD5Final(&md5,decrypt);
strcpy((char *)decrypt32,&34;&34;);
for(i=0;i<16;i++)
{
sprintf(temp,&34;%02x&34;,decrypt[i]);
strcat((char *)decrypt32,temp);
}
strcpy(dest,decrypt32);
printf(&34;md5:%s len=%dn&34;,dest,filelen);
close(fdf);
return filelen;
}
int main(int argc, char *argv[])
{
int ret;
int filelen;
char md5_str[64]={0};
char cmd[256]={0};
filelen = calc_md5(FORWORD_FW,md5_str);
if(filelen<0)
{
printf(&34;calc_md5 failn&34;);
return -1;
}
return 0;
}
運行結(jié)果：
在線驗證結(jié)果對比：
http://www.metools.info/other/o21.html
結(jié)果
丁楠明