Md5是计算机广泛使用的,用于确保信息传输完整一致的杂凑算法。它的基础原理是:将数据(如汉字)运算为另一固定长度值。MD5的前身有MD2、MD3和MD4
1、压缩性:任意长度的数据,算出的MD5值长度都是固定的。
2、容易计算:从原数据计算出MD5值很容易。
3、抗修改性:对原数据进行任何改动,哪怕只修改1个字节,所得到的MD5值都有很大区别。
4、强抗碰撞:已知原数据和其MD5值,想找到一个具有相同MD5值的数据(即伪造数据)是非常困难的。
1、各种安全访问的认证
2、数据一致性验证
3、数字签名
在MD5算法中,首先需要对信息进行填充,使其位长对512求余的结果等于448,并且填充必须进行,即使其位长对512求余的结果等于448。(原因是为满足后面处理中对信息长度的要求)因此,信息的位长(Bits Length)将被扩展至N*512+448,N为一个非负整数,N可以是零。
填充的方法:在信息的后面填充一个1和无数个0,直到满足上面的条件时才停止用0对信息的填充。
在这个结果后面附加一个以64位二进制表示的填充前信息长度,如果二进制表示的填充前信息长度超过64位,则取低64位。
数据的长度=N*512+448+64=(N+1)*512,即长度恰好是512的整数倍。
初始的128位值为初试链接变量,这些参数用于第一轮的运算,以大端字节序来表示,他们分别为: A=0x01234567,B=0x89ABCDEF,C=0xFEDCBA98,D=0x76543210。
每一个变量给出的数值是按大端字节序存储的(即高字节存于内存低地址,低字节存于内存高地址)。故,在程序中变量A、B、C、D的值分别为0x67452301,0xEFCDAB89,0x98BADCFE,0x10325476
需要进行四次循环运算,循环次数是分组个数的N+1
运算所需的四个函数(&是与(And),|是或(Or),~是非(Not),^是异或(Xor)):
F( X ,Y ,Z ) = (X & Y ) | ( (~X) & Z )
G( X ,Y ,Z ) = (X & Z ) | ( Y & (~Z) )
H( X ,Y ,Z ) =X^ Y ^ Z
I( X ,Y ,Z ) =Y^ ( X | (~Z) )
如果X、Y和Z的对应位是独立和均匀的,那么结果的每一位也应是独立和均匀的。
F是一个逐位运算的函数。即,如果X,那么Y,否则Z。函数H是逐位奇偶操作符。
具体算法流程如下:
(1)将每512字节分成16组,每组八个字节。
(2)假设Mj表示消息的第j个子分组(从0到15),常数ti是4294967296*abs( sin(i) )的整数部分,i取值从1到64,单位是弧度。(4294967296=232)
现定义:
FF(a ,b ,c ,d,Mj ,s ,ti )操作为 a = b + ( (a + F(b,c,d) + Mj + ti) <<
GG(a ,b ,c ,d,Mj ,s ,ti )操作为 a = b + ( (a + G(b,c,d) + Mj + ti) <<
HH(a ,b ,c ,d,Mj ,s ,ti)操作为 a = b + ( (a + H(b,c,d) + Mj + ti)<<< s)
II(a ,b ,c ,d,Mj ,s ,ti)操作为 a = b + ( (a + I(b,c,d) + Mj + ti)<<
注意:“<<<”表示循环左移位
这四轮(共64步)是:
第一轮
FF(a ,b ,c ,d,M0 ,7 ,0xd76aa478 )
FF(d ,a ,b ,c,M1 ,12 ,0xe8c7b756 )
FF(c ,d ,a ,b,M2 ,17 ,0x242070db )
FF(b ,c ,d ,a,M3 ,22 ,0xc1bdceee )
FF(a ,b ,c ,d,M4 ,7 ,0xf57c0faf )
FF(d ,a ,b ,c,M5 ,12 ,0x4787c62a )
FF(c ,d ,a ,b,M6 ,17 ,0xa8304613 )
FF(b ,c ,d ,a,M7 ,22 ,0xfd469501)
FF(a ,b ,c ,d,M8 ,7 ,0x698098d8 )
FF(d ,a ,b ,c,M9 ,12 ,0x8b44f7af )
FF(c ,d ,a ,b,M10 ,17 ,0xffff5bb1 )
FF(b ,c ,d ,a,M11 ,22 ,0x895cd7be )
FF(a ,b ,c ,d,M12 ,7 ,0x6b901122 )
FF(d ,a ,b ,c,M13 ,12 ,0xfd987193 )
FF(c ,d ,a ,b,M14 ,17 ,0xa679438e )
FF(b ,c ,d ,a,M15 ,22 ,0x49b40821 )
第二轮
GG(a ,b ,c ,d,M1 ,5 ,0xf61e2562 )
GG(d ,a ,b ,c,M6 ,9 ,0xc040b340 )
GG(c ,d ,a ,b,M11 ,14 ,0x265e5a51 )
GG(b ,c ,d ,a,M0 ,20 ,0xe9b6c7aa )
GG(a ,b ,c ,d,M5 ,5 ,0xd62f105d )
GG(d ,a ,b ,c,M10 ,9 ,0x02441453 )
GG(c ,d ,a ,b,M15 ,14 ,0xd8a1e681 )
GG(b ,c ,d ,a,M4 ,20 ,0xe7d3fbc8 )
GG(a ,b ,c ,d,M9 ,5 ,0x21e1cde6 )
GG(d ,a ,b ,c,M14 ,9 ,0xc33707d6 )
GG(c ,d ,a ,b,M3 ,14 ,0xf4d50d87 )
GG(b ,c ,d ,a,M8 ,20 ,0x455a14ed )
GG(a ,b ,c ,d,M13 ,5 ,0xa9e3e905 )
GG(d ,a ,b ,c,M2 ,9 ,0xfcefa3f8 )
GG(c ,d ,a ,b,M7 ,14 ,0x676f02d9 )
GG(b ,c ,d ,a,M12 ,20 ,0x8d2a4c8a )
第三轮
HH(a ,b ,c ,d,M5 ,4 ,0xfffa3942 )
HH(d ,a ,b ,c,M8 ,11 ,0x8771f681 )
HH(c ,d ,a ,b,M11 ,16 ,0x6d9d6122 )
HH(b ,c ,d ,a,M14 ,23 ,0xfde5380c )
HH(a ,b ,c ,d,M1 ,4 ,0xa4beea44 )
HH(d ,a ,b ,c,M4 ,11 ,0x4bdecfa9 )
HH(c ,d ,a ,b,M7 ,16 ,0xf6bb4b60 )
HH(b ,c ,d ,a,M10 ,23 ,0xbebfbc70 )
HH(a ,b ,c ,d,M13 ,4 ,0x289b7ec6 )
HH(d ,a ,b ,c,M0 ,11 ,0xeaa127fa )
HH(c ,d ,a ,b,M3 ,16 ,0xd4ef3085 )
HH(b ,c ,d ,a,M6 ,23 ,0x04881d05 )
HH(a ,b ,c ,d,M9 ,4 ,0xd9d4d039 )
HH(d ,a ,b ,c,M12 ,11 ,0xe6db99e5 )
HH(c ,d ,a ,b,M15 ,16 ,0x1fa27cf8 )
HH(b ,c ,d ,a,M2 ,23 ,0xc4ac5665 )
第四轮
II(a ,b ,c ,d,M0 ,6 ,0xf4292244 )
II(d ,a ,b ,c,M7 ,10 ,0x432aff97 )
II(c ,d ,a ,b,M14 ,15 ,0xab9423a7 )
II(b ,c ,d ,a,M5 ,21 ,0xfc93a039 )
II(a ,b ,c ,d,M12 ,6 ,0x655b59c3 )
II(d ,a ,b ,c,M3 ,10 ,0x8f0ccc92 )
II(c ,d ,a ,b,M10 ,15 ,0xffeff47d )
II(b ,c ,d ,a,M1 ,21 ,0x85845dd1 )
II(a ,b ,c ,d,M8 ,6 ,0x6fa87e4f )
II(d ,a ,b ,c,M15 ,10 ,0xfe2ce6e0 )
II(c ,d ,a ,b,M6 ,15 ,0xa3014314 )
II(b ,c ,d ,a,M13 ,21 ,0x4e0811a1 )
II(a ,b ,c ,d,M4 ,6 ,0xf7537e82 )
II(d ,a ,b ,c,M11 ,10 ,0xbd3af235 )
II(c ,d ,a ,b,M2 ,15 ,0x2ad7d2bb )
II(b ,c ,d ,a,M9 ,21 ,0xeb86d391 )
所有这些完成之后,将a、b、c、d分别在原来基础上再加上A、B、C、D。
即a = a + A,b = b + B,c = c + C,d = d + D
然后用下一分组数据继续运行以上算法。
最后的输出是a、b、c和d的级联。
当你按照我上面所说的方法实现MD5算法以后,你可以用以下几个信息对你做出来的程序作一个简单的测试,看看程序有没有错误。
MD5("a") = 0cc175b9c0f1b6a831c399e269772661
MD5("abc") = 900150983cd24fb0d6963f7d28e17f72
MD5("abcdefghijklmnopqrstuvwxyz") = c3fcd3d76192e4007dfb496cca67e13
MD5.c
#include
#include
#include
#include
#include
#define S11 7
#define S12 12
#define S13 17
#define S14 22
#define S21 5
#define S22 9
#define S23 14
#define S24 20
#define S31 4
#define S32 11
#define S33 16
#define S34 23
#define S41 6
#define S42 10
#define S43 15
#define S44 21
typedef struct {
unsigned int state[4];
unsigned int count[2];
unsigned char buffer[64];
} MD5Context;
static unsigned char PADDING[64] =
{
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
};
#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) + (unsigned int)(ac); \
(a) = ROTATE_LEFT((a), (s)); \
(a) += (b); \
}
#define GG(a, b, c, d, x, s, ac) \
{ \
(a) += G((b), (c), (d)) + (x) + (unsigned int)(ac); \
(a) = ROTATE_LEFT((a), (s)); \
(a) += (b); \
}
#define HH(a, b, c, d, x, s, ac) \
{ \
(a) += H((b), (c), (d)) + (x) + (unsigned int)(ac); \
(a) = ROTATE_LEFT((a), (s)); \
(a) += (b); \
}
#define II(a, b, c, d, x, s, ac) \
{ \
(a) += I((b), (c), (d)) + (x) + (unsigned int)(ac); \
(a) = ROTATE_LEFT((a), (s)); \
(a) += (b); \
}
static void MD5_Encode(unsigned char *output, unsigned int * input, int len)
{
unsigned int i, j;
for (i = 0, j = 0; j < len; i++, j += 4)
{
output[j] = (unsigned char) (input[i] & 0xff);
output[j + 1] = (unsigned char) ((input[i] >> 8) & 0xff);
output[j + 2] = (unsigned char) ((input[i] >> 16) & 0xff);
output[j + 3] = (unsigned char) ((input[i] >> 24) & 0xff);
}
}
static void MD5_Decode(unsigned int *output, unsigned char * input, int len)
{
unsigned int i, j;
for (i = 0, j = 0; j < len; i++, j += 4)
{
output[i] = ((unsigned int) input[j]) |
(((unsigned int) input[j + 1]) << 8) |
(((unsigned int) input[j + 2]) <<16) |
(((unsigned int) input[j + 3]) << 24);
}
}
static void MD5_Transform(unsigned intstate[4], unsigned char block[64])
{
unsigned int a = state[0], b = state[1], c = state[2], d = state[3], x[16];
MD5_Decode(x, block, 64);
/* Round 1 */
FF(a, b, c, d, x[0], S11, 0xd76aa478); /* 1 */
FF(d, a, b, c, x[1], S12, 0xe8c7b756); /* 2 */
FF(c, d, a, b, x[2], S13, 0x242070db); /* 3 */
FF(b, c, d, a, x[3], S14, 0xc1bdceee); /* 4 */
FF(a, b, c, d, x[4], S11, 0xf57c0faf); /* 5 */
FF(d, a, b, c, x[5], S12, 0x4787c62a); /* 6 */
FF(c, d, a, b, x[6], S13, 0xa8304613); /* 7 */
FF(b, c, d, a, x[7], S14, 0xfd469501); /* 8 */
FF(a, b, c, d, x[8], S11, 0x698098d8); /* 9 */
FF(d, a, b, c, x[9], S12, 0x8b44f7af); /* 10 */
FF(c, d, a, b, x[10], S13, 0xffff5bb1); /* 11 */
FF(b, c, d, a, x[11], S14, 0x895cd7be); /* 12 */
FF(a, b, c, d, x[12], S11, 0x6b901122); /* 13 */
FF(d, a, b, c, x[13], S12, 0xfd987193); /* 14 */
FF(c, d, a, b, x[14], S13, 0xa679438e); /* 15 */
FF(b, c, d, a, x[15], S14, 0x49b40821); /* 16 */
/* Round 2 */
GG(a, b, c, d, x[1], S21, 0xf61e2562); /* 17 */
GG(d, a, b, c, x[6], S22, 0xc040b340); /* 18 */
GG(c, d, a, b, x[11], S23, 0x265e5a51); /* 19 */
GG(b, c, d, a, x[0], S24, 0xe9b6c7aa); /* 20 */
GG(a, b, c, d, x[5], S21, 0xd62f105d); /* 21 */
GG(d, a, b, c, x[10], S22, 0x2441453); /* 22 */
GG(c, d, a, b, x[15], S23, 0xd8a1e681); /* 23 */
GG(b, c, d, a, x[4], S24, 0xe7d3fbc8); /* 24 */
GG(a, b, c, d, x[9], S21, 0x21e1cde6); /* 25 */
GG(d, a, b, c, x[14], S22, 0xc33707d6); /* 26 */
GG(c, d, a, b, x[3], S23, 0xf4d50d87); /* 27 */
GG(b, c, d, a, x[8], S24, 0x455a14ed); /* 28 */
GG(a, b, c, d, x[13], S21, 0xa9e3e905); /* 29 */
GG(d, a, b, c, x[2], S22, 0xfcefa3f8); /* 30 */
GG(c, d, a, b, x[7], S23, 0x676f02d9); /* 31 */
GG(b, c, d, a, x[12], S24, 0x8d2a4c8a); /* 32 */
/* Round 3 */
HH(a, b, c, d, x[5], S31, 0xfffa3942); /* 33 */
HH(d, a, b, c, x[8], S32, 0x8771f681); /* 34 */
HH(c, d, a, b, x[11], S33, 0x6d9d6122); /* 35 */
HH(b, c, d, a, x[14], S34, 0xfde5380c); /* 36 */
HH(a, b, c, d, x[1], S31, 0xa4beea44); /* 37 */
HH(d, a, b, c, x[4], S32, 0x4bdecfa9); /* 38 */
HH(c, d, a, b, x[7], S33, 0xf6bb4b60); /* 39 */
HH(b, c, d, a, x[10], S34, 0xbebfbc70); /* 40 */
HH(a, b, c, d, x[13], S31, 0x289b7ec6); /* 41 */
HH(d, a, b, c, x[0], S32, 0xeaa127fa); /* 42 */
HH(c, d, a, b, x[3], S33, 0xd4ef3085); /* 43 */
HH(b, c, d, a, x[6], S34, 0x4881d05); /* 44 */
HH(a, b, c, d, x[9], S31, 0xd9d4d039); /* 45 */
HH(d, a, b, c, x[12], S32, 0xe6db99e5); /* 46 */
HH(c, d, a, b, x[15], S33, 0x1fa27cf8); /* 47 */
HH(b, c, d, a, x[2], S34, 0xc4ac5665); /* 48 */
/* Round 4 */
II(a, b, c, d, x[0], S41, 0xf4292244); /* 49 */
II(d, a, b, c, x[7], S42, 0x432aff97); /* 50 */
II(c, d, a, b, x[14], S43, 0xab9423a7); /* 51 */
II(b, c, d, a, x[5], S44, 0xfc93a039); /* 52 */
II(a, b, c, d, x[12], S41, 0x655b59c3); /* 53 */
II(d, a, b, c, x[3], S42, 0x8f0ccc92); /* 54 */
II(c, d, a, b, x[10], S43, 0xffeff47d); /* 55 */
II(b, c, d, a, x[1], S44, 0x85845dd1); /* 56 */
II(a, b, c, d, x[8], S41, 0x6fa87e4f); /* 57 */
II(d, a, b, c, x[15], S42, 0xfe2ce6e0); /* 58 */
II(c, d, a, b, x[6], S43, 0xa3014314); /* 59 */
II(b, c, d, a, x[13], S44, 0x4e0811a1); /* 60 */
II(a, b, c, d, x[4], S41, 0xf7537e82); /* 61 */
II(d, a, b, c, x[11], S42, 0xbd3af235); /* 62 */
II(c, d, a, b, x[2], S43, 0x2ad7d2bb); /* 63 */
II(b, c, d, a, x[9], S44, 0xeb86d391); /* 64 */
state[0] += a;
state[1] += b;
state[2] += c;
state[3] += d;
memset((char *) x, 0, sizeof(x));
}
void MD5_Init(MD5Context * context)
{
context->count[0] = context->count[1] = 0;
context->state[0] = 0x67452301;
context->state[1] = 0xefcdab89;
context->state[2] = 0x98badcfe;
context->state[3] = 0x10325476;
}
void MD5_Update(MD5Context * context,unsigned char * buf, int len)
{
unsigned int i, index, partLen;
index = (unsigned int) ((context->count[0] >> 3) & 0x3F);
if ((context->count[0] += ((unsigned int) len << 3)) <((unsigned int) len << 3))
context->count[1]++;
context->count[1] += ((unsigned int) len >> 29);
partLen = 64 - index;
if (len >= partLen)
{
memcpy((char *) &context->buffer[index], (char *) buf, partLen);
MD5_Transform(context->state, context->buffer);
for (i = partLen; i + 63 < len; i += 64)
MD5_Transform(context->state, &buf[i]);
index = 0;
}
else
{
i = 0;
}
memcpy((char *) &context->buffer[index], (char *) &buf[i],len - i);
}
void MD5_Final(MD5Context * context,unsigned char digest[16])
{
unsigned char bits[8];
unsigned int index, padLen;
MD5_Encode(bits, context->count, 8);
index = (unsigned int) ((context->count[0] >> 3) & 0x3f);
padLen = (index < 56) ? (56 - index) : (120 - index);
MD5_Update(context, PADDING, padLen);
MD5_Update(context, bits, 8);
MD5_Encode(digest, context->state, 16);
memset((char *) context, 0, sizeof(*context));
}
//test
Int main(void)
{
MD5Context context;
u8md5buf[16];
char *str ="a";
int len = strlen(str);
MD5_Init(&context);
MD5_Update(&context,str, len);
MD5_Final(&context, md5buf);
write(STDOUT_FILENO,md5buf, 16);
return 0;
}