[转载]MD5加密算法原理

#include <STRING.H>
#include <STDIO.H>

//! 定义MD5状态数据结构类型
typedef struct{
    unsigned long int    state[4];        // 初始链接变量;保存16字节摘要
    unsigned long int    count[2];        // 明文位数
    unsigned char        PADDING[64];    // 填充位，最大64*8位
    unsigned char        buffer[64];        // 输入缓冲
}MD5_State;

//! MD5转换常量
#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

//! F, G, H and I 基本MD5函数
#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)))

//! 将x循环左移n位
#define ROTATE_LEFT(x, n) (((x) << (n)) | ((x) >> (32-(n))))

//! 4轮运算中FF(第1轮), GG(第2轮), HH(第3轮), and II(第4轮)转换
#define FF(a, b, c, d, x, s, ac) { \
    (a) += F ((b), (c), (d)) + (x) + (unsigned long 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 long 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 long 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 long int)(ac);     (a) = ROTATE_LEFT ((a), (s));     (a) += (b);     }

/******************************************************************************/
//    名称：MD5_memcpy
//    功能：输入输出字节拷贝
//  参数：output:    指向unsigned char类型输出缓冲区
//          input:    指向unsigned char类型输入缓冲区
//          len:        输入数据长度(字节)
//    返回：无

/******************************************************************************/
void MD5_memcpy( unsigned char *output, unsigned char *input, unsigned int len )
{
    unsigned int i;

    for( i = 0; i < len; i++ )
        output[i] = input[i];
}

/******************************************************************************/
//    名称：MD5_memset
//    功能：对MD5运算缓冲区中填充数据
//  参数：output:    指向unsigned char类型缓冲区
//          value:    数据
//          len:        填充大小
//    返回：无

/******************************************************************************/
void MD5_memset( unsigned char *output, int value, unsigned int len )
{
    unsigned int i;

    for( i = 0; i < len; i++ )
        ((char *)output)[i] = (char)value;
}

/******************************************************************************/
//    名称：Encode
//    功能：数据类型轮换(unsigned long char -> unsigned char)
//  参数：output:    指向unsigned char类型输出缓冲区
//          input:    指向unsigned long int类型输入缓冲区
//          len:        输入数据长度(字节)
//    返回：无

/******************************************************************************/
void Encode( unsigned char *output, unsigned long int *input, unsigned 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);
    }
}

/******************************************************************************/
//    名称：Decode
//    功能：数据类型轮换(unsigned char -> unsigned long int)
//  参数：output:    指向unsigned long int类型输出缓冲区
//          input:    指向unsigned char类型输入缓冲区
//          len:        输入数据长度(字节)
//    返回：无

/******************************************************************************/
void Decode( unsigned long int *output, unsigned char *input, unsigned int len )
{
    unsigned int i, j;

    for( i=0, j=0; j<len; i++, j+=4 )
        output[i] = ((unsigned long int)input[j]) | (((unsigned long int)input[j+1]) << 8) |
        (((unsigned long int)input[j+2]) << 16) | (((unsigned long int)input[j+3]) << 24);
}

/******************************************************************************/
//    名称：MD5Init
//    功能：初始链接变量赋值；初始化填充位
//  参数：指向MD5状态数据变量
//    返回：无
//  备注：填充位第1位为1,其余位为0

/******************************************************************************/
void MD5_Init( MD5_State *s )
{
    s->count[0] = s->count[1] = 0;
    //! 初始链接变量
    s->state[0] = 0x67452301;
    s->state[1] = 0xefcdab89;
    s->state[2] = 0x98badcfe;
    s->state[3] = 0x10325476;

    //! 初始填充位(目标形式: 0x80000000......，共计512位)
    MD5_memset( s->PADDING, 0, sizeof(s->PADDING) );
    *(s->PADDING)=0x80;
    //  s->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    };
}

/******************************************************************************/
//    名称：MD5Transform
//    功能：MD5 4轮运算
//  参数：state: 链接变量；block: 子明文分组
//    返回：无
//  备注：4轮共计64步运算

/******************************************************************************/
void MD5_Transform( unsigned long int state[4], unsigned char block[64] )
{
    unsigned long int a = state[0], b = state[1], c = state[2], d = state[3], x[16];

    Decode( x, block, 64 );

    //! 第1轮

    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

    //! 第2轮
    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

    //! 第3轮
    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

    //! 第4轮
    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;

    MD5_memset( (unsigned char*)x, 0, sizeof (x) );
}

/******************************************************************************/
//    名称：MD5_Update
//    功能：明文填充，明文分组，16个子明文分组
//  参数：指向SHA状态变量
//    返回：无

/******************************************************************************/
void MD5_Update( MD5_State *s, unsigned char *input, unsigned int inputLen )
{
    unsigned int i, index, partLen;

    //! 明文填充

    //! 字节数 mod 64
    index = (unsigned int)((s->count[0] >> 3) & 0x3F);

    //! 更新位数
    if((s->count[0] += ((unsigned long int)inputLen << 3))
        < ((unsigned long int)inputLen << 3))
        s->count[1]++;
    s->count[1] += ((unsigned long int)inputLen >> 29);

    partLen = 64 - index;

    //! MD5 4轮运算
    if (inputLen >= partLen)
    {
        MD5_memcpy( (unsigned char*)&s->buffer[index],  (unsigned char*)input, partLen );
        MD5_Transform( s->state, s->buffer );

        for( i = partLen; i + 63 < inputLen; i += 64 )
            MD5_Transform( s->state, &input[i] );

        index = 0;
    }
    else
        i = 0;

    MD5_memcpy ((unsigned char*)&s->buffer[index], (unsigned char*)&input[i], inputLen-i);
}

/******************************************************************************/
//    名称：MD5_Final
//    功能：MD5最后变换
//  参数：strContent:指向文件内容缓冲区; iLength:文件内容长度; output:摘要输出缓冲区
//    返回：无

/******************************************************************************/
void MD5_Final( MD5_State *s, unsigned char digest[16] )
{
    unsigned char bits[8];
    unsigned int index, padLen;

    Encode (bits, s->count, 8);

    //! 长度小于448位(mod 512),对明文进行填充
    index = (unsigned int)((s->count[0] >> 3) & 0x3f);
    padLen = (index < 56) ? (56 - index) : (120 - index);
    MD5_Update( s, s->PADDING, padLen );

    MD5_Update( s, bits, 8);
    Encode( digest, s->state, 16 );

    MD5_memset ((unsigned char*)s, 0, sizeof (*s));
    MD5_Init( s );
}


/******************************************************************************/
//    名称：SHA_digest
//    功能：生成文件摘要
//  参数：strContent:指向文件内容缓冲区; iLength:文件内容长度; output:摘要输出缓冲区
//    返回：无

/******************************************************************************/
void md5_digest( void const *strContent, unsigned int iLength, unsigned char output[16] )
{
    unsigned char *q = (unsigned char*)strContent;
    MD5_State s;

    MD5_Init( &s );
    MD5_Update( &s, q, iLength );
    MD5_Final( &s, output );
}

int main(int argc, char* argv[])
{
    unsigned char output[16] = {0};
    int i = 0;

    md5_digest("Hello World!", strlen("Hello World!"), output);

    for (i = 0; i < 16; i++)
    {
        printf("%02x", output[i]);
    }

    printf("\r\n");
    return 0;
}