? 大家都知道，MD5是一種摘要運算算法，關于更多的摘要算法，可以參考我之前的一篇文章：摘要算法匯總

今天要給大家帶來的是MD5摘要運算的源碼實現，廢話不多說，直接上源碼：

先看頭文件，什么了一些結構體定義和操作宏定義，以及導出的3個API接口：

#ifndef __MD5_H__
#define __MD5_H__

#ifdef __cplusplus
extern "C" {
#endif /* __cplusplus */

#include 

typedef struct _md5_ctx_t {
    uint32_t                count[2];
    uint32_t                state[4];
    uint8_t                 buffer[64];
} md5_ctx_t;

#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 MD5_DIGEST_LEN      16

#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; \
}

extern void crypto_md5_init(md5_ctx_t *ctx);
extern void crypto_md5_update(md5_ctx_t *ctx, uint8_t *in, uint32_t in_len);
extern void crypto_md5_final(md5_ctx_t *ctx, uint8_t digest[MD5_DIGEST_LEN]);

#ifdef __cplusplus
}
#endif /* __cplusplus */

#endif /*__MD5_H__*/

接下來，上實現源碼：

#include 
#include 

#include "md5.h"

static const 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 crypto_md5_init(md5_ctx_t *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;
}

static void crypto_md5_decode(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;
    }
}

static void crypto_md5_transform(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];

    crypto_md5_decode(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;
}

void crypto_md5_update(md5_ctx_t *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);
        crypto_md5_transform(context->state, context->buffer);

        for (i = partlen; i+64 <= inputlen; i+=64) {
            crypto_md5_transform(context->state, &input[i]);
        }
        index = 0;
    } else {
        i = 0;
    }
    memcpy(&context->buffer[index], &input[i], inputlen-i);
}

static void crypto_md5_encode(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 crypto_md5_final(md5_ctx_t *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);
    crypto_md5_encode(bits, context->count, 8);
    crypto_md5_update(context, (unsigned char *)PADDING, padlen);
    crypto_md5_update(context, bits, 8);
    crypto_md5_encode(digest, context->state, 16);
}

我們先寫一段測試代碼測試一下看看：

#include 
#include 

#include "md5.h"

int main(int argc, const char *argv[])
{
	const char *data = "C1D0F8FB4958670DBA40AB1F3752EF0D";
	uint8_t digest_calc[MD5_DIGEST_LEN];
	uint8_t digest_exp[MD5_DIGEST_LEN] = "\x4C\x61\x8F\xD1\x4C\x14\x88\x1E\xFB\x13\x35\x2E\x40\x04\x73\xB1";
	md5_ctx_t ctx;
	const char *p_calc = data;
	uint8_t data_bytes[128];
	uint16_t len_bytes;
	char data_str[128];

	if (argc > 1) {
		p_calc = argv[1];
	}

	crypto_md5_init(&ctx);
	crypto_md5_update(&ctx, (uint8_t *)p_calc, strlen(p_calc));
	crypto_md5_final(&ctx, digest_calc);

	if (!memcmp(digest_calc, digest_exp, sizeof(digest_calc))) {
		printf("MD5 digest test OK\n");
	} else {
		//log_hexdump("digest_calc", digest_calc, sizeof(digest_calc));
		//log_hexdump("digest_exp", digest_exp, sizeof(digest_exp));
		printf("MD5 digest test FAIL\n");
	}

	return 0;
}

這個測試案例，是計算一段字符串："C1D0F8FB4958670DBA40AB1F3752EF0D"的MD5摘要，然后期往的MD5摘要是下面的32字節數據：

"\x4C\x61\x8F\xD1\x4C\x14\x88\x1E\xFB\x13\x35\x2E\x40\x04\x73\xB1"

通過取得計算的結果與期望值進行比對，進而得出運算結果正確與否。

通過運行測試程序，可以發現，運算結果正常。

也可以跟一些算法小工具的結果做下對比，發現，結果也是沒有問題的。

以上就是本次對MD5源碼的測試，本案例的所有源代碼，均可以在我的github上面找到，對你有幫助的話，請幫忙點個star呦，先謝謝了。

更多參考鏈接
[1] 【安全算法的github倉庫】
[2] 【安全算法之概述】一文帶你簡要了解常見常用的安全算法