MD5源码（C语言描述）

本文介绍MD5源码（C语言描述）。

MD5(Message-Digest Algorithm 5)，即消息摘要算法5，是一种被广泛使用的消息散列算法。散列算法的基础原理是：将数据（如一段文字）经过运算转换为一段固定长度（16/32）的值。主要用于数据防篡改。

1.源码

1)头文件

头文件（MD5.h）主要包括MD5外部函数声明。头文件定义如下。

#ifndef MD5_H
#define MD5_H

#include <stdio.h>
#include <stdint.h>


extern void MD5_String(char *input, uint8_t *result);
extern void MD5_Data(uint8_t *input, uint32_t length, uint8_t *result);
extern void MD5_File(FILE *file, uint8_t *result);


#endif

其中，

a)MD5_String()：用于计算字符串的MD5值。
b)MD5_Data()：用于计算数据的MD5值。
c)MD5_File()：用于计算文件的MD5值。
d)result的结果是1个16字节长度（按16进制表示则为32位长度）的数组。

2)源文件

源文件（MD5. c）主要包括MD5相关外部函数定义。源文件定义如下。

#include "MD5.h"
#include <string.h>
#include <stdlib.h>

/*
 * Constants defined by the MD5 algorithm
 */
#define A   (0x67452301)
#define B   (0xefcdab89)
#define C   (0x98badcfe)
#define D   (0x10325476)

/*
 * Bit-manipulation functions defined by the MD5 algorithm
 */
#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))

typedef struct _MD5_CONTEXT
{
    uint64_t size;        // Size of input in bytes
    uint32_t buffer[4];   // Current accumulation of hash
    uint8_t input[64];    // Input to be used in the next step
    uint8_t digest[16];   // Result of algorithm
}MD5_CONTEXT;

static const uint32_t S[] =
{
    7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22,
    5,  9, 14, 20, 5,  9, 14, 20, 5,  9, 14, 20, 5,  9, 14, 20,
    4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23,
    6, 10, 15, 21, 6, 10, 15, 21, 6, 10, 15, 21, 6, 10, 15, 21
};

static const uint32_t K[] =
{
    0xd76aa478, 0xe8c7b756, 0x242070db, 0xc1bdceee,
    0xf57c0faf, 0x4787c62a, 0xa8304613, 0xfd469501,
    0x698098d8, 0x8b44f7af, 0xffff5bb1, 0x895cd7be,
    0x6b901122, 0xfd987193, 0xa679438e, 0x49b40821,
    0xf61e2562, 0xc040b340, 0x265e5a51, 0xe9b6c7aa,
    0xd62f105d, 0x02441453, 0xd8a1e681, 0xe7d3fbc8,
    0x21e1cde6, 0xc33707d6, 0xf4d50d87, 0x455a14ed,
    0xa9e3e905, 0xfcefa3f8, 0x676f02d9, 0x8d2a4c8a,
    0xfffa3942, 0x8771f681, 0x6d9d6122, 0xfde5380c,
    0xa4beea44, 0x4bdecfa9, 0xf6bb4b60, 0xbebfbc70,
    0x289b7ec6, 0xeaa127fa, 0xd4ef3085, 0x04881d05,
    0xd9d4d039, 0xe6db99e5, 0x1fa27cf8, 0xc4ac5665,
    0xf4292244, 0x432aff97, 0xab9423a7, 0xfc93a039,
    0x655b59c3, 0x8f0ccc92, 0xffeff47d, 0x85845dd1,
    0x6fa87e4f, 0xfe2ce6e0, 0xa3014314, 0x4e0811a1,
    0xf7537e82, 0xbd3af235, 0x2ad7d2bb, 0xeb86d391
};

/*
 * Padding used to make the size (in bits) of the input congruent to 448 mod 512
 */
static const uint8_t PADDING[] =
{
    0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
};

static uint32_t RotateLeft(uint32_t x, uint32_t n);
static void MD5_Init(MD5_CONTEXT *ctx);
static void MD5_Update(MD5_CONTEXT *ctx, uint8_t *input, size_t input_len);
static void MD5_Final(MD5_CONTEXT *ctx);
static void MD5_Step(uint32_t *buffer, uint32_t *input);

/*
 * Rotates a 32-bit word left by n bits
 */
static uint32_t RotateLeft(uint32_t x, uint32_t n)
{
    return (x << n) | (x >> (32 - n));
}

/*
 * Initialize a context
 */
static void MD5_Init(MD5_CONTEXT *ctx)
{
    ctx->size = (uint64_t)0;

    ctx->buffer[0] = (uint32_t)A;
    ctx->buffer[1] = (uint32_t)B;
    ctx->buffer[2] = (uint32_t)C;
    ctx->buffer[3] = (uint32_t)D;
}

/*
 * Add some amount of input to the context
 *
 * If the input fills out a block of 512 bits, apply the algorithm (md5Step)
 * and save the result in the buffer. Also updates the overall size.
 */
static void MD5_Update(MD5_CONTEXT *ctx, uint8_t *input_buffer, size_t input_len)
{
    uint32_t input[16] = {0};
    uint32_t offset = ctx->size % 64;
    ctx->size += (uint64_t)input_len;
    uint32_t i = 0;
    uint32_t j = 0;

    // Copy each byte in input_buffer into the next space in our context input
    for (i = 0; i < input_len; i++)
    {
        ctx->input[offset++] = (uint8_t)(*(input_buffer + i));

        // If we've filled our context input, copy it into our local array input
        // then reset the offset to 0 and fill in a new buffer.
        // Every time we fill out a chunk, we run it through the algorithm
        // to enable some back and forth between cpu and i/o
        if (offset % 64 == 0)
        {
            for (j = 0; j < 16; j++)
            {
                // Convert to little-endian
                // The local variable `input` our 512-bit chunk separated into 32-bit words
                // we can use in calculations
                input[j] = (uint32_t)(ctx->input[(j * 4) + 3]) << 24 |
                           (uint32_t)(ctx->input[(j * 4) + 2]) << 16 |
                           (uint32_t)(ctx->input[(j * 4) + 1]) <<  8 |
                           (uint32_t)(ctx->input[(j * 4)]);
            }
            MD5_Step(ctx->buffer, input);
            offset = 0;
        }
    }
}

/*
 * Pad the current input to get to 448 bytes, append the size in bits to the very end,
 * and save the result of the final iteration into digest.
 */
static void MD5_Final(MD5_CONTEXT *ctx)
{
    uint32_t input[16] = {0};
    uint32_t offset = ctx->size % 64;
    uint32_t padding_length = (offset < 56) ? (56 - offset) : ((56 + 64) - offset);
    uint32_t i = 0;
    uint32_t j = 0;

    // Fill in the padding and undo the changes to size that resulted from the update
    MD5_Update(ctx, PADDING, padding_length);
    ctx->size -= (uint64_t)padding_length;

    // Do a final update (internal to this function)
    // Last two 32-bit words are the two halves of the size (converted from bytes to bits)
    for (j = 0; j < 14; j++)
    {
        input[j] = (uint32_t)(ctx->input[(j * 4) + 3]) << 24 |
                   (uint32_t)(ctx->input[(j * 4) + 2]) << 16 |
                   (uint32_t)(ctx->input[(j * 4) + 1]) <<  8 |
                   (uint32_t)(ctx->input[(j * 4)]);
    }
    input[14] = (uint32_t)(ctx->size * 8);
    input[15] = (uint32_t)((ctx->size * 8) >> 32);

    MD5_Step(ctx->buffer, input);

    // Move the result into digest (convert from little-endian)
    for (i = 0; i < 4; i++)
    {
        ctx->digest[(i * 4) + 0] = (uint8_t)((ctx->buffer[i] & 0x000000FF));
        ctx->digest[(i * 4) + 1] = (uint8_t)((ctx->buffer[i] & 0x0000FF00) >>  8);
        ctx->digest[(i * 4) + 2] = (uint8_t)((ctx->buffer[i] & 0x00FF0000) >> 16);
        ctx->digest[(i * 4) + 3] = (uint8_t)((ctx->buffer[i] & 0xFF000000) >> 24);
    }
}

/*
 * Step on 512 bits of input with the main MD5 algorithm.
 */
static void MD5_Step(uint32_t *buffer, uint32_t *input)
{
    uint32_t AA = buffer[0];
    uint32_t BB = buffer[1];
    uint32_t CC = buffer[2];
    uint32_t DD = buffer[3];

    uint32_t E = 0;
    uint32_t temp = 0;

    uint32_t i = 0;
    uint32_t j = 0;

    for(i = 0; i < 64; i++)
    {
        switch (i / 16)
        {
            case (0):
            {
                E = F(BB, CC, DD);
                j = i;
                break;
            }
            case (1):
            {
                E = G(BB, CC, DD);
                j = ((i * 5) + 1) % 16;
                break;
            }
            case (2):
            {
                E = H(BB, CC, DD);
                j = ((i * 3) + 5) % 16;
                break;
            }
            default:
            {
                E = I(BB, CC, DD);
                j = (i * 7) % 16;
                break;
            }
        }

        temp = DD;
        DD = CC;
        CC = BB;
        BB = BB + RotateLeft(AA + E + K[i] + input[j], S[i]);
        AA = temp;
    }

    buffer[0] += AA;
    buffer[1] += BB;
    buffer[2] += CC;
    buffer[3] += DD;
}

/*
 * Functions that run the algorithm on the provided input and put the digest into result.
 * result should be able to store 16 bytes.
 */
void MD5_String(char *input, uint8_t *result)
{
    MD5_CONTEXT ctx;

    if ((input == NULL) || (result == NULL))
    {
        return ;
    }

    MD5_Init(&ctx);
    MD5_Update(&ctx, (uint8_t *)input, strlen(input));
    MD5_Final(&ctx);

    memcpy(result, ctx.digest, 16);
}

void MD5_Data(uint8_t *input, uint32_t length, uint8_t *result)
{
    MD5_CONTEXT ctx;

    if ((input == NULL) || (result == NULL) || (length == 0))
    {
        return ;
    }

    MD5_Init(&ctx);
    MD5_Update(&ctx, (uint8_t *)input, length);
    MD5_Final(&ctx);

    memcpy(result, ctx.digest, 16);
}

void MD5_File(FILE *file, uint8_t *result)
{
    char *input_buffer = NULL;
    size_t input_size = 0;
    MD5_CONTEXT ctx;

    if ((file == NULL) || (result == NULL))
    {
        return ;
    }

    input_buffer = malloc(1024);

    MD5_Init(&ctx);

    while ((input_size = fread(input_buffer, 1, 1024, file)) > 0)
    {
        MD5_Update(&ctx, (uint8_t *)input_buffer, input_size);
    }

    MD5_Final(&ctx);

    free(input_buffer);

    memcpy(result, ctx.digest, 16);
}

2.测试

这里以计算字符串为例。

#include <stdio.h>
#include "MD5.h"


int main()
{
    uint8_t md5[16] = {0};
    uint32_t i = 0;

    MD5_String("Hello,World", md5);

    for (i = 0; i < 16; i++)
    {
        printf("%x", md5[i]);
    }

    printf("\r\n");

    return 0;
}

计算结果如下：