MD5 C源码的工作原理是什么？

MD5（Message Digest Algorithm 5）是一种广泛使用的加密散列函数，用于生成数据的128位（16字节）哈希值。它最初由Ronald Rivest在1992年设计，并被广泛用于确保数据完整性和验证数据一致性。，，以下是一个简单的C语言实现的MD5算法示例：，，“`c，#include，#include，#include，#include，，// MD5 context.，typedef struct {， uint32_t state[4]; // state (ABCD)， uint32_t count[2]; // number of bits, modulo 2^64 (lsb first)， unsigned char buffer[64]; // input buffer，} MD5_CTX;，，void MD5Init(MD5_CTX* context);，void MD5Update(MD5_CTX* context, unsigned char* input, unsigned int length);，void MD5Final(unsigned char[16], MD5_CTX* context);，void Transform(uint32_t block[4], uint32_t const in[16]);，，unsigned char* MD5(const unsigned char* d, size_t n, unsigned char* md);，，// The main function to test the MD5 implementation.，int main() {， unsigned char digest[16];， const char* string = “hello world”;， MD5((unsigned char*)string, strlen(string), digest);， char mdString[33];， for (int i = 0; i< 16; i++)， sprintf(mdString + i * 2, "%02x", (unsigned int)digest[i]);， printf("MD5 digest: %s，", mdString);， return 0;，}，，// Function to copy a byte array into a hexadecimal string.，void binToHexStr(unsigned char* src, char* dst, int len) {， char* dp = dst;， while (len) {， sprintf(dp, "%02x", *src++);， dp += 2;， }， *dp = '';，}，，unsigned char* MD5(const unsigned char* d, size_t n, unsigned char* md) {， MD5_CTX c;， MD5Init(&c);， MD5Update(&c, d, n);， MD5Final(md, &c);， return md;，}，，void MD5Init(MD5_CTX* context) {， context>count[0] = context>count[1] = 0;， // Load magic initialization constants.， 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 length) {， size_t index = context>count[0] >> 3 & 0x3f; // Index into the buffer.， if (index + length >= 64) {， memcpy(context>buffer + index, input, 64 index);， Transform(context>state, context>buffer);， input += 64 index;， length = 64 index;， index = 0;， }， while (length >= 64) {， Transform(context>state, input);， input += 64;， length = 64;， }， memcpy(context>buffer + index, input, length);， context>count[0] += (lengthcount[1] += (length >> 29);，}，，void MD5Final(unsigned char[16], MD5_CTX* context) {， unsigned char pad[64];， size_t index = context>count[0] >> 3 & 0x3f; // Index into the buffer.， unsigned int padLen = (index< 56) ? (56 index) : (120 index);， pad[0] = 0x80; // Padding value.， memset(pad + 1, 0, padLen 1); // Padding bytes.， MD5Update(context, pad, padLen);， // Store state in array.， unsigned char* state = (unsigned char*)context>state;， // Littleendian convention is used here.， unsigned char digest[16];， memcpy(digest, state, 16);， memset(state, 0, 64); // Clear the state.， // Save the final count.， context>count[0] = ~context>count[0];， context>count[1] = ~context>count[1];， MD5Update(context, (unsigned char*)context>count, 8);， // Save the final state.， memcpy(digest + 16, state, 16);， // Encode the result as a string of hex digits.， binToHexStr(digest, (char*)digest, 32);，}，，void Transform(uint32_t block[4], uint32_t const in[16]) {， uint32_t a = block[0], b = block[1], c = block[2], d = block[3], x[16];， uint32_t temp;， memcpy(x, in, 64);， // Round 1， temp = (b & c) | (~b & d);， a += temp + x[ 0];， temp = (d & a) | (~d & c);， a += temp + x[ 4];， temp = b ^ c ^ d;， a += temp + x[ 8];， temp = c ^ d ^ a;， a += temp + x[12];， temp = (a & b) | (a & c) | (b & c);， a += temp + x[ 1];， temp = (a & d) | (b & d) | (c & d);， a += temp + x[ 5];， temp = a ^ b ^ c ^ d;， a += temp + x[ 9];， temp = (a & b) | (a & c) | (b & c);， a += temp + x[2];， temp = (a & d) | (b & d) | (c & d);， a += temp + x[ 6];， temp = a ^ b ^ c ^ d;， a += temp + x[10];， temp = (a & b) | (a & c) | (b & c);， a += temp + x[ 3];， temp = (a & d) | (b & d) | (c & d);， a += temp + x[ 7];， temp = a ^ b ^ c ^ d;， a += temp + x[11];， temp = (a & b) | (a & c) | (b & c);， a += temp + x[ 4];， temp = (a & d) | (b & d) | (c & d);， a += temp + x[12];， temp = a ^ b ^ c ^ d;， a += temp + x[13];， temp = (a & b) | (a & c) | (b & c);， a += temp + x[ 5];， temp = (a & d) | (b & d) | (c & d);， a += temp + x[14];， temp = a ^ b ^ c ^ d;， a += temp + x[ 8];， temp = (a & b) | (a & c) | (b & c);， a += temp + x[ 6];， temp = (a & d) | (b & d) | (c & d);， a += temp + x[15];， temp = a ^ b ^ c ^ d;， a += temp + x[ 9];， temp = (a & b) | (a & c) | (b & d);， a += temp + x[10];， temp = (a & c) | (a & d) | (a & b);， a += temp + x[14];， temp = (a & d) | (a & b) | (a & c);， a += temp + x[13];， temp = (a & b) | (a & c) | (a & d);， a += temp + x[12];， temp = (a & c) | (a & d) | (a & b);， a += temp + x[11];， temp = (a & d) | (a & b) | (a & c);， a += temp + x[15];， temp = (a & b) | (a & c) | (a & d);， a += temp + x[ 8];， temp = (a & c) | (a & d) | (a & b);， a += temp + x[ 7];， temp = (a & d) | (a & b) | (a & c);， a += temp + x[ 6];， temp = (a & b) | (a & c) | (a & d);， a += temp + x[ 5];， temp = (a & c) | (a & d) | (a & b);， a += temp + x[4];， temp = (a & d) | (a & b) | (a & c);， a += temp + x[3];， temp = (a & b) | (a & c) | (a & d);， a += temp + x[2];， temp = (a & c) | (a & d) | (a & b);， a += temp + x[1];， block[0] += a;， block[1] += b;， block[2] += c;， block[3] += d;，}，，

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
// 左移操作宏定义
#define LEFTROTATE(x, c) (((x) << (c)) | ((x) >> (32  (c))))
// MD5算法中的四个非线性函数
#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)))
// MD5算法的主循环
void md5_main_loop(uint32_t state[4], uint32_t count[2], uint8_t buffer[64]) {
    uint32_t a, b, c, d, f, g, temp;
    uint32_t *x = (uint32_t *)buffer;
    a = state[0];
    b = state[1];
    c = state[2];
    d = state[3];
    for (int i = 0; i < 64; i++) {
        if (i < 16) {
            f = F(b, c, d);
            g = i;
        } else if (i < 32) {
            f = G(b, c, d);
            g = (5 * i + 1) % 16;
        } else if (i < 48) {
            f = H(b, c, d);
            g = (3 * i + 5) % 16;
        } else {
            f = I(b, c, d);
            g = (7 * i) % 16;
        }
        temp = d;
        d = c;
        c = b;
        b = b + LEFTROTATE((a + f + k[i] + x[g]), r[i]);
        a = temp;
    }
    state[0] += a;
    state[1] += b;
    state[2] += c;
    state[3] += d;
}
// MD5算法初始化
void md5_init(uint32_t state[4], uint32_t count[2]) {
    state[0] = 0x67452301;
    state[1] = 0xefcdab89;
    state[2] = 0x98badcfe;
    state[3] = 0x10325476;
    count[0] = count[1] = 0;
}
// MD5算法处理数据块
void md5_process_block(uint32_t state[4], uint32_t count[2], uint8_t data[64]) {
    uint32_t n = (count[0] >> 3) & 0x3F;
    uint8_t *p = data + n * 4;
    uint32_t i;
    for (i = 0; i < 16; i++, p += 4) {
        state[i] = (uint32_t)(p[0]) | ((uint32_t)(p[1]) << 8) | ((uint32_t)(p[2]) << 16) | ((uint32_t)(p[3]) << 24);
    }
    md5_main_loop(state, count, data);
}
// MD5算法更新状态和计数器
void md5_update(uint32_t state[4], uint32_t count[2], uint8_t data[], uint32_t len) {
    uint32_t i, index, partlen;
    index = (count[0] >> 3) & 0x3F;
    count[0] += len << 3;
    if (count[0] < (len << 3)) {
        count[1]++;
    }
    count[1] += len >> 29;
    partlen = 64  index;
    if (len >= partlen) {
        memcpy(&data[index], data, partlen);
        md5_process_block(state, count, data);
        for (i = partlen; i + 63 < len; i += 64) {
            md5_process_block(state, count, data + i);
        }
        index = 0;
    } else {
        i = 0;
    }
    memcpy(&data[index], data + i, len  i);
}
// MD5算法结束处理，输出结果
void md5_finish(uint32_t state[4], uint8_t digest[16]) {
    uint32_t i;
    uint8_t *p = (uint8_t *)digest;
    for (i = 0; i < 4; i++) {
        p[i] = (uint8_t)(state[i] & 0xff);
        p[i + 4] = (uint8_t)((state[i] >> 8) & 0xff);
        p[i + 8] = (uint8_t)((state[i] >> 16) & 0xff);
        p[i + 12] = (uint8_t)((state[i] >> 24) & 0xff);
    }
}
// MD5算法主函数
void md5(uint8_t data[], uint32_t len, uint8_t digest[16]) {
    uint32_t state[4], count[2];
    md5_init(state, count);
    md5_update(state, count, data, len);
    md5_finish(state, digest);
}