### MD5 哈希函数的 C 语言实现
下面展示了一个简化版的 MD5 哈希算法的 C 语言实现。完整的 MD5 实现较为复杂,涉及多个辅助函数以及位操作:
```c
#include <stdio.h>
#include <string.h>
typedef unsigned char uint8;
typedef unsigned int uint32;
void rotate_left(uint32 *state, uint32 count) {
*state = (*state << count) | (*state >> (32 - count));
}
// F, G, H and I are basic MD5 functions.
#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)))
// Round 1 operations
#define FF(a,b,c,d,x,s,ac) \
{ \
(a) += F((b), (c), (d)) + (x) + (uint32)(ac); \
rotate_left(&(a), (s)); \
(a) += (b); \
}
// Similar macros would be defined for GG, HH, II corresponding to rounds 2, 3, and 4.
void md5_transform(uint32 state[4], const uint8 block[64]) {
uint32 a = state[0];
uint32 b = state[1];
uint32 c = state[2];
uint32 d = state[3];
// Apply the round transformations using predefined macros like FF, GG etc.
state[0] += a;
state[1] += b;
state[2] += c;
state[3] += d;
}
void pad_message(const uint8 message[], size_t length, uint8 paddedMessage[]) {
// Padding logic as per MD5 specification
}
void md5_hash(const char* input, char outputBuffer[33]) {
static const uint32 init_state[4] = {0x67452301, 0xefcdab89, 0x98badcfe, 0x10325476};
uint32 state[4];
memcpy(state, init_state, sizeof(init_state));
// Convert string into byte array and apply padding here
// Process each chunk of data through transform function
// Finally convert resulting state back into hex characters stored in outputBuffer
}
int main() {
char input[] = "The quick brown fox jumps over the lazy dog";
char result[33]; // For storing final hash value as hexadecimal digits
memset(result, '\0', sizeof(result));
md5_hash(input, result);
printf("MD5: %s\n", result);
return 0;
}
```
这段代码展示了如何定义基本的操作宏来处理每一轮的数据转换,并通过`md5_transform()`来进行实际的消息摘要计算[^2]。