以SHA-1为例的HASH算法代码实现

以下是以SHA-1为例的HASH算法代码实现（使用C语言）：

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

#define BLOCK_SIZE 64

uint32_t h0, h1, h2, h3, h4;

uint32_t k[] = {
    0x5a827999, 0x6ed9eba1, 0x8f1bbcdc, 0xca62c1d6
};

void sha1_transform(uint8_t *message, uint32_t length) {
    uint32_t w[80];
    uint32_t a, b, c, d, e, f, k, temp;
    uint32_t i, j;
    
    for (i = 0; i < length / BLOCK_SIZE; i++) {
        memcpy(w, &message[i * BLOCK_SIZE], BLOCK_SIZE);
        
        for (j = 16; j < 80; j++) {
            w[j] = w[j - 3] ^ w[j - 8] ^ w[j - 14] ^ w[j - 16];
            w[j] = (w[j] << 1) | (w[j] >> 31);
        }
        
        a = h0;
        b = h1;
        c = h2;
        d = h3;
        e = h4;
        
        for (j = 0; j < 80; j++) {
            if (j < 20) {
                f = (b & c) | ((~b) & d);
                k = 0x5a827999;
            } else if (j < 40) {
                f = b ^ c ^ d;
                k = 0x6ed9eba1;
            } else if (j < 60) {
                f = (b & c) | (b & d) | (c & d);
                k = 0x8f1bbcdc;
            } else {
                f = b ^ c ^ d;
                k = 0xca62c1d6;
            }
            
            temp = (a << 5) | (a >> 27);
            temp += f + e + k + w[j];
            e = d;
            d = c;
            c = (b << 30) | (b >> 2);
            b = a;
            a = temp;
        }
        
        h0 += a;
        h1 += b;
        h2 += c;
        h3 += d;
        h4 += e;
    }
}

void sha1_hash(uint8_t *message, uint32_t length, uint8_t *digest) {
    uint32_t i;
    uint8_t *padded_message;
    uint32_t padded_length;
    
    h0 = 0x67452301;
    h1 = 0xefcdab89;
    h2 = 0x98badcfe;
    h3 = 0x10325476;
    h4 = 0xc3d2e1f0;
    
    padded_length = length;
    while ((padded_length + 1 + 8) % BLOCK_SIZE != 0) {
        padded_length++;
    }
    
    padded_message = (uint8_t *) malloc(padded_length + 1 + 8);
    memcpy(padded_message, message, length);
    padded_message[length] = 0x80;
    memset(&padded_message[length + 1], 0, padded_length - length);
    padded_length += 1 + 8;
    
    *((uint64_t *) &padded_message[padded_length - 8]) = length * 8;
    
    sha1_transform(padded_message, padded_length);
    
    free(padded_message);
    
    for (i = 0; i < 4; i++) {
        digest[i] = (h0 >> (24 - i * 8)) & 0xff;
        digest[i + 4] = (h1 >> (24 - i * 8)) & 0xff;
        digest[i + 8] = (h2 >> (24 - i * 8)) & 0xff;
        digest[i + 12] = (h3 >> (24 - i * 8)) & 0xff;
        digest[i + 16] = (h4 >> (24 - i * 8)) & 0xff;
    }
}

int main() {
    uint8_t message[] = "Hello, world!";
    uint8_t digest[20];
    uint32_t i;
    
    sha1_hash(message, strlen(message), digest);
    
    printf("SHA-1 digest:\n");
    for (i = 0; i < 20; i++) {
        printf("%02x", digest[i]);
    }
    printf("\n");
    
    return 0;
}

在程序中，我们定义了五个32位的变量h0、h1、h2、h3、h4，作为SHA-1算法的初始哈希值。在SHA-1算法中，每个消息块64个字节，我们定义BLOCK_SIZE宏来表示这个值。SHA-1算法中用到的常量k也定义在程序中。函数sha1_transform实现了SHA-1中的一次消息块变换，函数sha1_hash实现了SHA-1的哈希函数。在main函数中，我们测试了SHA-1算法的实现。