#include <stdio.h>

#include <string.h>

#include <openssl/hmac.h>

int main() {

// The secret key for hashing

const char key[] = "012345678";

// The data that we're going to hash

char data[] = "hello world";

// Be careful of the length of string with the choosen hash engine. SHA1 needed 20 characters.

// Change the length accordingly with your choosen hash engine.

unsigned char* result;

unsigned int len = 20;

result = (unsigned char*)malloc(sizeof(char) * len);

HMAC_CTX ctx;

HMAC_CTX_init(&ctx);

// Using sha1 hash engine here.

// You may use other hash engines. e.g EVP_md5(), EVP_sha224, EVP_sha512, etc

HMAC_Init_ex(&ctx, key, strlen(key), EVP_sha1(), NULL);

HMAC_Update(&ctx, (unsigned char*)&data, strlen(data));

HMAC_Final(&ctx, result, &len);

HMAC_CTX_cleanup(&ctx);

printf("HMAC digest: ");

for (int i = 0; i != len; i++)

printf("%02x", (unsigned int)result[i]);

printf("\n");

free(result);

return 0;

}