hmacsha256 with openssl

hmacsha256.c

#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <openssl/ssl.h>
#include <openssl/err.h>
#include <openssl/hmac.h>


#include <stdlib.h>

// gcc hmacsha256.c -lcrypto -lssl -o h

unsigned char* hmac_sha256(const char *key, int keylen, unsigned char *data, int datalen, unsigned char *result, unsigned int *resultlen) {
    return HMAC(EVP_sha256(), key, keylen, (unsigned char*)data, datalen, result, resultlen);
}


int main(int argc, char **argv)
{
 
    char key[] = "mysecretkey";
    char data[] = "This is the message to be authenticated";

    unsigned char result[EVP_MAX_MD_SIZE];
    unsigned int resultlen;

    hmac_sha256(key, strlen(key), data, strlen(data), result, &resultlen);

    printf("HMAC-SHA256: ");
    for (int i = 0; i < resultlen; i++) {
        printf("%02x", result[i]);
    }
    printf("\n");

}