#include <openssl/evp.h>

int main(void)
{
  const char *const name = "MD5";
  const unsigned char key[] = "\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b";
  const int key_len = 16;
  const unsigned char data[] = "Hi There";
  const int data_len = 8;
  
  EVP_MD_CTX *ctx;
  EVP_PKEY *pkey;
  unsigned char buf[EVP_MAX_MD_SIZE];
  size_t buf_len;
  int ret;
  size_t i, n;

  ctx = EVP_MD_CTX_new();
  if (ctx == NULL) abort();

  pkey = EVP_PKEY_new_mac_key(EVP_PKEY_HMAC, NULL, key, key_len);
  if (pkey == NULL) abort();
  ret = EVP_DigestSignInit(ctx, NULL, EVP_get_digestbyname(name), NULL, pkey);
  if (ret != 1) abort();
  EVP_PKEY_free(pkey);

  ret = EVP_DigestSignUpdate(ctx, data, data_len);
  if (ret != 1) abort();
 
  for (n = 0; n < 2; n += 1) {
    ret = EVP_DigestSignFinal(ctx, buf, &buf_len);
    if (ret != 1) abort();

    printf("0x");
    for (i = 0; i < buf_len; i += 1)
      printf("%02x", buf[i]);
    printf("\n");
  }

  return 0;
}