#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <linux/if_alg.h>
#include <errno.h>

int main(void)
{
  int opfd;
  int tfmfd;
  struct sockaddr_alg sa = {
    .salg_family = AF_ALG,
    .salg_type = "hash",
    .salg_name = "md5"
  };
  char buf[20];
  int i;

  tfmfd = socket(AF_ALG, SOCK_SEQPACKET, 0);

  bind(tfmfd, (struct sockaddr *)&sa, sizeof(sa));

  opfd = accept(tfmfd, NULL, 0);

  write(opfd, "abc", 3);
  if (read(opfd, buf, 16) == -1) {
    printf("ERROR: %d\n", errno);
    exit(-1);
  }

  for (i = 0; i < 16; i++) {
    printf("%02x", (unsigned char)buf[i]);
  }
  printf("\n");

  close(opfd);
  close(tfmfd);

  return 0;
}