What libraries are needed to link OpenSSL?

Question

C++ / C#

When compiled without specifying either, it produces the following:

C:\Users\admin\AppData\Local\Temp\ccWyoIvB.o:a.c:(.text+0x1d): undefined reference to `ERR_print_errors_fp'
C:\Users\admin\AppData\Local\Temp\ccWyoIvB.o:a.c:(.text+0x34): undefined reference to `SSL_load_error_strings'
C:\Users\admin\AppData\Local\Temp\ccWyoIvB.o:a.c:(.text+0x39): undefined reference to `SSL_library_init'
C:\Users\admin\AppData\Local\Temp\ccWyoIvB.o:a.c:(.text+0x4d): undefined reference to `SSL_CTX_free'
C:\Users\admin\AppData\Local\Temp\ccWyoIvB.o:a.c:(.text+0x58): undefined reference to `BIO_free_all'
C:\Users\admin\AppData\Local\Temp\ccWyoIvB.o:a.c:(.text+0x69): undefined reference to `TLSv1_2_client_method'
C:\Users\admin\AppData\Local\Temp\ccWyoIvB.o:a.c:(.text+0x89): undefined reference to `SSL_CTX_new'
C:\Users\admin\AppData\Local\Temp\ccWyoIvB.o:a.c:(.text+0xa9): undefined reference to `BIO_new_ssl_connect'
C:\Users\admin\AppData\Local\Temp\ccWyoIvB.o:a.c:(.text+0x112): undefined reference to `BIO_ctrl'
C:\Users\admin\AppData\Local\Temp\ccWyoIvB.o:a.c:(.text+0x138): undefined reference to `SSL_ctrl'
C:\Users\admin\AppData\Local\Temp\ccWyoIvB.o:a.c:(.text+0x15d): undefined reference to `BIO_ctrl'
C:\Users\admin\AppData\Local\Temp\ccWyoIvB.o:a.c:(.text+0x180): undefined reference to `BIO_ctrl'
C:\Users\admin\AppData\Local\Temp\ccWyoIvB.o:a.c:(.text+0x1bd): undefined reference to `SSL_CTX_load_verify_locations'
C:\Users\admin\AppData\Local\Temp\ccWyoIvB.o:a.c:(.text+0x1db): undefined reference to `SSL_get_verify_result'
C:\Users\admin\AppData\Local\Temp\ccWyoIvB.o:a.c:(.text+0x235): undefined reference to `BIO_puts'
C:\Users\admin\AppData\Local\Temp\ccWyoIvB.o:a.c:(.text+0x270): undefined reference to `BIO_read'
collect2.exe: error: ld returned 1 exit status

When adding -lssl:

C:\Users\admin\AppData\Local\Temp\cc2363zP.o:a.c:(.text+0x1d): undefined reference to `ERR_print_errors_fp'
C:\Users\admin\AppData\Local\Temp\cc2363zP.o:a.c:(.text+0x34): undefined reference to `SSL_load_error_strings'
C:\Users\admin\AppData\Local\Temp\cc2363zP.o:a.c:(.text+0x39): undefined reference to `SSL_library_init'
C:\Users\admin\AppData\Local\Temp\cc2363zP.o:a.c:(.text+0x58): undefined reference to `BIO_free_all'
C:\Users\admin\AppData\Local\Temp\cc2363zP.o:a.c:(.text+0x69): undefined reference to `TLSv1_2_client_method'
C:\Users\admin\AppData\Local\Temp\cc2363zP.o:a.c:(.text+0x112): undefined reference to `BIO_ctrl'
C:\Users\admin\AppData\Local\Temp\cc2363zP.o:a.c:(.text+0x15d): undefined reference to `BIO_ctrl'
C:\Users\admin\AppData\Local\Temp\cc2363zP.o:a.c:(.text+0x180): undefined reference to `BIO_ctrl'
C:\Users\admin\AppData\Local\Temp\cc2363zP.o:a.c:(.text+0x235): undefined reference to `BIO_puts'
C:\Users\admin\AppData\Local\Temp\cc2363zP.o:a.c:(.text+0x270): undefined reference to `BIO_read'
collect2.exe: error: ld returned 1 exit status

When adding -lcrypto and -lssl:

C:\Users\admin\AppData\Local\Temp\ccSOQAah.o:a.c:(.text+0x34): undefined reference to `SSL_load_error_strings'
C:\Users\admin\AppData\Local\Temp\ccSOQAah.o:a.c:(.text+0x39): undefined reference to `SSL_library_init'
C:\Users\admin\AppData\Local\Temp\ccSOQAah.o:a.c:(.text+0x69): undefined reference to `TLSv1_2_client_method'
collect2.exe: error: ld returned 1 exit status

Compiler: MinGw
When I tried using cmake, it was exactly the same.
What libraries need to be specified for linking to occur?
The code:
gcc a.c -lssl -lcrypto

#include <stdio.h>
#include <stdlib.h>
#include <openssl/bio.h>
#include <openssl/err.h>
#include <openssl/ssl.h>

#define BuffSize 1024

void report_and_exit(const char* msg) {
  perror(msg);
  ERR_print_errors_fp(stderr);
  exit(-1);
}

void init_ssl() {
  SSL_load_error_strings();
  SSL_library_init();
}

void cleanup(SSL_CTX* ctx, BIO* bio) {
  SSL_CTX_free(ctx);
  BIO_free_all(bio);
}

void secure_connect(const char* hostname) {
  char name[BuffSize];
  char request[BuffSize];
  char response[BuffSize];

  const SSL_METHOD* method = TLSv1_2_client_method();
  if (NULL == method) report_and_exit("TLSv1_2_client_method...");

  SSL_CTX* ctx = SSL_CTX_new(method);
  if (NULL == ctx) report_and_exit("SSL_CTX_new...");

  BIO* bio = BIO_new_ssl_connect(ctx);
  if (NULL == bio) report_and_exit("BIO_new_ssl_connect...");

  SSL* ssl = NULL;

  sprintf(name, "%s:%s", hostname, "https");
  BIO_get_ssl(bio, &ssl);
  SSL_set_mode(ssl, SSL_MODE_AUTO_RETRY);
  BIO_set_conn_hostname(bio, name);

  if (BIO_do_connect(bio) <= 0) {
    cleanup(ctx, bio);
    report_and_exit("BIO_do_connect...");
  }

  if (!SSL_CTX_load_verify_locations(ctx,
                                      "/etc/ssl/certs/ca-certificates.crt",
                                      "/etc/ssl/certs/"))
    report_and_exit("SSL_CTX_load_verify_locations...");

  long verify_flag = SSL_get_verify_result(ssl);
  if (verify_flag != X509_V_OK)
    fprintf(stderr,
            "##### Certificate verification error (%i) but continuing...\n",
            (int) verify_flag);

  sprintf(request,
          "GET / HTTP/1.1\x0D\x0AHost: %s\x0D\x0A\x43onnection: Close\x0D\x0A\x0D\x0A",
          hostname);
  BIO_puts(bio, request);

  while (1) {
    memset(response, '\0', sizeof(response));
    int n = BIO_read(bio, response, BuffSize);
    if (n <= 0) break;
  puts(response);
  }

  cleanup(ctx, bio);
}

int main() {
  init_ssl();

  const char* hostname = "www.google.com:443";
  fprintf(stderr, "Trying an HTTPS connection to %s...\n", hostname);
  secure_connect(hostname);

return 0;
}

Answer 1

The only thing he did.
sudo apt-get install libssl-dev