OpenSSL is a widely used open source library that provides SSL and TLS services to applications. We use it in this chapter for secure connections required by HTTPS.
OpenSSL can be challenging to install. Refer to Appendices B, Setting Up Your C Compiler on Windows, Appendices C, Setting UpYourC Compiler on Linux, and Appendices D, Setting Up Your C Compiler on macOS, for more information.
You can check whether you have the OpenSSL command-line tools installed by running the following command:
openssl versionThe following screenshot shows this on Ubuntu Linux:
You'll also need to ensure that you have the OpenSSL library installed. The following program can be used to test this. If it compiles and runs successfully, then you do have the OpenSSL library installed and working:
/*openssl_version.c*/
#include <openssl/ssl.h>
int main(int argc, char *argv[]) {
printf("OpenSSL version: %s\n", OpenSSL_version(SSLEAY_VERSION));
return 0;
}If you're using an older version of OpenSSL...