Cuando hago el comando php composer.phar install me dice: <code> [Composer\Exception\NoSslException] The openssl extension is requir...

Cuando hago el comando php composer.phar install me dice:

  [Composer\Exception\NoSslException]
  The openssl extension is required for SSL/TLS protection but is not available. If you can not enable the openssl ex
  tension, you can disable this error, at your own risk, by setting the 'disable-tls' option to true.


install [--prefer-source] [--prefer-dist] [--dry-run] [--dev] [--no-dev] [--no-custom-installers] [--no-autoloader] [--no-scripts] [--no-progress] [--no-suggest] [-v|vv|vvv|--verbose] [-o|--optimize-autoloader] [-a|--classmap-authoritative] [--apcu-autoloader] [--ignore-platform-reqs] [--] [<packages>]...

¿Que puedo hacer para poder instalar composer exitosamente?