Você não precisa do módulo openssl, ele está embutido:
$ php5.6 -r 'phpinfo();' | grep -i openssl
openssl
OpenSSL support => enabled
OpenSSL Library Version => OpenSSL 1.0.2h 3 May 2016
OpenSSL Header Version => OpenSSL 1.0.2h 3 May 2016
Openssl default config => /usr/lib/ssl/openssl.cnf
openssl.cafile => no value => no value
openssl.capath => no value => no value
Native OpenSSL support => enabled