WAMP server uses php.ini located in apache bin folder. eg.
C:\wamp\bin\apache\Apache2.4.4\bin\php.ini
Whereas composer looks at PHP from CLI, and locates ini at location,
C:\wamp\bin\php\php5.4.16\php.ini
So you need to update/enable openssl in this file.
open php.ini and search 'openssl', change following
;extension=php_openssl.dll
to
extension=php_openssl.dll
and you are done