Uttam, if your issue is not solved then try the follwoing 3 step approach. It worked for me as I had exactly same issue.
step1: click on wamp tray icon.
step2: goto menu apache->apache modules
step3: click on menu item "ssl_module"
it will automatically restart wamp. if wamp not restarted automatically then restart it through wamp tray menu-> Restart All services. After restart confirm that "ssl_module" coming as ticked under menu apache->apache modules
after that just attempt the php composer.phar install from going through the response shared by you, php.ini file contains extension=php_openssl.dll and the php/ext directory also have file "php_openssl.dll"
good luck