PHP lacks the OpenSSL extension.
You might go to the Wamp console in the lower right corner of the screen, load the php OpenSSL extension, or remove the comments from the Extension=php_openssl.dll line at the php.ini and restart the server, and the results are still not working.
The correct way is in the PHP installation directory, such as C:\wamp\bin\php\php5.3.3\, find a directory of the php.ini file, and then remove Extension=php_openssl.dll this line beginning of the comment, After that, you can install the composer successfully.
You can see that there are two php.ini above, yes Wamp in Apache and in CLI (command line) mode using different php.ini files, when you go to the Wamp console to enable Php_openssl This extension, is enabled for Apache, not CLI. While modifying the php.ini configuration file in the PHP installation directory, you can enable OpenSSL in CLI mode.
Installing composer in the Wamp environment of Windows