http://getcomposer.org/download/
You must enable the openssl extension to download files via https
解决方法：
在PHP根目录下（）找到php.ini;
Find
line ;extension=php_openssl.dll in D:\Program
Files\EasyPHP-DevServer-13.1VC9\binaries\php\php_runningversion\php.ini and
uncomment it by removing the semicolon (;) from the
beginning of the line.
原文：http://www.cnblogs.com/gmth/p/3526510.html