After a long-awaited, Adsense now supports HTTPS sites, the following is the official announcement from Google Adsense blog:
Inside AdSense: Use AdSense on your HTTPS sites: Today, we're happy to announce that AdSense publishers can begin monetizing their HTTPS pages. Many websites, like e-commerce sites and social networking sites, use the HTTPS protocol to protect their users' sensitive data. If you have a HTTPS website youâll be pleased with how easy it is to monetize using AdSense.
Good news if your site is using HTTPS protocol.