According to recent analysis by digital marketing software and services provider Searchmetrics, HTTPS does not impact rankings and there is no discernible difference between HTTP and HTTPS.
In its SEO Blog, Searchmetrics says it looked at the average rankings of both HTTP and HTTPS sites and "calculated the cumulative SEO visibilities and compared the two curves with each other over time."
The following graph includes rankings for hundreds of thousands of keywords, including a slight boost for HTTPS sites around June 2014.
However, Searchmetrics says it found "a handful of domains or individual directories, respectively, were responsible for these outliers. If these are discounted, the following picture is obtained":
HTTP stands for Hypertext Transfer Protocol. When accessing a secure site, most Web browsers will also include an encrypted protocol or Secure Sockets Layer (SSL), which is what the "S" stands for in HTTPS.
Google recently began recognizing HTTPS as a signal for rankings, but said HTTPS carries much less weight than factors like quality content.
Google also said this new signal would affect less than 1 percent of global search queries, so it's perhaps not surprising there was not a significant spike in results.