HTTPS Everywhere is a cornerstone of internet security. It makes it harder for bad actors to steal information or track the activities of blog authors and visitors. We’re rolling this out gradually and Blogspot authors interested in enabling HTTPS support can begin opting-in today. Unfortunately, blogs with custom domains are not supported in this first version. Well also be moving some of our own blogs over to HTTPS gradually, beginning with the Official Google Blog and the Google Online Security Blog. For more information, visit our Help Center.”]
Source: https://security.googleblog.com/2015/09/https-support-coming-to-blogspot.html