Since 2008, Google has been working to make sure all Google services use strong HTTPS encryption by default. That means people using products like Search, Gmail, YouTube, and Drive will automatically have an encrypted connection to Google.
In this same vein, Google is expanding on the HTTPS Everywhere mission and beginning an initial rollout of HTTPS support for Blogspot. Hence, Blogger users can now opt in to use it.
Google argues that using HTTPS will help ensure that bad actors can’t track the activities of blog authors and visitors on a site, check that visitors open the correct website and aren’t being redirected to a malicious location”
How To Enable HTTPS in Blogger
==> Sign in to Blogger.
==> Select the blog to update.
==> On the left menu, click Settings > Basic > HTTPS Settings.
==> In HTTPS Availability, select "Yes".
Once enabled, your blog will become accessible over both HTTP and HTTPS connections.
Unfortunately, blogs with custom domains are not supported in this first version. Also, if you choose to encrypt at this time, some of the current functionality of your blog may not work over HTTPS especially those that were not written for sites on secure connections. This is often caused by mixed content errors, some of which may be fixable by you.
How To Disable HTTPS in Blogger
To disable HTTPS, follow the steps above and select "No" for HTTPS Availability.
If you disable HTTPS, visitors will be redirected to the unencrypted HTTP version of your blog. All bookmarks to your blog will continue to work.
Kindly note that Google is now using HTTPS support as a ranking signal in its search results.
If your website is already serving on HTTPS, you can test its security level and configuration with the Qualys Lab tool.