Google hardly provides any information about the SEO ranking factors. However, last week Google officially announced that they are starting to use HTTPS as a ranking signal. As a result, using HTTPS does have an impact on the ranking positions in the search engine results pages.
According to Google this update affects fewer than 1% of global search queries for now. But Google also states that this ranking signal will be strengthened in the future and therefore encourages all website owners to switch from HTTP to HTTPS.
Google has even added best practices to the Google Help Center. These explain the necessary steps to set up HTTPS and include common pitfalls that should be avoided. To be on the safe side, these instructions should be followed.