In the webmaster blog Google announced its preference of HTTPS over HTTP protocol. This was bound to be since the search company is quite conscious of visitor privacy and security. Simply put this protocol encrypts message to be sent and on arrival decrypts messages to be received over HTTP protocol.
HTTPS is a security protocol which carries a connection encrypted by TLS or Transfer Security Layer. The main objective is to secure visitor interest, prevent malicious packet injection Ad inserts, information espionage and privacy of course. Hence Data Exchange takes place in a secured environment for the benefit of the user.
Earlier this protocol was used for electronic payment systems over the WWW or Web. It was also preferred by corporate portals and e-mail providers in order to attain extreme secrecy.
Browser software and certification authorities should be trustworthy in this type of data exchange. Some of the certification authorities are: Symantec, Comodo, GoDaddy and GlobalSign.
The encryption protection layer should also be trustworthy and provide security. However HTTPS can be called reasonably secure and do prevent tempering and malicious attacks but they are not hundred percent foolproof.
Keeping in mind the good aspects of this protocol the search engine company will give preference to it over HTTP which is not as secured.
In this case the port used is 443 and the URL begins with https://
For More Information visit: HTTPS
Read at Google Webmaster Blog for more information on HTTPS