Here`s an excellent article in EE Times on writing energy efficient ARM code https://www.eetimes.com/document.asp?doc_id=1279523 .
Our wolfSSL embedded SSL product is designed with many of these principles in mind, but of course the design goal of energy efficiency takes a back seat to overall security. In some cases, the goals of energy efficiency and overall security mesh well.
By the way, come see us at ARM TechCon. If you need a pass, let us know at firstname.lastname@example.org and we`ll send you one.