This past week, the NATO Cooperative Cyber Defense Center of Excellence put on its annual Cyber Conflict conference in Tallinn, Estonia. The conference boasted a number of experienced cyber-hands, including Adm. Mike Rodgers, DefCon founder Jeff Moss, and law of armed conflict expert Mike Schmitt. One of the most interesting sessions, which included a presentation by Mike, focused on aspects of the Tallinn Manual versions 1.0 and 2.0. Version 1.0, produced by an independent group of experts, came out in 2013. It proffered what the experts saw as current black letter law on jus ad bellum and jus in bello rules relevant to cyber operations. The Manual includes both crisp articulations of the rules and more extensive commentary setting out the legal basis for the rule and any differences that arose among the experts. 

Ashley S. Deeks, Tallinn 2.0 and a Chinese View on the Tallinn Process, Lawfare (May 31, 2015).