This whitepaper by F-Secure Labs Threat Intelligence explores the tools – such as MiniDuke, CosmicDuke, OnionDuke, CozyDuke, etc- of the Dukes, a well-resourced, highly dedicated and organized cyberespionage group that they believe has been working for the Russian Federation since at least 2008 to collect intelligence in support of foreign and security policy decision-making.
However, F-Secure Labs conclude that they were unable to conclusively prove responsibility of any specific country for the Dukes. All of the available evidence however does in their opinion suggest that the group operates on behalf of the Russian Federation. Further, they are currently unaware of any evidence disproving this theory.
F-Secure Labs white paper is available here – https://www.f-secure.com/documents/996508/1030745/dukes_whitepaper.pdf