This undated GCHQ presentation, which includes speaking notes, outlines different techniques for contact chaining – moving from one contact to find all those associated with it: see the Intercept article How London’s 7/7 Bombings Led to “Unprecedented” Surveillance Tactics, 1 March 2018.

This September 2008 newsletter from the National Information Assurance Research Laboratory (NIARL), an unit within the NSA’s Research Directorate gives an indication of the agency’s progress with cryptanalysis – which, with “only a handful of in-house techniques” – appears to be modest: see the Der Spiegel story Prying Eyes: Inside the NSA’s War on Internet […]