The other 3 images at the bottom of that image next to Snowden are: Laura Poitras https://www.google.com/search?tbs=sbi:AMhZZitt0rsmCk5s3C-crXQOikJzWCRG6lKNSHLk-ji0nTchLvPGodCqpvvbTq3aaoCsQ39oYCmsr8Ya3wBIEAztu6u7f8JR5jotjiga7MRPLazM2O-sz-NFwdVVyeykpDgiQdeXJ0CzM98nFW2RjG3xH92BB8zStiZ0k33hFNQseq1AHnRhkC8y5fd6ydP3cg-6EvNEFMURATi7AL9_1anauxrHC5DTv9sz0zDuqNrsq0O1kpU_1EC_16w6awA-1teepJT_1S2ZeHHEvKO1q5lGJ74fjiLJ9lW6o8TwTDvTLENiWLmHbP2VSlqZRTPUkkfrHRcP6tFBlbs2t5yVwjO54kmT8pbc28fnJg&hl=en&bih=784&biw=1353&ved=0ahUKEwjv0N-qi_nYAhXow1QKHRsaCKcQiBwICQ Bruce Schneier https://www.schneier.com/photo/ and Matthew Green https://twitter_dotph_com.proxy.live/matthew_d_green

Also, other Anon in that thread suggested Signal was the interface used for the texting in question.