> … Mr. Snowden later sent him a homemade video with step-by-step instructions for installing [encryption software], which Mr. Greenwald watched but never compl

> … Mr. Snowden later sent him a homemade video with step-by-step instructions for installing [encryption software], which Mr. Greenwald watched but never completed… In late April or early May, he and Mr. Snowden began to talk over an encrypted chat program. What "encrypted chat program" they could possibly use?