Bear in mind that as soon as Snowden started communicating with Greenwald, he knew that he was going to flee the US within a short time period, after which ther

Bear in mind that as soon as Snowden started communicating with Greenwald, he knew that he was going to flee the US within a short time period, after which there would be little damage in the NSA decrypting the historical communication logs. As such, knowing which mechanism he would choose for encryption that was required to be secure for only a few months might not be that useful.