We do trust each other, this is mostly born of a conversation last week. We were talking about extending it just beyond us, but our loved ones as well, and friends. Thus “require” in this sentence does not imply we do not trust each other (we do) but that it is not necessary to work. We aren’t worried about governments and corporations with too much processing power solving np-complete problems to read these letters, though that may be other people’s threat models.