Is anyone reading your email right now?

Your Gmail app just pulled three new messages at JFK, and the airport Wi-Fi you're on is shared with 0 strangers at the gate. Two technologies could be carrying those emails right now: one sends them as readable plain text through every router they pass, the other scrambles them so only Gmail's servers and your phone can decode them. Which one Gmail uses determines whether the bored engineer at gate B42 can read your inbox.