What does “the driver’s eyes slipped over joad’s face to memorize it” mean?

Read the quote from zimmermann in the code book. a future government could inherit a technology infrastructure that's optimized for surveillance, where they can watch the movements of their political opposition, every financial transaction, every communication, every bit of e-mail, every phone call. everything could be filtered and scanned and automatically recognized by voice recognition technology and transcribed. it's time for cryptography to step out of the shadows of spies and the military, and step into the sunshine and be embraced by the rest of us. which question does this paragraph answer? why does zimmermann think encryption is important? what kind of encryption did zimmermann invent? how does zimmermann’s encryption work? who made encryption based on zimmermann’s work?