Question

One of the author’s purposes in The Code Book is to explain different types of codebreaking to his readers. Which line best demonstrates this purpose?

a theoretical breakthrough would be a fundamentally new way of finding Alice's private key
mathematicians have been studying factoring for centuries, and modern factoring techniques are not significantly better than ancient techniques
a more recent development is the so-called tempest attack, which aims to detect the electromagnetic signals emitted . . . in a computer's display unit
if scientists could build a quantum computer, it would be able to perform calculations with . . . enormous speed

Answer 1

"a more recent development is the so-called tempest attack, which aims to detect the electromagnetic signals emitted . . . in a computer's display unit"

Reason: this line explicitly names and describes a specific type of codebreaking (a side‑channel/EM attack), showing the author is explaining different methods of attacking cryptosystems.