Question

read the excerpt from the code book. although traffic analysis, tempest attacks, viruses and trojan horses are all useful techniques for gathering information, cryptanalysts realize that their real goal is to find a way of cracking the rsa cipher, the cornerstone of modern encryption. the rsa cipher is used to protect the most important military, diplomatic, commercial and criminal communications—exactly the messages that intelligence gathering organizations want to decipher. if they are to challenge strong rsa encryption, cryptanalysts will need to make a major theoretical or technological breakthrough. what is the central idea of this paragraph? the trojan horse technique is most effective in data gathering. the rsa cipher secures much of the world’s important information. information gathering will fail without new technology development. breaking rsa code is the greatest challenge for cryptanalysts.

Explanation:

The paragraph starts by listing some information - gathering techniques (traffic analysis, tempest attacks, viruses, Trojan horses) but then emphasizes that cryptanalysts' main goal is to crack the RSA cipher. It further explains that the RSA cipher protects crucial communications and that cracking it requires a major breakthrough. The first option only focuses on the Trojan horse (a minor part of the paragraph), the second option is about what the RSA cipher does (not the central idea of the paragraph which is about cryptanalysts' goal of cracking it), the third option is not the main point as the paragraph is not about information - gathering in general but about cracking RSA. The fourth option aligns with the idea that cryptanalysts' real goal (central idea) is to break RSA and it's a great challenge.

Answer:

Breaking RSA code is the greatest challenge for cryptanalysts.