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.

The central idea of the paragraph from "The Code Book" is expressed by "Breaking the RSA code is the greatest challenge for cryptanalysts." (option D)

What is a central idea?

The central idea of a paragraph or of a whole text is the most important message behind. That is, if you were to retell that paragraph or text to someone in just a few words, you would tell them only the most important idea expressed in it. That is the central idea.

After reading the paragraph excerpted from "The Code Book," we can say that its central idea is that breaking the RSA code is the biggest challenge for cryptanalysts. According to the passage, the RSA cipher protects important information and is quite difficult to break.

With the information above in mind, we can select option D as the correct answer for this question.

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