Read the excerpt from The Code Book . By this stage, sending a PGP encrypted message is becoming quite complicated. The IDEA cipher is being used to encrypt the message, RSA is being used to encrypt the IDEA key, and another stage of encryption has to be incorporated if a digital signature is required. However, Zimmermann developed his product in such a way that it would do everything automatically, so that Alice and Bob would not have to worry about the mathematics. To send a message to Bob, Alice would simply write her e-mail and select the PGP option from a menu on her computer screen. Next she would type in Bob's name, then PGP would find Bob's public key and automatically perform all the encryption. At the same time PGP would do the necessary jiggery-pokery required to digitally sign the message. Upon receiving the encrypted message, Bob would select the PGP option, and PGP would decrypt the message and verify the author. Nothing in PGP was original—Diffie and Hellman had already thought of digital signatures and other cryptographers had used a combination of symmetric and asymmetric ciphers to speed up encryption—but Zimmermann was the first to put everything together in one easy-to-use encryption product, which was efficient enough to run on a moderately sized personal computer. Which sentence is most relevant to the argument that Zimmermann’s PGP was easy to use?