Cryptographic techniques have been in use since the time of the Sumerians (3500 BCE). Cryptography relies on secret keys, which, as you’ll recall, are the input to the algorithm that produces the cipher text. There are two basic types of cryptography: conventional cryptography and public key cryptography. In conventional cryptography, a single key is used to perform both encryption and decryption. Because the keys are identical, they’re referred to as symmetric keys. Because only one key is used in conventional cryptography, it’s less secure. If someone other than the intended recipient discovers the key, he can decrypt the original message. Another drawback to conventional cryptography is that it’s problematic to distribute. If someone intercepts the key on its way to the intended recipient, the security of the message is compromised. PGP Desktop also allows you to encrypt individual files and folders, a portion of your hard disk designated as a virtual disk, or your entire hard disk.In public key cryptography, two distinct keys are used-a public key to perform encryption and a private key to perform decryption. Because the keys are different, they’re referred to as asymmetric keys. This allows anyone to encrypt a message but only individuals with the corresponding private key to decrypt messages. To clarify, let’s look at an example. If Paul wants to send a message to Sara, he uses Sara’s public key to encrypt the message. When Sara receives the message, she uses her private key to decrypt it. As long as each person in the message loop keeps his/her private key absolutely private, only the intended recipient can decrypt the message. Public cryptography also overcomes the distribution problem because only public keys need to be sent over the insecure network; private keys are maintained locally.Next, let’s turn our attention to a practical example of public key cryptography. In the following sections, we’ll use a sample application, PGP Desktop, to show you how to generate a public/private key pair to secure both email and instant messages. We’ll also show you how to publish your public key to the PGP Global Directory so others can send encrypted messages to you. When your machine comes back online, the PGP Setup Assistant launches automatically. This utility helps you complete an initial setup, including generating a new key pair and optionally publishing your public key to the PGP Global Directory. It’s important to note that you must complete the PGP Setup Assistant tasks prior to using the primary application itself. Because PGP is installed for all users by default, you need to enable it for each Windows account individually. This means that you need to first log in with the appropriate Windows account, and then enable PGP for the active account.
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