Windows NT TCP/IP Network Administration

Encryption

Encryption is a technique for limiting access to the data carried on a network or stored in a file. Encryption encodes the data in a form that can only be read by someone who has the key to the encoding scheme. The original text, called the clear text, is encrypted using an encryption device (hardware or software) and an encryption key. This produces encoded text, which is called the cipher. To recreate the clear text, the cipher must be decrypted using the same type of encryption device and an appropriate key.

Public-key encryption is the technology that will make encryption an important security technology for data transmissions in an open global network like the Internet. Public-key systems encode the clear text with a key that is widely known and publicly available, but the cipher can only be decoded back to clear text with a secret key. This means that Dan can look up Kristin’s public-key in a trusted database and use it to encode a message to her that no one else can read. Even though everyone on the Internet has access to the public-key, only Kristin can decrypt the message using her secret key. Kristin can then look up Dan’s public-key to encrypt her reply. This encrypted communication takes place without Dan or Kristin every divulging their secret keys. However, public-key cryptography requires a trusted system for distributing public-keys to ensure that the keys have not been tampered with, and, because the encrypting key is available to everyone, it requires ...