Encryption and Decryption

Microsoft Corporation

September 10, 1996

In using data encryption, a plaintext message can be encoded so it appears like random gibberish and is very difficult to transform back to the original message, without a secret key. In this document, the term message is used to refer to any piece of data. This message can consist of ASCII text, a database file, or any data you want to store or transmit securely. Plaintext is used to refer to data that has not been encrypted, while ciphertext refers to data that has.

Once a message has been encrypted, it can be stored on nonsecure media or transmitted on an nonsecure network, and still remain secret. Later, the message can be decrypted into its original form. This process is shown in the following illustration:

Figure 1. Encryption and decryption using public-key cryptography

When a message is encrypted, an encryption key is used. This is analogous to the physical key that is used to lock a padlock. To decrypt the message, the corresponding decryption key must be used. It is very important to properly restrict access to the decryption key, because anyone who possesses it will be able to decrypt all messages that were encrypted with the matching encryption key.

This may come as a surprise, but data encryption/decryption is pretty straight-forward. The really difficult part is keeping the keys safe and transmitting them securely to other users.